sds简单的动态字符串(sds.h sds.c)

sds.h

/**
 * redis 动态字符串
 */
#ifndef __SDS_H
#define __SDS_H
#define SDS_MAX_PREALLOC (1024*1024)
extern const char *SDS_NOINIT;
#include <sys/types.h>
#include <stdarg.h>
#include <stdint.h>
/**
 *  sds 类型是 char * 的别名
 */
typedef char *sds;
/* Note: sdshdr5 is never used, we just access the flags byte directly.
 * However is here to document the layout of type 5 SDS strings. */
// 根据存储的内容选择不同数据结构，以节省内存
// 这里的 '__attribute__ ((__packed__))' 要求编译器取消内存对齐优化，按照实际的占用字节数进行对齐
// string_size < 32
struct __attribute__ ((__packed__)) sdshdr5 {
    /**
     * 前 5 位保存字符串长度，后 3 位保存类型值
     */
    unsigned char flags; /* 3 lsb of type, and 5 msb of string length */
    //实际保存字符串数据的地方以及末尾的一个 \0
    char buf[];
};
// 32 <= string_size < 256
struct __attribute__ ((__packed__)) sdshdr8 {
    /* 记录当前 buf 的长度（不包含 '\0'） */
    uint8_t len; /* used */
    /* 记录当前 buf 总共分配的内存大小（不包含 '\0'） */
    uint8_t alloc; /* excluding the header and null terminator */
    /* 记录当前 buf 的属性，用来标识到底是 sdshdr8 还是 sdshdr16 等 */
    unsigned char flags;
    // 实际保存字符串数据的地方以及末尾的一个 \0
    char buf[];
};
// 256 <= string_size < 65536(64K)
struct __attribute__ ((__packed__)) sdshdr16 {
    // 记录当前 buf 的长度（不包含 '\0'）
    uint16_t len; /* used */
    // 记录当前 buf 总共分配的内存大小（不包含 '\0'
    uint16_t alloc; /* excluding the header and null terminator */
    //记录当前 buf 的属性，用来标识到底是 sdshdr8 还是 sdshdr16 等
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    // 实际保存字符串数据的地方以及末尾的一个 \0
    char buf[];
};
// 65536(64K) <= string_size < 4GB
struct __attribute__ ((__packed__)) sdshdr32 {
    //记录当前 buf 的长度（不包含 '\0'）
    uint32_t len; /* used */
    //记录当前 buf 总共分配的内存大小（不包含 '\0'）
    uint32_t alloc; /* excluding the header and null terminator */
    //记录当前 buf 的属性等
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    // 实际保存字符串数据的地方以及末尾的一个 \0
    char buf[];
};
// 4G <= string_size
struct __attribute__ ((__packed__)) sdshdr64 {
    //记录当前 buf 的长度（不包含 '\0'）
    uint64_t len; /* used */
    //记录当前 buf 总共分配的内存大小（不包含 '\0'）
    uint64_t alloc; /* excluding the header and null terminator */
    //记录当前 buf 的属性等
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    // 实际保存字符串数据的地方以及末尾的一个 \0
    char buf[];
};
// flags 值的定义
#define SDS_TYPE_5  0
#define SDS_TYPE_8  1
#define SDS_TYPE_16 2
#define SDS_TYPE_32 3
#define SDS_TYPE_64 4
// 掩码，flags & SDS_TYPE_MASK 即可获得具体的 flags 值
#define SDS_TYPE_MASK 7
#define SDS_TYPE_BITS 3
// 这里的 s 是一个 sds
// 可以通过 sds 的头指针进行寻址，拿到整个 struct 的指针
// buf[-1]的值是flags的值  存的值再内存中是连续的 (len alloc flags buf)
#define SDS_HDR_VAR(T,s) struct sdshdr##T *sh = (void*)((s)-(sizeof(struct sdshdr##T)));
#define SDS_HDR(T,s) ((struct sdshdr##T *)((s)-(sizeof(struct sdshdr##T))))
#define SDS_TYPE_5_LEN(f) ((f)>>SDS_TYPE_BITS)
//判断字符串长度  inline内联
static inline size_t sdslen(const sds s) {
    // 通过 buf 的 -1 下标获取 flags 的值
    unsigned char flags = s[-1];
    //SDS_TYPE_MASK = 7  flags&SDS_TYPE_MASK运算获取flags具体的值
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5:
            //flags的值 flags >> 3
            return SDS_TYPE_5_LEN(flags);
        case SDS_TYPE_8:
            //SDS_HDR(8,s) ==  ((struct sdshdr8 *)((s)-(sizeof(struct sdshdrT8)))->len  sdshdr8的len方法
            return SDS_HDR(8,s)->len;
        case SDS_TYPE_16:
            return SDS_HDR(16,s)->len;
        case SDS_TYPE_32:
            return SDS_HDR(32,s)->len;
        case SDS_TYPE_64:
            return SDS_HDR(64,s)->len;
    }
    return 0;
}
//sds可用内存大小
static inline size_t sdsavail(const sds s) {
    //s[-1]的值是flags的值， 要求编译器取消内存对齐优化，按照实际的占用字节数进行对齐，buf的前面是flags
    unsigned char flags = s[-1];
    //flags&SDS_TYPE_MASK运算获取flags具体的值
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5: {
            return 0;
        }
        //sh->alloc - sh->len; 分配内存大小减去字符串长度
        case SDS_TYPE_8: {
            SDS_HDR_VAR(8,s);
            return sh->alloc - sh->len;
        }
        case SDS_TYPE_16: {
            SDS_HDR_VAR(16,s);
            return sh->alloc - sh->len;
        }
        case SDS_TYPE_32: {
            SDS_HDR_VAR(32,s);
            return sh->alloc - sh->len;
        }
        case SDS_TYPE_64: {
            SDS_HDR_VAR(64,s);
            return sh->alloc - sh->len;
        }
    }
    return 0;
}
//给sds设置新的长度
static inline void sdssetlen(sds s, size_t newlen) {
    //获取flags的值
    unsigned char flags = s[-1];
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5:
            {
                unsigned char *fp = ((unsigned char*)s)-1;
                /**
                 * 位或|  二进制中只要有一个为1 就位1   10010 | 01100 = 11110
                 * 左移 <<     newlen << 3  = newlen * 2^3 = newlen * 8
                 */
                //0 | newlen  * 8 = newlen * 8
                *fp = SDS_TYPE_5 | (newlen << SDS_TYPE_BITS);
            }
            break;
        case SDS_TYPE_8:
            SDS_HDR(8,s)->len = newlen;
            break;
        case SDS_TYPE_16:
            SDS_HDR(16,s)->len = newlen;
            break;
        case SDS_TYPE_32:
            SDS_HDR(32,s)->len = newlen;
            break;
        case SDS_TYPE_64:
            SDS_HDR(64,s)->len = newlen;
            break;
    }
}
/**
 * 增加sds字符串长度
 * @param s 字符串
 * @param inc  新的长度
 */
static inline void sdsinclen(sds s, size_t inc) {
    unsigned char flags = s[-1];
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5:
            {
                unsigned char *fp = ((unsigned char*)s)-1;
                unsigned char newlen = SDS_TYPE_5_LEN(flags)+inc;
                *fp = SDS_TYPE_5 | (newlen << SDS_TYPE_BITS);
            }
            break;
        case SDS_TYPE_8:
            SDS_HDR(8,s)->len += inc;
            break;
        case SDS_TYPE_16:
            SDS_HDR(16,s)->len += inc;
            break;
        case SDS_TYPE_32:
            SDS_HDR(32,s)->len += inc;
            break;
        case SDS_TYPE_64:
            SDS_HDR(64,s)->len += inc;
            break;
    }
}
/**
 * sds 分配的大小  = sds可用大小 + sds长度
 * @param s  字符串
 * @return
 */
/* sdsalloc() = sdsavail() + sdslen() */
static inline size_t sdsalloc(const sds s) {
    unsigned char flags = s[-1];
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5:
            //flags >> 3  = flags / 8
            return SDS_TYPE_5_LEN(flags);
        case SDS_TYPE_8:
            return SDS_HDR(8,s)->alloc;
        case SDS_TYPE_16:
            return SDS_HDR(16,s)->alloc;
        case SDS_TYPE_32:
            return SDS_HDR(32,s)->alloc;
        case SDS_TYPE_64:
            return SDS_HDR(64,s)->alloc;
    }
    return 0;
}
/**
 * 设置字符串可用内存为新分配的内存
 * @param s  字符串
 * @param newlen  新的长度
 */
static inline void sdssetalloc(sds s, size_t newlen) {
    unsigned char flags = s[-1];
    //选择那种字符串类型
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5:
            /* Nothing to do, this type has no total allocation info. */
            break;
        case SDS_TYPE_8:
            //设置字符串buf内存 sds->alloc = newlen
            SDS_HDR(8,s)->alloc = newlen;
            break;
        case SDS_TYPE_16:
            SDS_HDR(16,s)->alloc = newlen;
            break;
        case SDS_TYPE_32:
            SDS_HDR(32,s)->alloc = newlen;
            break;
        case SDS_TYPE_64:
            SDS_HDR(64,s)->alloc = newlen;
            break;
    }
}
//创建一个initlen长度的sds字符串，如果创建不成功会返回异常
sds sdsnewlen(const void *init, size_t initlen);
//尝试创建initlen长度的sds字符串，创建不成功返回NULL
sds sdstrynewlen(const void *init, size_t initlen);
//给字符串init创建一个sdh
sds sdsnew(const char *init);
//创建一个空字符串
sds sdsempty(void);
//复制字符串
sds sdsdup(const sds s);
//释放字符串
void sdsfree(sds s);
//扩展sds字符串长度
sds sdsgrowzero(sds s, size_t len);
//sds连接固定长度len的char字符串
sds sdscatlen(sds s, const void *t, size_t len);
//sds连接char字符串，模仿strcat
sds sdscat(sds s, const char *t);
//sds连接sds字符串，模仿strcat
sds sdscatsds(sds s, const sds t);
//sds拷贝固定长度len的char字符串
sds sdscpylen(sds s, const char *t, size_t len);
//sds拷贝char字符串
sds sdscpy(sds s, const char *t);
//sds连接格式化字符串，采用C实现格式功能
sds sdscatvprintf(sds s, const char *fmt, va_list ap);
#ifdef __GNUC__
sds sdscatprintf(sds s, const char *fmt, ...)
    __attribute__((format(printf, 2, 3)));
#else
sds sdscatprintf(sds s, const char *fmt, ...);
#endif
//sds连接格式化字符串，自定义格式化功能
sds sdscatfmt(sds s, char const *fmt, ...);
// 前后去掉字符 cset
sds sdstrim(sds s, const char *cset);
void sdssubstr(sds s, size_t start, size_t len);
//截断字符串
void sdsrange(sds s, ssize_t start, ssize_t end);
//更新字符串长度
void sdsupdatelen(sds s);
//清空sds字符串
void sdsclear(sds s);
//比较两个sds字符串
int sdscmp(const sds s1, const sds s2);
//sds分割函数  对于strsplit
sds *sdssplitlen(const char *s, ssize_t len, const char *sep, int seplen, int *count);
//释放分割出来的sds
void sdsfreesplitres(sds *tokens, int count);
//sds转小写
void sdstolower(sds s);
//sds转大写
void sdstoupper(sds s);
//longlong类型转化为sds字符串
sds sdsfromlonglong(long long value);
//sds添加转义字符字符串
sds sdscatrepr(sds s, const char *p, size_t len);
//sds根据转义字符分割，必须用sdsfreesplitres().
sds *sdssplitargs(const char *line, int *argc);
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen);
//字符串连接后，转化为sds
sds sdsjoin(char **argv, int argc, char *sep);
//sds 连接sds
sds sdsjoinsds(sds *argv, int argc, const char *sep, size_t seplen);
/* Callback for sdstemplate. The function gets called by sdstemplate
 * every time a variable needs to be expanded. The variable name is
 * provided as variable, and the callback is expected to return a
 * substitution value. Returning a NULL indicates an error.
 */
typedef sds (*sdstemplate_callback_t)(const sds variable, void *arg);
//sds回调模板函数
sds sdstemplate(const char *template, sdstemplate_callback_t cb_func, void *cb_arg);
// sds扩展函数 sds的扩容
/* Low level functions exposed to the user API */
sds sdsMakeRoomFor(sds s, size_t addlen);
//配合sdsMakeRoomFor使用，重置sds长度
void sdsIncrLen(sds s, ssize_t incr);
//sds释放空闲空间
sds sdsRemoveFreeSpace(sds s);
//计算sds开辟空间的大小
size_t sdsAllocSize(sds s);
//返回buf缓冲指针
void *sdsAllocPtr(sds s);
/* Export the allocator used by SDS to the program using SDS.
 * Sometimes the program SDS is linked to, may use a different set of
 * allocators, but may want to allocate or free things that SDS will
 * respectively free or allocate. */
//开辟size大小的空间
void *sds_malloc(size_t size);
//如果size> ptr.length 重新开辟size大小的空间
void *sds_realloc(void *ptr, size_t size);
//释放指针空间
void sds_free(void *ptr);
#ifdef REDIS_TEST
int sdsTest(int argc, char *argv[], int accurate);
#endif
#endif

sds.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include <limits.h>
#include "sds.h"
#include "sdsalloc.h"
/**
 * 常量
 */
const char *SDS_NOINIT = "SDS_NOINIT";
/**
 * 获取sds类型结构占用的内存大小
 * @param type  sds的类型
 * @return  内存大小
 */
static inline int sdsHdrSize(char type) {
    switch(type&SDS_TYPE_MASK) {
        case SDS_TYPE_5:
            return sizeof(struct sdshdr5);
        case SDS_TYPE_8:
            return sizeof(struct sdshdr8);
        case SDS_TYPE_16:
            return sizeof(struct sdshdr16);
        case SDS_TYPE_32:
            return sizeof(struct sdshdr32);
        case SDS_TYPE_64:
            return sizeof(struct sdshdr64);
    }
    return 0;
}
/**
 * 通过sds字符串长度获取所需要的sds类型
 * @param string_size  字符串长度
 * @return 字符串类型
 */
static inline char sdsReqType(size_t string_size) {
    //string_size < 2^5 = string_size < 32
    if (string_size < 1<<5)
        return SDS_TYPE_5;
    // 32 <= string_size < 256
    if (string_size < 1<<8)
        return SDS_TYPE_8;
    // 256 <= string_size < 65536(64K)
    if (string_size < 1<<16)
        return SDS_TYPE_16;
    // LONG_MAX == LLONG_MAX = 8 代表64位系统
#if (LONG_MAX == LLONG_MAX)
// 65536(64K) <= string_size < 4GB
if (string_size < 1ll<<32)
    return SDS_TYPE_32;
// 4G <= string_size
return SDS_TYPE_64;
#else
//32位系统
return SDS_TYPE_32;
#endif
}
/**
 * 获取sds字符串在该类型中的允许的最大长度
 * @param type 类型
 * @return 长度
 */
static inline size_t sdsTypeMaxSize(char type) {
    if (type == SDS_TYPE_5)
        return (1<<5) - 1;
    if (type == SDS_TYPE_8)
        return (1<<8) - 1;
    if (type == SDS_TYPE_16)
        return (1<<16) - 1;
#if (LONG_MAX == LLONG_MAX)
    //预编译命令 代表64位系统
    if (type == SDS_TYPE_32)
        return (1ll<<32) - 1;
#endif
    //-1 相当于最大的 SDS_TYPE_64 或者 SDS_TYPE_32
    return -1; /* this is equivalent to the max SDS_TYPE_64 or SDS_TYPE_32 */
}
/* Create a new sds string with the content specified by the 'init' pointer
 * and 'initlen'.
 * If NULL is used for 'init' the string is initialized with zero bytes.
 * If SDS_NOINIT is used, the buffer is left uninitialized;
 *
 * The string is always null-termined (all the sds strings are, always) so
 * even if you create an sds string with:
 *
 * mystring = sdsnewlen("abc",3);
 *
 * You can print the string with printf() as there is an implicit \0 at the
 * end of the string. However the string is binary safe and can contain
 * \0 characters in the middle, as the length is stored in the sds header. */
/**
 * 用于创建sds字符串
 * const void *init 代表任何类型的值
 * @param init  init指针   init 代表任何类型的值，值为常量，无法修改其值，但是可以其使指针指向其他对象
 * @param initlen  字符串长度
 * @param trymalloc 分配的buf大小
 * @return sds字符串
 */
sds _sdsnewlen(const void *init, size_t initlen, int trymalloc) {
    void *sh;
    sds s;
    //通过sds字符串长度获取sds类型
    char type = sdsReqType(initlen);
    /* Empty strings are usually created in order to append. Use type 8
     * since type 5 is not good at this. */
    // 如果类型SDS_TYPE_5 并且长度位0 则类型设置为 SDS_TYPE_8 ，空的字符串通常使用类型SDS_TYPE_8，以便于追加字符，
    if (type == SDS_TYPE_5 && initlen == 0) type = SDS_TYPE_8;
    //sds 的类型占用的内存的大小
    int hdrlen = sdsHdrSize(type);
    //定义flags标识 标识sds的buf属性
    unsigned char *fp; /* flags pointer. */
    size_t usable;
    //断言 字符串长度 + 类型占用的长度 + 1 >  字符串长度
    assert(initlen + hdrlen + 1 > initlen); /* Catch size_t overflow */
    // 分配内存的大小 sh如果为NULL则分配失败  否则usable为分配的可用内存大小
    sh = trymalloc?
        s_trymalloc_usable(hdrlen+initlen+1, &usable) :
        s_malloc_usable(hdrlen+initlen+1, &usable);
    //如果分配内存失败则返回 NULL
    if (sh == NULL) return NULL;
    // 如果init==SDS_NOINIT(这里判断地址是否相同)，设置init为NULL
    if (init==SDS_NOINIT)
        init = NULL;
    else if (!init)
        // 清空内存内容
        memset(sh, 0, hdrlen+initlen+1);
    // c字符串
    s = (char*)sh+hdrlen;
    // 标志位（sdshdr_xx中flags）
    fp = ((unsigned char*)s)-1;
    //字符串可用内存大小 = 分配的内存大小-sds结构大小-1
    usable = usable-hdrlen-1;
    //判断可用内存大小 是否大于该类型最大可用大小
    if (usable > sdsTypeMaxSize(type))
        //是的话分配该类型最大可用内存大小
        usable = sdsTypeMaxSize(type);
    // 根据得到的sds类型设置头部信息
    switch(type) {
        case SDS_TYPE_5: {
            *fp = type | (initlen << SDS_TYPE_BITS);
            break;
        }
        case SDS_TYPE_8: {
            SDS_HDR_VAR(8,s);
            sh->len = initlen;
            sh->alloc = usable;
            *fp = type;
            break;
        }
        case SDS_TYPE_16: {
            SDS_HDR_VAR(16,s);
            sh->len = initlen;
            sh->alloc = usable;
            *fp = type;
            break;
        }
        case SDS_TYPE_32: {
            SDS_HDR_VAR(32,s);
            sh->len = initlen;
            sh->alloc = usable;
            *fp = type;
            break;
        }
        case SDS_TYPE_64: {
            SDS_HDR_VAR(64,s);
            sh->len = initlen;
            sh->alloc = usable;
            *fp = type;
            break;
        }
    }
    // 拷贝字符串到sds字符串中
    if (initlen && init)
        memcpy(s, init, initlen);
    // 设置标准结束符
    s[initlen] = '\0';
    return s;
}
/**
 * 创建sds字符串 使用s_malloc_usable创建内存空间
 * @param init 任意类型的值  常量 值不可更改  但指针可以更改指向的对象
 * @param initlen
 * @return 字符串
 */
sds sdsnewlen(const void *init, size_t initlen) {
    return _sdsnewlen(init, initlen, 0);
}
/**
 * 尝试创建sds，使用s_trymalloc_usable创建内存空间
 * @param init 任意类型的值
 * @param initlen
 * @return
 */
sds sdstrynewlen(const void *init, size_t initlen) {
    return _sdsnewlen(init, initlen, 1);
}
/**
 * 创建0长度的字符串
 * @return sds字符串
 */
/* Create an empty (zero length) sds string. Even in this case the string
 * always has an implicit null term. */
sds sdsempty(void) {
    return sdsnewlen("",0);
}
/**
 * 从一个以null结尾的 C字符串 创建一个新的sds字符串
 * @param init
 * @return
 */
/* Create a new sds string starting from a null terminated C string. */
sds sdsnew(const char *init) {
    // 判断传入的字符串是否为NULL 如果为NULL为创建一个空的sds字符串，否则创建strlen(init)长度的sds字符串
    size_t initlen = (init == NULL) ? 0 : strlen(init);
    return sdsnewlen(init, initlen);
}
/**
 *  复制一个sds
 * @param s
 * @return
 */
/* Duplicate an sds string. */
sds sdsdup(const sds s) {
    return sdsnewlen(s, sdslen(s));
}
/**
 * 释放sds字符串
 * @param s sds字符串
 */
/* Free an sds string. No operation is performed if 's' is NULL. */
void sdsfree(sds s) {
    //如果sds字符串为NULL为不作操作
    if (s == NULL) return;
    //释放内存空间
    s_free((char*)s-sdsHdrSize(s[-1]));
}
/* Set the sds string length to the length as obtained with strlen(), so
 * considering as content only up to the first null term character.
 *
 * This function is useful when the sds string is hacked manually in some
 * way, like in the following example:
 *
 * s = sdsnew("foobar");
 * s[2] = '\0';
 * sdsupdatelen(s);
 * printf("%d\n", sdslen(s));
 *
 * The output will be "2", but if we comment out the call to sdsupdatelen()
 * the output will be "6" as the string was modified but the logical length
 * remains 6 bytes. */
/**
 * 将sds的已经使用的长度修改成第一个'\0'结尾的字符串的长度，相当于从第一个\0截断
 *
 * 当修改给sds字符串中某一个字符为'\0' ，
 * 此时需要执行该方法去更新sds字符串长度，因为sds长度记录在sds头len中，如果不去更新，则sds长度不变，
 * 例子：
 *      s = sdsnew("foobar");
 *      s[2] = '\0';
 *      dsupdatelen(s);
 *      rintf("%d\n", sdslen(s));
 *     此时输出长度为2
 *    如果没有dsupdatelen(s); 则sds长度还是原来的6
 * @param s
 */
void sdsupdatelen(sds s) {
    //获取sds长度即 到第一个'\0'的长度
    size_t reallen = strlen(s);
    // 给sds设置新的长度
    sdssetlen(s, reallen);
}
/* Modify an sds string in-place to make it empty (zero length).
 * However all the existing buffer is not discarded but set as free space
 * so that next append operations will not require allocations up to the
 * number of bytes previously available. */
/**
 * 将sds的内存清零但不释放
 * 设置sds长度为0，并将第一个字符位置设置为结束符 '\0'
 * @param s
 */
void sdsclear(sds s) {
    sdssetlen(s, 0);
    s[0] = '\0';
}
/* Enlarge the free space at the end of the sds string so that the caller
 * is sure that after calling this function can overwrite up to addlen
 * bytes after the end of the string, plus one more byte for nul term.
 *
 * Note: this does not change the *length* of the sds string as returned
 * by sdslen(), but only the free buffer space we have. */
/**
 * 给一个sds扩充空间以供以后使用
 * 该方法用于添加sds字符串sds的alloc的小 即可用空间大小，不会改变字符串长度
 * @param s  sds字符串
 * @param addlen  需要新增的大小
 * @return sds字符串
 */
sds sdsMakeRoomFor(sds s, size_t addlen) {
    void *sh, *newsh;
    //获取sds当前可用空间
    size_t avail = sdsavail(s);
    size_t len, newlen, reqlen;
    //获取sds的类型 s[-1]= flags  oldtype = flags & SDS_TYPE_MASK;
    char type, oldtype = s[-1] & SDS_TYPE_MASK;
    int hdrlen;
    size_t usable;
    //如果可用空间大于扩容大小 则无须扩容直接返回
    /* Return ASAP if there is enough space left. */
    if (avail >= addlen) return s;
    //判断字符串长度
    len = sdslen(s);
    //获取sds类型结构占用的内存大小
    sh = (char*)s-sdsHdrSize(oldtype);
    //新的内存大小等于  sds字符串长度+新增长度
    reqlen = newlen = (len+addlen);
    //断言 新增后的长度要大于 sds字符串长度
    assert(newlen > len);   /* Catch size_t overflow */
    //如果新的长度小于 1M,则扩容为其2倍
    if (newlen < SDS_MAX_PREALLOC)
        newlen *= 2;
    //否则+1M
    else
        newlen += SDS_MAX_PREALLOC;
    //修改要扩容sds字符串的类型
    type = sdsReqType(newlen);
    /* Don't use type 5: the user is appending to the string and type 5 is
     * not able to remember empty space, so sdsMakeRoomFor() must be called
     * at every appending operation. */
    //如果类型是SDS_TYPE_5 的话将类型设置为 SDS_TYPE_8
    if (type == SDS_TYPE_5) type = SDS_TYPE_8;
    //获取新的类型的结构占用的空间大小
    hdrlen = sdsHdrSize(type);
    //断言 新的类型结构占用的空间 + 扩容后的长度+1 要大于 扩容前sds字符串长度+addlen新增长度
    assert(hdrlen + newlen + 1 > reqlen);  /* Catch size_t overflow */
    if (oldtype==type) {
        //如果旧的类型和新的类型一致,则重新分配内存
        newsh = s_realloc_usable(sh, hdrlen+newlen+1, &usable);
        if (newsh == NULL) return NULL;
        s = (char*)newsh+hdrlen;
    } else {
        /* Since the header size changes, need to move the string forward,
         * and can't use realloc */
        //如果新类型和旧内存不一致则重新创建一个新的内存空间
        //分配内存 如果为NULL则内存分配失败 否则usable为可用内存大小
        newsh = s_malloc_usable(hdrlen+newlen+1, &usable);
        if (newsh == NULL) return NULL;
        //复制字符串
        memcpy((char*)newsh+hdrlen, s, len+1);
        //释放之前的sds字符串
        s_free(sh);
        s = (char*)newsh+hdrlen;
        //设置新标识
        s[-1] = type;
        //给sds设置新的长度
        sdssetlen(s, len);
    }
    //可用内存 = 分配的可用内存-sds类型结构内存-1
    usable = usable-hdrlen-1;
    //如果可用内存 > 类型最大的内存则重新设置sds类型
    if (usable > sdsTypeMaxSize(type))
        usable = sdsTypeMaxSize(type);
    //设置字符串可用内存为新分配的内存
    sdssetalloc(s, usable);
    return s;
}
/* Reallocate the sds string so that it has no free space at the end. The
 * contained string remains not altered, but next concatenation operations
 * will require a reallocation.
 *
 * After the call, the passed sds string is no longer valid and all the
 * references must be substituted with the new pointer returned by the call. */
/**
 * 根据实际使用长度减少sds的分配内存 设置sds可用空间为0
 * 重新分配sds字符串内存空间，传入的s字符串将不可以，指针将指向新创建的sds字符串
 * @param s sds字符串
 * @return
 */
sds sdsRemoveFreeSpace(sds s) {
    void *sh, *newsh;
    //s[-1] = flags  sds类型
    char type, oldtype = s[-1] & SDS_TYPE_MASK;
    int hdrlen, oldhdrlen = sdsHdrSize(oldtype);
    //获取sds字符串长度
    size_t len = sdslen(s);
    //获取s的可用内存
    size_t avail = sdsavail(s);
    //sda的buf长度 = sds长度 - sds类型结构占用的内存空间大小
    sh = (char*)s-oldhdrlen;
    //如果可用空间已经为0，那么无须调整
    /* Return ASAP if there is no space left. */
    if (avail == 0) return s;
    /* Check what would be the minimum SDS header that is just good enough to
     * fit this string. */
    //获取该长度所需要的的sds类型
    type = sdsReqType(len);
    //获取sds类型结构占用的内存大小
    hdrlen = sdsHdrSize(type);
    /* If the type is the same, or at least a large enough type is still
     * required, we just realloc(), letting the allocator to do the copy
     * only if really needed. Otherwise if the change is huge, we manually
     * reallocate the string to use the different header type. */
    if (oldtype==type || type > SDS_TYPE_8) {
        //如果旧sds类型和 sds字符串最少需要的sds类型一致,重新分配内存并将之前sds内存释放
        newsh = s_realloc(sh, oldhdrlen+len+1);
        //如果分配失败则返回NULL
        if (newsh == NULL) return NULL;
        //c 字符串
        s = (char*)newsh+oldhdrlen;
    } else {
        //sds字符串最少需要空间的sds类型 和 原sds类型不一致 分配内存
        newsh = s_malloc(hdrlen+len+1);
        //如果为NULL则分配失败
        if (newsh == NULL) return NULL;
        //复制
        memcpy((char*)newsh+hdrlen, s, len+1);
        //释放原sds串内存
        s_free(sh);
        // c串
        s = (char*)newsh+hdrlen;
        //设置新的类型
        s[-1] = type;
        //设置新的sds长度
        sdssetlen(s, len);
    }
    //设置sds可用内存为0的内存
    sdssetalloc(s, len);
    return s;
}
/* Return the total size of the allocation of the specified sds string,
 * including:
 * 1) The sds header before the pointer.
 * 2) The string.
 * 3) The free buffer at the end if any.
 * 4) The implicit null term.
 */
// 返回一个sds的总长度，包括头，二进制字符串分配的内存长度和'\0'
size_t sdsAllocSize(sds s) {
    //sds分配的内存大小
    size_t alloc = sdsalloc(s);
    // sds类型结构占用的内存大小 + 可用内存空间 + 1
    return sdsHdrSize(s[-1])+alloc+1;
}
/* Return the pointer of the actual SDS allocation (normally SDS strings
 * are referenced by the start of the string buffer). */
/**
 * 返回一个sds的控制结构的起始地址
 * @param  s sds字符串
 * @return 返回buf缓冲指针
 */
void *sdsAllocPtr(sds s) {
    return (void*) (s-sdsHdrSize(s[-1]));
}
/* Increment the sds length and decrements the left free space at the
 * end of the string according to 'incr'. Also set the null term
 * in the new end of the string.
 *
 * This function is used in order to fix the string length after the
 * user calls sdsMakeRoomFor(), writes something after the end of
 * the current string, and finally needs to set the new length.
 *
 * Note: it is possible to use a negative increment in order to
 * right-trim the string.
 *
 * Usage example:
 *
 * Using sdsIncrLen() and sdsMakeRoomFor() it is possible to mount the
 * following schema, to cat bytes coming from the kernel to the end of an
 * sds string without copying into an intermediate buffer:
 *
 * oldlen = sdslen(s);
 * s = sdsMakeRoomFor(s, BUFFER_SIZE);
 * nread = read(fd, s+oldlen, BUFFER_SIZE);
 * ... check for nread <= 0 and handle it ...
 * sdsIncrLen(s, nread);
 */
/**
 * 增加一个sds的已经使用的长度，要求加完之后不能超过分配的内存长度
 * @param s
 * @param incr
 */
void sdsIncrLen(sds s, ssize_t incr) {
    unsigned char flags = s[-1];
    size_t len;
    //判断类型
    switch(flags&SDS_TYPE_MASK) {
        case SDS_TYPE_5: {
            //标志位flags
            unsigned char *fp = ((unsigned char*)s)-1;
            unsigned char oldlen = SDS_TYPE_5_LEN(flags);
            assert((incr > 0 && oldlen+incr < 32) || (incr < 0 && oldlen >= (unsigned int)(-incr)));
            *fp = SDS_TYPE_5 | ((oldlen+incr) << SDS_TYPE_BITS);
            len = oldlen+incr;
            break;
        }
        case SDS_TYPE_8: {
            SDS_HDR_VAR(8,s);
            assert((incr >= 0 && sh->alloc-sh->len >= incr) || (incr < 0 && sh->len >= (unsigned int)(-incr)));
            len = (sh->len += incr);
            break;
        }
        case SDS_TYPE_16: {
            SDS_HDR_VAR(16,s);
            assert((incr >= 0 && sh->alloc-sh->len >= incr) || (incr < 0 && sh->len >= (unsigned int)(-incr)));
            len = (sh->len += incr);
            break;
        }
        case SDS_TYPE_32: {
            SDS_HDR_VAR(32,s);
            assert((incr >= 0 && sh->alloc-sh->len >= (unsigned int)incr) || (incr < 0 && sh->len >= (unsigned int)(-incr)));
            len = (sh->len += incr);
            break;
        }
        case SDS_TYPE_64: {
            SDS_HDR_VAR(64,s);
            assert((incr >= 0 && sh->alloc-sh->len >= (uint64_t)incr) || (incr < 0 && sh->len >= (uint64_t)(-incr)));
            len = (sh->len += incr);
            break;
        }
        default: len = 0; /* Just to avoid compilation warnings. */
    }
    s[len] = '\0';
}
/* Grow the sds to have the specified length. Bytes that were not part of
 * the original length of the sds will be set to zero.
 *
 * if the specified length is smaller than the current length, no operation
 * is performed. */
/**
 * 给一个sds的已经使用长度增加到指定长度，并将增加部分内存清零
 * @param s
 * @param len
 * @return
 */
sds sdsgrowzero(sds s, size_t len) {
    //获取sds字符串长度
    size_t curlen = sdslen(s);
    //指定的长度如果下雨当前sds字符串长度 则不做处理
    if (len <= curlen) return s;
    //sds扩容
    s = sdsMakeRoomFor(s,len-curlen);
    //如果为NULL 则内存分配失败
    if (s == NULL) return NULL;
    // s+curlen ~ len-curlen+1 区间为0
    /* Make sure added region doesn't contain garbage */
    memset(s+curlen,0,(len-curlen+1)); /* also set trailing \0 byte */
    //设置sds长度
    sdssetlen(s, len);
    return s;
}
/* Append the specified binary-safe string pointed by 't' of 'len' bytes to the
 * end of the specified sds string 's'.
 *
 * After the call, the passed sds string is no longer valid and all the
 * references must be substituted with the new pointer returned by the call. */
/**
 * 在一个sds后面连接给定长度的二进制字符串
 * @param s sds字符串
 * @param t 任意类型的值
 * @param len 长度
 * @return sds字符串
 */
sds sdscatlen(sds s, const void *t, size_t len) {
    //获取sds字符串长度
    size_t curlen = sdslen(s);
    //sds扩容
    s = sdsMakeRoomFor(s,len);
    if (s == NULL) return NULL;
    //复制字符串
    memcpy(s+curlen, t, len);
    //重新设置字符串
    sdssetlen(s, curlen+len);
    //sds末尾置'\0'
    s[curlen+len] = '\0';
    return s;
}
/* Append the specified null terminated C string to the sds string 's'.
 *
 * After the call, the passed sds string is no longer valid and all the
 * references must be substituted with the new pointer returned by the call. */
/**
 * 在一个sds后面连接一个C字符串
 * @param s
 * @param t
 * @return
 */
sds sdscat(sds s, const char *t) {
    return sdscatlen(s, t, strlen(t));
}
/* Append the specified sds 't' to the existing sds 's'.
 *
 * After the call, the modified sds string is no longer valid and all the
 * references must be substituted with the new pointer returned by the call. */
/**
 * 将一个sds的已经使用的内存连接到另一个sds中
 * @param s
 * @param t
 * @return
 */
sds sdscatsds(sds s, const sds t) {
    return sdscatlen(s, t, sdslen(t));
}
/* Destructively modify the sds string 's' to hold the specified binary
 * safe string pointed by 't' of length 'len' bytes. */
/**
 * 将一个给定长度的二进制字符串复制到sds，并更新已经使用的长度
 * @param s
 * @param t
 * @param len
 * @return
 */
sds sdscpylen(sds s, const char *t, size_t len) {
    //如果长度len大于sds分配的内存大小
    if (sdsalloc(s) < len) {
        //sds扩容
        s = sdsMakeRoomFor(s,len-sdslen(s));
        if (s == NULL) return NULL;
    }
    //复制字符串
    memcpy(s, t, len);
    s[len] = '\0';
    //设置长度
    sdssetlen(s, len);
    return s;
}
/* Like sdscpylen() but 't' must be a null-termined string so that the length
 * of the string is obtained with strlen(). */
/**
 * 将一个C字符串复制到sds
 * @param s
 * @param t
 * @return
 */
sds sdscpy(sds s, const char *t) {
    return sdscpylen(s, t, strlen(t));
}
/* Helper for sdscatlonglong() doing the actual number -> string
 * conversion. 's' must point to a string with room for at least
 * SDS_LLSTR_SIZE bytes.
 *
 * The function returns the length of the null-terminated string
 * representation stored at 's'. */
#define SDS_LLSTR_SIZE 21
/**
 * 将一个long long转换成C字符串格式
 * @param s
 * @param value
 * @return
 */
int sdsll2str(char *s, long long value) {
    char *p, aux;
    unsigned long long v;
    size_t l;
    /* Generate the string representation, this method produces
     * a reversed string. */
    v = (value < 0) ? -value : value;
    p = s;
    do {
        *p++ = '0'+(v%10);
        v /= 10;
    } while(v);
    if (value < 0) *p++ = '-';
    /* Compute length and add null term. */
    l = p-s;
    *p = '\0';
    /* Reverse the string. */
    p--;
    while(s < p) {
        aux = *s;
        *s = *p;
        *p = aux;
        s++;
        p--;
    }
    return l;
}
/**
 * 将一个unsigned long long 转换成C字符串格式
 * @param s
 * @param v
 * @return
 */
/* Identical sdsll2str(), but for unsigned long long type. */
int sdsull2str(char *s, unsigned long long v) {
    char *p, aux;
    size_t l;
    /* Generate the string representation, this method produces
     * a reversed string. */
    p = s;
    do {
        *p++ = '0'+(v%10);
        v /= 10;
    } while(v);
    /* Compute length and add null term. */
    l = p-s;
    *p = '\0';
    /* Reverse the string. */
    p--;
    while(s < p) {
        aux = *s;
        *s = *p;
        *p = aux;
        s++;
        p--;
    }
    return l;
}
/* Create an sds string from a long long value. It is much faster than:
 *
 * sdscatprintf(sdsempty(),"%lld\n", value);
 */
/**
 * 使用long long制造一个sds
 * @param value
 * @return
 */
sds sdsfromlonglong(long long value) {
    char buf[SDS_LLSTR_SIZE];
    //转换成C串
    int len = sdsll2str(buf,value);
    //创建sds字符串 使用s_malloc_usable创建内存空
    return sdsnewlen(buf,len);
}
/**
 * 将可变长格式化字符串连接到sds后面
 * @param s
 * @param fmt
 * @param ap
 * @return
 */
/* Like sdscatprintf() but gets va_list instead of being variadic. */
sds sdscatvprintf(sds s, const char *fmt, va_list ap) {
    va_list cpy;
    char staticbuf[1024], *buf = staticbuf, *t;
    //获取fmt字符串长度 * 2
    size_t buflen = strlen(fmt)*2;
    int bufstrlen;
    /* We try to start using a static buffer for speed.
     * If not possible we revert to heap allocation. */
    if (buflen > sizeof(staticbuf)) {
        // 如果格式化字符串长度*2 大于 缓冲区长度，则分配内存
        buf = s_malloc(buflen);
        if (buf == NULL) return NULL;
    } else {
        //如果格式化字符串长度*2 小于等于缓冲区大小 则设置为缓冲区大小
        buflen = sizeof(staticbuf);
    }
    /* Alloc enough space for buffer and \0 after failing to
     * fit the string in the current buffer size. */
    while(1) {
        //将ap复制到cpy
        va_copy(cpy,ap);
        //将可变参数格式化输出到一个字符数组。
        bufstrlen = vsnprintf(buf, buflen, fmt, cpy);
        //将cpy置为NULL
        va_end(cpy);
        if (bufstrlen < 0) {
            //如果bufstrlen小于0 且 buf 不等于  staticbuf释放buf 并返回NULL
            if (buf != staticbuf) s_free(buf);
            return NULL;
        }
        if (((size_t)bufstrlen) >= buflen) {
            if (buf != staticbuf) s_free(buf);
            buflen = ((size_t)bufstrlen) + 1;
            buf = s_malloc(buflen);
            if (buf == NULL) return NULL;
            continue;
        }
        break;
    }
    /* Finally concat the obtained string to the SDS string and return it. */
    //将字符串拼接到sds后面
    t = sdscatlen(s, buf, bufstrlen);
    if (buf != staticbuf) s_free(buf); //释放buf缓冲区内存
    return t;
}
/* Append to the sds string 's' a string obtained using printf-alike format
 * specifier.
 *
 * After the call, the modified sds string is no longer valid and all the
 * references must be substituted with the new pointer returned by the call.
 *
 * Example:
 *
 * s = sdsnew("Sum is: ");
 * s = sdscatprintf(s,"%d+%d = %d",a,b,a+b).
 *
 * Often you need to create a string from scratch with the printf-alike
 * format. When this is the need, just use sdsempty() as the target string:
 *
 * s = sdscatprintf(sdsempty(), "... your format ...", args);
 */
/**
 * 是sdscatvprintf的包装， 将可变长格式化字符串连接到sds后面
 * @param s
 * @param fmt
 * @param ...
 * @return
 */
sds sdscatprintf(sds s, const char *fmt, ...) {
    va_list ap;
    char *t;
    va_start(ap, fmt);
    t = sdscatvprintf(s,fmt,ap);
    va_end(ap);
    return t;
}
/* This function is similar to sdscatprintf, but much faster as it does
 * not rely on sprintf() family functions implemented by the libc that
 * are often very slow. Moreover directly handling the sds string as
 * new data is concatenated provides a performance improvement.
 *
 * However this function only handles an incompatible subset of printf-alike
 * format specifiers:
 *
 * %s - C String
 * %S - SDS string
 * %i - signed int
 * %I - 64 bit signed integer (long long, int64_t)
 * %u - unsigned int
 * %U - 64 bit unsigned integer (unsigned long long, uint64_t)
 * %% - Verbatim "%" character.
 */
/**
 * 和sdscatvprintf功能一样，区别是不使用sprintf族函数，性能高
 * @param s
 * @param fmt
 * @param ...
 * @return
 */
sds sdscatfmt(sds s, char const *fmt, ...) {
    //initlen= s长度
    size_t initlen = sdslen(s);
    const char *f = fmt;
    long i;
    va_list ap;
    /* To avoid continuous reallocations, let's start with a buffer that
     * can hold at least two times the format string itself. It's not the
     * best heuristic but seems to work in practice. */
    //sds扩容
    s = sdsMakeRoomFor(s, strlen(fmt)*2);
    //宏  ap储存fmt参数
    va_start(ap,fmt);
    f = fmt;    /* Next format specifier byte to process. */
    i = initlen; /* Position of the next byte to write to dest str. */
    while(*f) {
        char next, *str;
        size_t l;
        long long num;
        unsigned long long unum;
        /* Make sure there is always space for at least 1 char. */
        if (sdsavail(s)==0) {
            //如果可用空间为0，则扩容，内存大小+1
            s = sdsMakeRoomFor(s,1);
        }
        switch(*f) {
        case '%':
            next = *(f+1);
            f++;
            switch(next) {
            case 's':
            case 'S':
                str = va_arg(ap,char*);
                //next如果是s则使用strlen获取长度，否则使用sds的sdslen根据sds的len值去获取长度
                l = (next == 's') ? strlen(str) : sdslen(str);
                if (sdsavail(s) < l) {
                    //如果可以长度小于l长度则扩容
                    s = sdsMakeRoomFor(s,l);
                }
                //复制
                memcpy(s+i,str,l);
                //增加sds字符串长度
                sdsinclen(s,l);
                i += l;
                break;
            case 'i':
            case 'I':
                if (next == 'i')
                    num = va_arg(ap,int);
                else
                    num = va_arg(ap,long long);
                {
                    //SDS_LLSTR_SIZE = 21  char buf[21]
                    char buf[SDS_LLSTR_SIZE];
                    //将long long转成C串
                    l = sdsll2str(buf,num);
                    if (sdsavail(s) < l) {
                        //可用空间小于l则扩容
                        s = sdsMakeRoomFor(s,l);
                    }
                    //复制
                    memcpy(s+i,buf,l);
                    //增加sds字符串长度
                    sdsinclen(s,l);
                    i += l;
                }
                break;
            case 'u':
            case 'U':
                if (next == 'u')
                    unum = va_arg(ap,unsigned int);
                else
                    unum = va_arg(ap,unsigned long long);
                {
                    char buf[SDS_LLSTR_SIZE];
                    //将一个unsigned long long 转换成C字符串格式
                    l = sdsull2str(buf,unum);
                    if (sdsavail(s) < l) {
                        //扩容
                        s = sdsMakeRoomFor(s,l);
                    }
                    memcpy(s+i,buf,l);
                    sdsinclen(s,l);
                    i += l;
                }
                break;
            default: /* Handle %% and generally %<unknown>. */
            //处理%%的情况
                s[i++] = next;
                //增加sds字符串长
                sdsinclen(s,1);
                break;
            }
            break;
        default:
            s[i++] = *f;
            sdsinclen(s,1);
            break;
        }
        f++;
    }
    //设置ap 为NULL
    va_end(ap);
    //sds串末尾置为'\0'
    /* Add null-term */
    s[i] = '\0';
    return s;
}
/* Remove the part of the string from left and from right composed just of
 * contiguous characters found in 'cset', that is a null terminted C string.
 *
 * After the call, the modified sds string is no longer valid and all the
 * references must be substituted with the new pointer returned by the call.
 *
 * Example:
 *
 * s = sdsnew("AA...AA.a.aa.aHelloWorld     :::");
 * s = sdstrim(s,"Aa. :");
 * printf("%s\n", s);
 *
 * Output will be just "HelloWorld".
 */
/**
 * 从sds的头和尾去掉所有和给定字符一致的内容，保留剩下的部分
 * @param s
 * @param cset
 * @return sds
 */
sds sdstrim(sds s, const char *cset) {
    char *start, *end, *sp, *ep;
    size_t len;
    //sp 指向头 ep指向尾
    sp = start = s;
    ep = end = s+sdslen(s)-1;
    // 用于去掉sp头部有参数cset的部分
    while(sp <= end && strchr(cset, *sp)) sp++;
    while(ep > sp && strchr(cset, *ep)) ep--;
    //新的长度
    len = (sp > ep) ? 0 : ((ep-sp)+1);
    //sds拷贝 sp到s
    if (s != sp) memmove(s, sp, len);
    s[len] = '\0';
    //设置sds
    sdssetlen(s,len);
    return s;
}
/* Changes the input string to be a subset of the original.
 * It does not release the free space in the string, so a call to
 * sdsRemoveFreeSpace may be wise after. */
/**
 *
 * @param s
 * @param start
 * @param len
 */
void sdssubstr(sds s, size_t start, size_t len) {
    /* Clamp out of range input */
    //获取sds长度
    size_t oldlen = sdslen(s);
    //如果起始点大于sds长度 则设置start = len = 0
    if (start >= oldlen) start = len = 0;
    //长度如果大于 sds长度-起始点 重新设置长度为 sds长度-起始点
    if (len > oldlen-start) len = oldlen-start;
    //将 s 的 N 个字节复制到 DEST，保证重叠字符串的正确行为。
    /* Move the data */
    if (len) memmove(s, s+start, len);
    s[len] = 0;
    //给sds设置新的长度
    sdssetlen(s,len);
}
/* Turn the string into a smaller (or equal) string containing only the
 * substring specified by the 'start' and 'end' indexes.
 *
 * start and end can be negative, where -1 means the last character of the
 * string, -2 the penultimate character, and so forth.
 *
 * The interval is inclusive, so the start and end characters will be part
 * of the resulting string.
 *
 * The string is modified in-place.
 *
 * NOTE: this function can be misleading and can have unexpected behaviour,
 * specifically when you want the length of the new string to be 0.
 * Having start==end will result in a string with one character.
 * please consider using sdssubstr instead.
 *
 * Example:
 *
 * s = sdsnew("Hello World");
 * sdsrange(s,1,-1); => "ello World"
 */
/**
 * 将sds切片，提供起始和终止位置，可以是负数表示从结尾开始
 * @param s sds字符串
 * @param start 开始
 * @param end 结束
 */
void sdsrange(sds s, ssize_t start, ssize_t end) {
    size_t newlen, len = sdslen(s);
    if (len == 0) return;
    if (start < 0)
        start = len + start;
    if (end < 0)
        end = len + end;
    newlen = (start > end) ? 0 : (end-start)+1;
    sdssubstr(s, start, newlen);
}
/**
 * 将sds的所有字母变成小写，内部是tolower
 * @param s sds
 */
/* Apply tolower() to every character of the sds string 's'. */
void sdstolower(sds s) {
    size_t len = sdslen(s), j;
    for (j = 0; j < len; j++) s[j] = tolower(s[j]);
}
/**
 * 将sds的所有字母变成大写，内部是toupper
 * @param s sds
 */
/* Apply toupper() to every character of the sds string 's'. */
void sdstoupper(sds s) {
    size_t len = sdslen(s), j;
    for (j = 0; j < len; j++) s[j] = toupper(s[j]);
}
/* Compare two sds strings s1 and s2 with memcmp().
 *
 * Return value:
 *
 *     positive if s1 > s2.
 *     negative if s1 < s2.
 *     0 if s1 and s2 are exactly the same binary string.
 *
 * If two strings share exactly the same prefix, but one of the two has
 * additional characters, the longer string is considered to be greater than
 * the smaller one. */
/**
 * 比较两个sds，内部是memcmp
 * @param s1 sds1
 * @param s2 sds2
 * @return
 */
int sdscmp(const sds s1, const sds s2) {
    size_t l1, l2, minlen;
    int cmp;
    //获取sds字符串长度
    l1 = sdslen(s1);
    l2 = sdslen(s2);
    minlen = (l1 < l2) ? l1 : l2;
    /**
     * memcmp
     *  s1 < s2 cmp <0
     *  s1==s2 cmp =0
     *  s1>s2 cmp > 0
     */
    cmp = memcmp(s1,s2,minlen);
    //如果cmp = 0的话 就比较长度
    if (cmp == 0) return l1>l2? 1: (l1<l2? -1: 0);
    return cmp;
}
/* Split 's' with separator in 'sep'. An array
 * of sds strings is returned. *count will be set
 * by reference to the number of tokens returned.
 *
 * On out of memory, zero length string, zero length
 * separator, NULL is returned.
 *
 * Note that 'sep' is able to split a string using
 * a multi-character separator. For example
 * sdssplit("foo_-_bar","_-_"); will return two
 * elements "foo" and "bar".
 *
 * This version of the function is binary-safe but
 * requires length arguments. sdssplit() is just the
 * same function but for zero-terminated strings.
 */
/**
 *
 *  将字符串用指定的分割器分割成若干部分，存入sds指针数组，并返回这个指针数组，是简单的字符串匹配，可以使用KMP优化
 *  输入长度为@len的字符串@s，以及长度为@seplen的字符串@sep。使用@sep对@s进行切分。
 *  切分好的字符串通过返回值@tokens传出，切分得到的个数通过参数@count传出。
 *
 * @param s s字符串
 * @param len 长度
 * @param sep 分隔字符串
 * @param seplen 分隔字符串的长度
 * @param count 分隔后的数组个数
 * @return 返回@tokens
 */
sds *sdssplitlen(const char *s, ssize_t len, const char *sep, int seplen, int *count) {
    int elements = 0, slots = 5;
    long start = 0, j;
    sds *tokens;
    //如果分隔字符串长度小于0 或者要被分割的字符串长度小于0 那么直接返回NULL
    if (seplen < 1 || len < 0) return NULL;
    //分配内存空间
    tokens = s_malloc(sizeof(sds)*slots);
    //如果tokens为NULL 分配内存失败
    if (tokens == NULL) return NULL;
    if (len == 0) {
        *count = 0;
        return tokens;
    }
    for (j = 0; j < (len-(seplen-1)); j++) {
        /* make sure there is room for the next element and the final one */
        //确保预留空间
        if (slots < elements+2) {
            sds *newtokens;
            slots *= 2;
            //分配内存
            newtokens = s_realloc(tokens,sizeof(sds)*slots);
            if (newtokens == NULL) goto cleanup;
            tokens = newtokens;
        }
        /* search the separator */
        /*
         * 两种情况:
         *  1、sep只有一个字符，一个字符一个字符比较，如果相等则进行分割
         *  2、sep是字符串有多个字符，直接用memcmp进行比较，等于0代表相等，每次比较的长度为seplen
         */
        if ((seplen == 1 && *(s+j) == sep[0]) || (memcmp(s+j,sep,seplen) == 0)) {
            //分割字符串
            tokens[elements] = sdsnewlen(s+start,j-start);
            //判断是否分配内存失败，如果失败则goto到cleanup去释放tokens空间
            if (tokens[elements] == NULL) goto cleanup;
            elements++;
            start = j+seplen;
            //跳过分割符
            j = j+seplen-1; /* skip the separator */
        }
    }
    /* Add the final element. We are sure there is room in the tokens array. */
    //最后添加一个元素，确保tokens长度不为0
    tokens[elements] = sdsnewlen(s+start,len-start);
    //判断内存分配是否成功
    if (tokens[elements] == NULL) goto cleanup;
    elements++;
    *count = elements;
    return tokens;
cleanup:
    {
        //释放tokens数组中的元素
        int i;
        for (i = 0; i < elements; i++) sdsfree(tokens[i]);
        s_free(tokens);
        *count = 0;
        return NULL;
    }
}
/**
 * 释放sdssplitlen产生的指针数组和其中的sds的内存
 * @param tokens 分割后得到的数组
 * @param count 数组中元素个数
 */
/* Free the result returned by sdssplitlen(), or do nothing if 'tokens' is NULL. */
void sdsfreesplitres(sds *tokens, int count) {
    if (!tokens) return;
    while(count--)
        sdsfree(tokens[count]);
    s_free(tokens);
}
/* Append to the sds string "s" an escaped string representation where
 * all the non-printable characters (tested with isprint()) are turned into
 * escapes in the form "\n\r\a...." or "\x<hex-number>".
 *
 * After the call, the modified sds string is no longer valid and all the
 * references must be substituted with the new pointer returned by the call. */
/**
 * 处理包含转义字符的二进制字符串
 * @param s
 * @param p
 * @param len
 * @return
 */
sds sdscatrepr(sds s, const char *p, size_t len) {
    //给s字符串后拼接 "\""
    s = sdscatlen(s,"\"",1);
    while(len--) {
        switch(*p) {
        case '\\':
        case '"':
            //将可变长格式化字符串连接到sds后面
            s = sdscatprintf(s,"\\%c",*p);
            break;
        case '\n': s = sdscatlen(s,"\\n",2); break;
        case '\r': s = sdscatlen(s,"\\r",2); break;
        case '\t': s = sdscatlen(s,"\\t",2); break;
        case '\a': s = sdscatlen(s,"\\a",2); break;
        case '\b': s = sdscatlen(s,"\\b",2); break;
        default:
            //检查所传的字符是否是可打印的 可打印为true 否则为false
            if (isprint(*p))
                //将可变长格式化字符串连接到sds后面
                s = sdscatprintf(s,"%c",*p);
            else
                s = sdscatprintf(s,"\\x%02x",(unsigned char)*p);
            break;
        }
        p++;
    }
    //给s字符串后拼接 "\""
    return sdscatlen(s,"\"",1);
}
/**
 * 判断char c是否是十六进制数，是根据ASCII码判断的
 * @param c 字符
 * @return
 */
/* Helper function for sdssplitargs() that returns non zero if 'c'
 * is a valid hex digit. */
int is_hex_digit(char c) {
    return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') ||
           (c >= 'A' && c <= 'F');
}
/**
 * 将一个十六进制字符转换成十进制
 * @param c 字符
 * @return
 */
/* Helper function for sdssplitargs() that converts a hex digit into an
 * integer from 0 to 15 */
int hex_digit_to_int(char c) {
    switch(c) {
    case '0': return 0;
    case '1': return 1;
    case '2': return 2;
    case '3': return 3;
    case '4': return 4;
    case '5': return 5;
    case '6': return 6;
    case '7': return 7;
    case '8': return 8;
    case '9': return 9;
    case 'a': case 'A': return 10;
    case 'b': case 'B': return 11;
    case 'c': case 'C': return 12;
    case 'd': case 'D': return 13;
    case 'e': case 'E': return 14;
    case 'f': case 'F': return 15;
    default: return 0;
    }
}
/* Split a line into arguments, where every argument can be in the
 * following programming-language REPL-alike form:
 *
 * foo bar "newline are supported\n" and "\xff\x00otherstuff"
 *
 * The number of arguments is stored into *argc, and an array
 * of sds is returned.
 *
 * The caller should free the resulting array of sds strings with
 * sdsfreesplitres().
 *
 * Note that sdscatrepr() is able to convert back a string into
 * a quoted string in the same format sdssplitargs() is able to parse.
 *
 * The function returns the allocated tokens on success, even when the
 * input string is empty, or NULL if the input contains unbalanced
 * quotes or closed quotes followed by non space characters
 * as in: "foo"bar or "foo'
 */
/**
 * 字符串分割函数
 * 将一行内容读取到sds指针数组，解析配置文件时使用，每个配置项保存在一个sds中，此函数返回一个sds指针数组和其元素个数
 * @param line
 * @param argc
 * @return
 */
sds *sdssplitargs(const char *line, int *argc) {
    const char *p = line;
    char *current = NULL;
    char **vector = NULL;
    *argc = 0;
    while(1) {
        /* skip blanks */
        // isspace 判断字符是否为空白字符  不是空白字符  返回0 ,是空白字符    返回非0
        while(*p && isspace(*p)) p++;
        if (*p) {
            /* get a token */
            int inq=0;  /* set to 1 if we are in "quotes" */
            int insq=0; /* set to 1 if we are in 'single quotes' */
            int done=0;
            //如果curent为NULL则创建一个空的sds字符串
            if (current == NULL) current = sdsempty();
            while(!done) {
                // *p = '"' inq = 1
                //处理单引号
                if (inq) {
                    //处理16进制数字转换
                    // 如果满足 *p == '\\'  *(p+1) == 'x' 和 *(p+2)、*(p+3)都是十六进制
                    if (*p == '\\' && *(p+1) == 'x' &&
                                             is_hex_digit(*(p+2)) &&
                                             is_hex_digit(*(p+3)))
                    {
                        unsigned char byte;
                        // 16进制转10进制
                        byte = (hex_digit_to_int(*(p+2))*16)+
                                hex_digit_to_int(*(p+3));
                        current = sdscatlen(current,(char*)&byte,1);
                        p += 3;
                    } else if (*p == '\\' && *(p+1)) {
                        //处理特殊字符
                        char c;
                        p++;
                        switch(*p) {
                        case 'n': c = '\n'; break;
                        case 'r': c = '\r'; break;
                        case 't': c = '\t'; break;
                        case 'b': c = '\b'; break;
                        case 'a': c = '\a'; break;
                        default: c = *p; break;
                        }
                        current = sdscatlen(current,&c,1);
                    } else if (*p == '"') {
                        /* closing quote must be followed by a space or
                         * nothing at all. */
                        if (*(p+1) && !isspace(*(p+1))) goto err;
                        done=1;
                    } else if (!*p) {
                        /* unterminated quotes */
                        goto err;
                    } else {
                        current = sdscatlen(current,p,1);
                    }
                } else if (insq) {
                    //处理单引号
                    if (*p == '\\' && *(p+1) == '\'') {
                        p++;
                        current = sdscatlen(current,"'",1);
                    } else if (*p == '\'') {
                        /* closing quote must be followed by a space or
                         * nothing at all. */
                        if (*(p+1) && !isspace(*(p+1))) goto err;
                        done=1;
                    } else if (!*p) {
                        /* unterminated quotes */
                        goto err;
                    } else {
                        current = sdscatlen(current,p,1);
                    }
                } else {
                    switch(*p) {
                    case ' ':
                    case '\n':
                    case '\r':
                    case '\t':
                    case '\0':
                        done=1;
                        break;
                    case '"':
                        inq=1;
                        break;
                    case '\'':
                        insq=1;
                        break;
                    default:
                        //拼接到curent后面
                        current = sdscatlen(current,p,1);
                        break;
                    }
                }
                if (*p) p++;
            }
            //分配内存空间
            /* add the token to the vector */
            vector = s_realloc(vector,((*argc)+1)*sizeof(char*));
            vector[*argc] = current;
            (*argc)++;
            current = NULL;
        } else {
            /* Even on empty input string return something not NULL. */
            //即使输入为空也返回不为空的内容
            if (vector == NULL) vector = s_malloc(sizeof(void*));
            return vector;
        }
    }
err:
    while((*argc)--)
        sdsfree(vector[*argc]);
    s_free(vector);
    if (current) sdsfree(current);
    *argc = 0;
    return NULL;
}
/* Modify the string substituting all the occurrences of the set of
 * characters specified in the 'from' string to the corresponding character
 * in the 'to' array.
 *
 * For instance: sdsmapchars(mystring, "ho", "01", 2)
 * will have the effect of turning the string "hello" into "0ell1".
 *
 * The function returns the sds string pointer, that is always the same
 * as the input pointer since no resize is needed. */
/**
 * 将sds中出现在指定字符集中的字符用另一个字符集中的字符代替，要求两个字符集长度相等
 * @param s sds字符串
 * @param from 指定的字符
 * @param to 替换成的字符
 * @param setlen 长度
 * @return sds
 */
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen) {
    size_t j, i, l = sdslen(s);
    for (j = 0; j < l; j++) {
        for (i = 0; i < setlen; i++) {
            if (s[j] == from[i]) {
                s[j] = to[i];
                break;
            }
        }
    }
    return s;
}
/* Join an array of C strings using the specified separator (also a C string).
 * Returns the result as an sds string. */
/**
 * 将若干C字符串用提供的分割器连接起来，产生一个sds
 * @param argv C字符串
 * @param argc 个数
 * @param sep 分割符
 * @return
 */
sds sdsjoin(char **argv, int argc, char *sep) {
    sds join = sdsempty();
    int j;
    for (j = 0; j < argc; j++) {
        //字符串拼接到join后面
        join = sdscat(join, argv[j]);
        if (j != argc-1) join = sdscat(join,sep);
    }
    return join;
}
/**
 * 和sdsjoin类似，连接的是若干sds
 * @param argv 若干个sds字符串
 * @param argc 个数
 * @param sep 分隔符
 * @param seplen 长度
 * @return
 */
/* Like sdsjoin, but joins an array of SDS strings. */
sds sdsjoinsds(sds *argv, int argc, const char *sep, size_t seplen) {
    sds join = sdsempty();
    int j;
    for (j = 0; j < argc; j++) {
        join = sdscatsds(join, argv[j]);
        if (j != argc-1) join = sdscatlen(join,sep,seplen);
    }
    return join;
}
/* Wrappers to the allocators used by SDS. Note that SDS will actually
 * just use the macros defined into sdsalloc.h in order to avoid to pay
 * the overhead of function calls. Here we define these wrappers only for
 * the programs SDS is linked to, if they want to touch the SDS internals
 * even if they use a different allocator. */
/**
 * 分配内存
 * @param size
 * @return
 */
void *sds_malloc(size_t size) { return s_malloc(size); }
/**
 * 重新分配内存
 * @param ptr
 * @param size
 * @return
 */
void *sds_realloc(void *ptr, size_t size) { return s_realloc(ptr,size); }
/**
 * 释放内存
 * @param ptr
 */
void sds_free(void *ptr) { s_free(ptr); }
/* Perform expansion of a template string and return the result as a newly
 * allocated sds.
 *
 * Template variables are specified using curly brackets, e.g. {variable}.
 * An opening bracket can be quoted by repeating it twice.
 */
/**
 * sds回调模板函数
 * @param template
 * @param cb_func
 * @param cb_arg
 * @return
 */
sds sdstemplate(const char *template, sdstemplate_callback_t cb_func, void *cb_arg)
{
    sds res = sdsempty();
    const char *p = template;
    while (*p) {
        /* Find next variable, copy everything until there */
        const char *sv = strchr(p, '{');
        if (!sv) {
            /* Not found: copy till rest of template and stop */
            res = sdscat(res, p);
            break;
        } else if (sv > p) {
            /* Found: copy anything up to the begining of the variable */
            res = sdscatlen(res, p, sv - p);
        }
        /* Skip into variable name, handle premature end or quoting */
        //跳过遍历名称
        sv++;
        if (!*sv) goto error;       /* Premature end of template */
        if (*sv == '{') {
            /* Quoted '{' */
            p = sv + 1;
            res = sdscat(res, "{");
            continue;
        }
        /* Find end of variable name, handle premature end of template */
        const char *ev = strchr(sv, '}');
        if (!ev) goto error;
        /* Pass variable name to callback and obtain value. If callback failed,
         * abort. */
        // 通过变量名称去回调
        sds varname = sdsnewlen(sv, ev - sv);
        sds value = cb_func(varname, cb_arg);
        //释放内存空间
        sdsfree(varname);
        if (!value) goto error;
        //将值添加到结果
        /* Append value to result and continue */
        res = sdscat(res, value);
        //释放值
        sdsfree(value);
        p = ev + 1;
    }
    return res;
error:
    //释放res
    sdsfree(res);
    return NULL;
}
#ifdef REDIS_TEST
#include <stdio.h>
#include <limits.h>
#include "testhelp.h"
#define UNUSED(x) (void)(x)
static sds sdsTestTemplateCallback(sds varname, void *arg) {
    UNUSED(arg);
    static const char *_var1 = "variable1";
    static const char *_var2 = "variable2";
    if (!strcmp(varname, _var1)) return sdsnew("value1");
    else if (!strcmp(varname, _var2)) return sdsnew("value2");
    else return NULL;
}
int sdsTest(int argc, char **argv, int accurate) {
    UNUSED(argc);
    UNUSED(argv);
    UNUSED(accurate);
    {
        sds x = sdsnew("foo"), y;
        test_cond("Create a string and obtain the length",
            sdslen(x) == 3 && memcmp(x,"foo\0",4) == 0);
        sdsfree(x);
        x = sdsnewlen("foo",2);
        test_cond("Create a string with specified length",
            sdslen(x) == 2 && memcmp(x,"fo\0",3) == 0);
        x = sdscat(x,"bar");
        test_cond("Strings concatenation",
            sdslen(x) == 5 && memcmp(x,"fobar\0",6) == 0);
        x = sdscpy(x,"a");
        test_cond("sdscpy() against an originally longer string",
            sdslen(x) == 1 && memcmp(x,"a\0",2) == 0);
        x = sdscpy(x,"xyzxxxxxxxxxxyyyyyyyyyykkkkkkkkkk");
        test_cond("sdscpy() against an originally shorter string",
            sdslen(x) == 33 &&
            memcmp(x,"xyzxxxxxxxxxxyyyyyyyyyykkkkkkkkkk\0",33) == 0);
        sdsfree(x);
        x = sdscatprintf(sdsempty(),"%d",123);
        test_cond("sdscatprintf() seems working in the base case",
            sdslen(x) == 3 && memcmp(x,"123\0",4) == 0);
        sdsfree(x);
        x = sdscatprintf(sdsempty(),"a%cb",0);
        test_cond("sdscatprintf() seems working with \\0 inside of result",
            sdslen(x) == 3 && memcmp(x,"a\0""b\0",4) == 0);
        {
            sdsfree(x);
            char etalon[1024*1024];
            for (size_t i = 0; i < sizeof(etalon); i++) {
                etalon[i] = '0';
            }
            x = sdscatprintf(sdsempty(),"%0*d",(int)sizeof(etalon),0);
            test_cond("sdscatprintf() can print 1MB",
                sdslen(x) == sizeof(etalon) && memcmp(x,etalon,sizeof(etalon)) == 0);
        }
        sdsfree(x);
        x = sdsnew("--");
        x = sdscatfmt(x, "Hello %s World %I,%I--", "Hi!", LLONG_MIN,LLONG_MAX);
        test_cond("sdscatfmt() seems working in the base case",
            sdslen(x) == 60 &&
            memcmp(x,"--Hello Hi! World -9223372036854775808,"
                     "9223372036854775807--",60) == 0);
        printf("[%s]\n",x);
        sdsfree(x);
        x = sdsnew("--");
        x = sdscatfmt(x, "%u,%U--", UINT_MAX, ULLONG_MAX);
        test_cond("sdscatfmt() seems working with unsigned numbers",
            sdslen(x) == 35 &&
            memcmp(x,"--4294967295,18446744073709551615--",35) == 0);
        sdsfree(x);
        x = sdsnew(" x ");
        sdstrim(x," x");
        test_cond("sdstrim() works when all chars match",
            sdslen(x) == 0);
        sdsfree(x);
        x = sdsnew(" x ");
        sdstrim(x," ");
        test_cond("sdstrim() works when a single char remains",
            sdslen(x) == 1 && x[0] == 'x');
        sdsfree(x);
        x = sdsnew("xxciaoyyy");
        sdstrim(x,"xy");
        test_cond("sdstrim() correctly trims characters",
            sdslen(x) == 4 && memcmp(x,"ciao\0",5) == 0);
        y = sdsdup(x);
        sdsrange(y,1,1);
        test_cond("sdsrange(...,1,1)",
            sdslen(y) == 1 && memcmp(y,"i\0",2) == 0);
        sdsfree(y);
        y = sdsdup(x);
        sdsrange(y,1,-1);
        test_cond("sdsrange(...,1,-1)",
            sdslen(y) == 3 && memcmp(y,"iao\0",4) == 0);
        sdsfree(y);
        y = sdsdup(x);
        sdsrange(y,-2,-1);
        test_cond("sdsrange(...,-2,-1)",
            sdslen(y) == 2 && memcmp(y,"ao\0",3) == 0);
        sdsfree(y);
        y = sdsdup(x);
        sdsrange(y,2,1);
        test_cond("sdsrange(...,2,1)",
            sdslen(y) == 0 && memcmp(y,"\0",1) == 0);
        sdsfree(y);
        y = sdsdup(x);
        sdsrange(y,1,100);
        test_cond("sdsrange(...,1,100)",
            sdslen(y) == 3 && memcmp(y,"iao\0",4) == 0);
        sdsfree(y);
        y = sdsdup(x);
        sdsrange(y,100,100);
        test_cond("sdsrange(...,100,100)",
            sdslen(y) == 0 && memcmp(y,"\0",1) == 0);
        sdsfree(y);
        y = sdsdup(x);
        sdsrange(y,4,6);
        test_cond("sdsrange(...,4,6)",
            sdslen(y) == 0 && memcmp(y,"\0",1) == 0);
        sdsfree(y);
        y = sdsdup(x);
        sdsrange(y,3,6);
        test_cond("sdsrange(...,3,6)",
            sdslen(y) == 1 && memcmp(y,"o\0",2) == 0);
        sdsfree(y);
        sdsfree(x);
        x = sdsnew("foo");
        y = sdsnew("foa");
        test_cond("sdscmp(foo,foa)", sdscmp(x,y) > 0);
        sdsfree(y);
        sdsfree(x);
        x = sdsnew("bar");
        y = sdsnew("bar");
        test_cond("sdscmp(bar,bar)", sdscmp(x,y) == 0);
        sdsfree(y);
        sdsfree(x);
        x = sdsnew("aar");
        y = sdsnew("bar");
        test_cond("sdscmp(bar,bar)", sdscmp(x,y) < 0);
        sdsfree(y);
        sdsfree(x);
        x = sdsnewlen("\a\n\0foo\r",7);
        y = sdscatrepr(sdsempty(),x,sdslen(x));
        test_cond("sdscatrepr(...data...)",
            memcmp(y,"\"\\a\\n\\x00foo\\r\"",15) == 0);
        {
            unsigned int oldfree;
            char *p;
            int i;
            size_t step = 10, j;
            sdsfree(x);
            sdsfree(y);
            x = sdsnew("0");
            test_cond("sdsnew() free/len buffers", sdslen(x) == 1 && sdsavail(x) == 0);
            /* Run the test a few times in order to hit the first two
             * SDS header types. */
            for (i = 0; i < 10; i++) {
                size_t oldlen = sdslen(x);
                x = sdsMakeRoomFor(x,step);
                int type = x[-1]&SDS_TYPE_MASK;
                test_cond("sdsMakeRoomFor() len", sdslen(x) == oldlen);
                if (type != SDS_TYPE_5) {
                    test_cond("sdsMakeRoomFor() free", sdsavail(x) >= step);
                    oldfree = sdsavail(x);
                    UNUSED(oldfree);
                }
                p = x+oldlen;
                for (j = 0; j < step; j++) {
                    p[j] = 'A'+j;
                }
                sdsIncrLen(x,step);
            }
            test_cond("sdsMakeRoomFor() content",
                memcmp("0ABCDEFGHIJABCDEFGHIJABCDEFGHIJABCDEFGHIJABCDEFGHIJABCDEFGHIJABCDEFGHIJABCDEFGHIJABCDEFGHIJABCDEFGHIJ",x,101) == 0);
            test_cond("sdsMakeRoomFor() final length",sdslen(x)==101);
            sdsfree(x);
        }
        /* Simple template */
        x = sdstemplate("v1={variable1} v2={variable2}", sdsTestTemplateCallback, NULL);
        test_cond("sdstemplate() normal flow",
                  memcmp(x,"v1=value1 v2=value2",19) == 0);
        sdsfree(x);
        /* Template with callback error */
        x = sdstemplate("v1={variable1} v3={doesnotexist}", sdsTestTemplateCallback, NULL);
        test_cond("sdstemplate() with callback error", x == NULL);
        /* Template with empty var name */
        x = sdstemplate("v1={", sdsTestTemplateCallback, NULL);
        test_cond("sdstemplate() with empty var name", x == NULL);
        /* Template with truncated var name */
        x = sdstemplate("v1={start", sdsTestTemplateCallback, NULL);
        test_cond("sdstemplate() with truncated var name", x == NULL);
        /* Template with quoting */
        x = sdstemplate("v1={{{variable1}} {{} v2={variable2}", sdsTestTemplateCallback, NULL);
        test_cond("sdstemplate() with quoting",
                  memcmp(x,"v1={value1} {} v2=value2",24) == 0);
        sdsfree(x);
    }
    test_report();
    return 0;
}
#endif