C嵌入式提高篇

1.变量的存放位置

注意：volatile
volatile是一个特征修饰符（type specifier）.volatile的作用是作为指令关键字，确保本条指令不会因编译器的优化而省略，且要求每次直接读值。

2.结构体的存在空间

#include<stdio.h>
#include<string.h>
#include <stdlib.h>
struct person {
    char* name;
    int age;
};
struct person2 {
    char name[100];
    int age;
};
struct person3 {
    char sex;
    int age;
};
struct person4 {
    char sex;
    char high;
    int age;
};
struct company {
    char* name;
    struct person worker[100];
};
int main(void)
{
    struct person wei = { "weidongshan", 40 };
    printf("sizeof(int) = %d, sizeof(char) = %d\r\n", sizeof(int), sizeof(char));
    printf("sizeof(int *) = %d, sizeof(char *) = %d\r\n", sizeof(int*), sizeof(char*));
    printf("sizeof(struct person) = %d, sizeof(struct person2) = %d\r\n", \
        sizeof(struct person), sizeof(struct person2));
    printf("sizeof(struct person *) = %d, sizeof(struct person2 *) = %d\r\n", \
        sizeof(struct person*), sizeof(struct person2*));
    printf("sizeof(struct person3) = %d, sizeof(struct person3 *) = %d\r\n", \
        sizeof(struct person3), sizeof(struct person3*));
    printf("sizeof(struct person4) = %d, sizeof(struct person4 *) = %d\r\n", \
        sizeof(struct person4), sizeof(struct person4*));
    printf("name = %s, age = %d\r\n", wei.name, wei.age);
    while (1);
    return 0;
}

3.结构体的存在空间

#include<stdio.h>
#include<string.h>
#include <stdlib.h>
typedef struct student {
    char* name;
    int age;
    struct student* classmate;
}student, * pstudent;
int main(void)
{
    student zhangsan = { "zhangshan", 10, NULL };
    student lili = { "lili", 10, NULL };
    zhangsan.classmate = &lili;
    lili.classmate = &zhangsan;
    printf("zhangsan's classmate is :%s\r\n", zhangsan.classmate->classmate->classmate->name);
    while (1);
    return 0;
}

4.函数指针

#include<stdio.h>
#include<string.h>
#include <stdlib.h>
typedef struct student {
    char* name;
    int age;
    void (*good_work)(void);
    struct student* classmate;
}student, * pstudent;
static void play_ball(void)
{
    printf("playing ball\r\n");
}
static void sing_song(void)
{
    printf("singing\r\n");
}
int main(void)
{
    int i;
    //函数有特权可以不加取址符号
    student ss[2] = { {"zhangshan", 10, &play_ball, NULL}, {"lili", 10, sing_song, NULL} };
    for (i = 0; i < 2; i++)
    {
        ss[i].good_work();
    }
    while (1);
    return 0;
}

5.函数指针的使用

#include<stdio.h>
#include<string.h>
#include <stdlib.h>
typedef struct lcd_operation {
    int type;
    void (*draw_logo)(void);
}lcd_operation, * p_lcd_operation;
int read_eeprom()
{
    /* 0: lcd a
     * 1: lcd b
     */
    return 0;
}
int get_lcd_type(void)
{
    return read_eeprom();
}
void draw_logo_lcda(void)
{
    printf("display logo on lcd a\r\n");
}
void draw_logo_lcdb(void)
{
    printf("display logo on lcd b\r\n");
}
lcd_operation xxx_com_lcds[2] = {
    {0, draw_logo_lcda},
    {1, draw_logo_lcdb},
};
p_lcd_operation get_lcd(void)
{
    int type = get_lcd_type();
    return &xxx_com_lcds[type];
}
//结构体成员的初始化
lcd_operation lcd_a_ops = {
    .type = 0,
    .draw_logo = draw_logo_lcda,
}; 
//add_type是个函数指针，返回值为int，参数为(int,int)
typedef int (*add_type)(int, int);
add_type f1;
add_type f2;
int (*f3)(int, int);
int (*f4)(int, int);
int main(void)
{
    p_lcd_operation lcd;
    lcd = get_lcd();
    lcd->draw_logo();
    while (1);
    return 0;
}

6.单向链表的使用

#include<stdio.h>
#include<string.h>
#include <stdlib.h>
typedef struct spy {
    char* name;
    struct spy* next;
}spy, * p_spy;
spy A = { "A", NULL };
spy B = { "B", NULL };
spy C = { "C", NULL };
spy D = { "D", NULL };
spy E = { "E", NULL };
p_spy head = NULL;
//链表的尾插法
void insert_spy(p_spy newspy)
{
    p_spy last;
    if (head == NULL)
    {
        head = newspy;
        newspy->next = NULL;
    }
    else
    {
        /* 先找到链表的最后一项 last */
        last = head;
        while (last)
        {
            if (last->next == NULL) /* 找到了 */
                break;
            else
                last = last->next;
        }
        /*  */
        last->next = newspy;
        newspy->next = NULL;
    }
}
//链表的删除
void remove_spy(p_spy oldspy)
{
    p_spy left;
    if (head == oldspy)
    {
        head = oldspy->next;
    }
    else
    {
        /* 找出oldspy的上线 */
        left = head;
        while (left)
        {
            if (left->next == oldspy)
                break;
            else
                left = left->next;
        }
        if (left)
        {
            left->next = oldspy->next;
        }
    }
}
void print_spy(void)
{
    p_spy tmp = head;
    while (tmp)
    {
        printf("%s\r\n", tmp->name);
        tmp = tmp->next;
    }
}
int main(void)
{
    /*
        A.next = &B;
        B.next = &C;
        C.next = NULL;
    */
    insert_spy(&A);
    insert_spy(&B);
    insert_spy(&C);
    insert_spy(&D);
    head = &A;
    print_spy();
    remove_spy(&D);
    printf("remove spy B: \r\n");
    print_spy();
    system("pause");
    return 0;
}