15.1 标准I/O函数的优点

15.1.1 标准I/O函数的两个优点

• 标准I/O函数具有良好的移植性
• 标准I/O函数可以利用缓冲提高性能

关于良好的移植性这一点要强调，所有的标准函数都具有良好的移植性。

15.1.2 标准I/O函数的系统函数之间的性能对比

//syscpy.c
#include<stdio.h>
#include<fcntl.h>
#define BUF_SIZE 3
int main(int argc, char *argv[])
{
    int fd1, fd2;
    int len;
    char buf[BUF_SIZE];
    fd1=open("news.txt", O_RDONLY);
    fd2=open("cpy.txt", O_WRONLY|O_CREAT|O_TRUNC);
    while((len=read(fd1, buf, sizeof(buf)))>0)
        write(fd2, buf, len);
    close(fd1);
    close(fd2);
    return 0;
}

//stdcpy.c
#include<stdio.h>
#define BUF_SIZE 3

int main(int argc, char *argv[])
{
    FILE *fp1;
    FILE *fp2;
    char buf[BUF_SIZE];

    fp1=fopen("news.txt", "r");
    fp2=fopen("cpy.txt", "w");

    while(fgets(buf, BUF_SIZE, fp1)!=NULL)
        fputs(buf, fp2);

    fclose(fp1);
    fclose(fp2);
    return 0;
}

15.1.3 标准I/O函数的几个缺点

• 不容易进行双向通信
• 有时可能频繁调用fflush函数
• 需要以FILE结构体指针的形式返回文件描述符

15.2 使用标准I/O函数

15.2.1 利用fdopen函数转换为FILE结构体指针

#include<stdio.h>
FILE *fdopen(int fildes, const char *mode);
//成功时返回转换的FILE结构体指针，失败时返回NULL
//fildes需要转换的文件描述符
//mode将要创建的FILE结构体指针的模式（mode）信息

//desto.c
#include<stdio.h>
#include<fcntl.h>

int main(void)
{
    FILE *fp;
    int fd=open("data.dat",  O_WRONLY|O_CREAT|O_TRUNC);
    if(fd==-1)
    {
        fputs("file open error", stdout);
        return -1;
    }

    fd=fdopen(fd, "w");
    fputs("Network C programming \n", fp);
    fclose(fp);
    return 0;
}

15.2.2 利用fileno函数转换为文件描述符

#include<stdio.h>

int fileno(FILE *stream);
//成功时返回转换后的文件描述符，失败时返回-1

//todes.c
#include<stdio.h>
#include<fcntl.h>

int main(void)
{
    FILE *fp;
    int fd=open("data.dat",  O_WRONLY|O_CREAT|O_TRUNC);
    if(fd==-1)
    {
        fputs("file open error", stdout);
        return -1;
    }

    printf("First file descriptor: %d\n", fd);
    fp=fdopen(fd, "w");
    fputs("TCP/IP SOCKET PROGRAMMING \n", fp);
    printf("Second file descriptor: %d \n", fileno(fp));
    fclose(fp);
    return 0;
}

15.3 基于套接字的标准I/O函数使用

//echo_stdserv.c
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<sys/socket.h>

#define BUF_SIZE 1024
void error_handling(char *message);

int main(int argc, char *argv[])
{
    int serv_sock, clnt_sock;
    char message[BUF_SIZE];
    int str_len, i;

    struct sockaddr_in serv_adr, clnt_adr;
    socklen_t clnt_adr_sz;
    FILE *readfp;
    FILE *writefp;

    if(argc!=2){
        printf("Usage : %s<port>\n", argv[0]);
        exit(1);
    }

    serv_sock = socket(PF_INET, SOCK_STREAM, 0);
    if(serv_sock==-1)
        error_handling("socket() error");

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family=AF_INET;
    serv_adr.sin_addr.s_addr=htonl(INADDR_ANY);
    serv_adr.sin_port=htons(atoi(argv[1]));

    if(bind(serv_sock, (struct sockaddr*)&serv_adr,sizeof(serv_adr))==-1)
        error_handling("bind() error");

    if(listen(serv_sock, 5)==-1)
        error_handling("listen() error");

    clnt_adr_sz=sizeof(clnt_adr);
    for(i=0; i<5; i++)
    {
        clnt_sock=accept(serv_sock, (struct sockaddr*)&clnt_adr, &clnt_adr_sz);
        if(clnt_sock==-1)
            error_handling("accept() error");
        else
            printf("Connected client %d \n", i+1);
        readfp=fdopen(clnt_sock, "r");
        writefp=fdopen(clnt_sock, "w");
        while(!feof(readfp))
        {
            fgets(message, BUF_SIZE, readfp);
            fputs(message, writefp);
            fflush(writefp);
        }
        fclose(readfp);
        fclose(writefp);
    }
    close(serv_sock);
    return 0;
}

void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

//echo_client.c
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<sys/socket.h>

#define BUF_SIZE 1024
void error_handling(char *message);
int main(int argc, char *argv[])
{
    int sock;
    char message[BUF_SIZE];
    int str_len;
    struct sockaddr_in serv_adr;
    FILE *readfp;
    FILE *writefp;
    if(argc!=3){
        printf("Usage : %s <IP> <port>\n", argv[0]);
        exit(1);
    }

    sock=socket(PF_INET, SOCK_STREAM, 0);
    if(sock==-1)
        error_handling("socket() error");

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family=AF_INET;
    serv_adr.sin_addr.s_addr=inet_addr(argv[1]);
    serv_adr.sin_port=htons(atoi(argv[2]));

    if(connect(sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr))==-1)
        error_handling("connect() error!");
    else
        puts("Connected.........");

    readfp=fdopen(sock, "r");
    writefp=fdopen(sock, "w");
    while(1)
    {
        fputs("Input message(Q to quit):", stdout);
        fgets(message, BUF_SIZE, stdin);

        if(!strcmp(message,"q\n")||!strcmp(message,"Q\n"))
            break;

        fputs(message, writefp);
        fflush(writefp);
        fgets(message, BUF_SIZE, readfp);
        printf("Message from server: %s", message);
    }
    fclose(writefp);
    fclose(readfp);
    return 0;
}
void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

#server
zhang@zhang-virtual-machine:~/Desktop/Ctest/Demo31$ ./echo_stdserv 9190
Connected client 1 
#client
zhang@zhang-virtual-machine:~/Desktop/Ctest/Demo31$ ./echo_client 127.0.0.1 9190
Connected.........
Input message(Q to quit):das
Message from server: das
Input message(Q to quit):q