p3-6-7.c

UNIX程序设计教程

#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include "err_exit.h"
#define STDIN_FILENO 0
#define STDOUT_FILENO 1
char buf[100000];
/* 如果value非0，设置desc的O_NONBLOCK标志,否则清除该标志。成功返回0，失败返回-1.*/
int set_nonblock_flag (int desc, int value)
{
    int oldflags = fcntl(desc, F_GETFL, 0);
    /* 获取标签失败，返回错误指示. */
    if (oldflags == -1)
        return -1;
     /* 形成我们需要的标签. */
    if (value != 0)
        oldflags |= O_NONBLOCK;
    else
        oldflags &= ~O_NONBLOCK;
    /* 设置新标签. */
    return fcntl(desc, F_SETFL, oldflags);
}

int main(void)
{
    int totalbytes, nwrite;
    char *ptr;
    int ntimes = 0;
    /* 从标准输入一次读入100000字节数据 */
    totalbytes = read(STDIN_FILENO,buf,sizeof(buf));
    fprintf(stderr,"read %d bytes\n", totalbytes);
    /* 设置无阻塞I/O */
    if (set_nonblock_flag(STDOUT_FILENO, 1) < 0)         
        err_exit("set nonblock flag failed ");   
    /* 将buf中的数据写至标准输出，直至全部写出 */
    for (ptr = buf; totalbytes >0; ntimes++){
        errno = 0;
        nwrite = write(STDOUT_FILENO,ptr, totalbytes);
        if (nwrite < 0){
               fprintf(stderr,"%d  nwrite = %d,error = %d, ",ntimes,nwrite,errno);
               perror("");
        }
        else {
            fprintf(stderr,"%d  nwrite = %d,error = %d\n",ntimes,nwrite,errno);
            ptr += nwrite;
            totalbytes -= nwrite;
        }
    }
    /* 恢复阻塞方式 */
    if (set_nonblock_flag(STDOUT_FILENO, 0) < 0)    
        err_exit ("clear nonblock flag failed"); 
    exit(0);
}