p4-10.c

UNIX程序设计教程

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include "err_exit.h"
int main(int argc, char*argv[])
{  
    int length;
    int fd;
    /* 检查参数的正确性 */
    if (argc != 3){
       printf("usage: a.out <filename> <integer unmber>\n");
       exit(1);
    }
    /* 读取参数并打开文件 */
    length = atoi(argv[2]);
    if ((fd = open(argv[1],O_RDWR)) < 0)
       err_exit("open() call failed");
    /* 按第二参数指定字节截断文件 */
    printf ("truncate %s to %d characaters\n", argv[1], length);
    if ( ftruncate(fd, length) < 0 ) 
       err_exit("truncate() call failed");
    printf ("truncate() call successful\n");
    /* 在截断后的文件尾部写入尾部标识 */
    lseek(fd,(long)0, SEEK_END);
    write(fd, "#here is tail.",14);
    close(fd);
}