习题4.6：复制空洞文件但不写入0

 本文转自：http://blog.youkuaiyun.com/happyangel_xl/archive/2009/07/26/4382218.aspx

程序：

/*
    copy hole files without filling the hole with char 0
*/

#include "apue.h"
#include <fcntl.h>

#define BUFFSIZE 4096       

int main(int argc, char* argv[])
{
    char buf[BUFFSIZE];
    int i;
    int fdsrc, fddst;  //source/destination  file description
    off_t offset;
    int real;          //start position to be copied
    int n;

    if(argc != 3)
        err_quit("usage: mycp src dst/n");

    if((fdsrc = open(argv[1], O_RDONLY)) < 0)
        err_ret("%s: open error", argv[1]);
    if((fddst = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, FILE_MODE)) < 0)
        err_ret("%s: open error", argv[2]);
    offset = 0; 

    while((n = read(fdsrc, buf, BUFFSIZE)) > 0){
        for(i=0; i < n; i++){
            real = i;
            while(buf[i] != 0 && i < n)
                i++;   //test where there are no zero char and record
            if(i != real){
                if(lseek(fddst, offset+real, SEEK_SET) == -1)
                    err_sys("lseek error/n");
                if(write(fddst, buf, i-real) != (i-real))
                    err_sys("write error/n");
            }
        }
        offset += n;  //reset offset
    }
    if(n < 0)
        err_sys("read error");

    exit(0);
}