apue 习题4.6参考答案

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

int
main(int argc, char *argv[])
{
if(argc != 3)
err_sys("usage: ./EX_4_6.o <src path> <dst path>");

char *src_path = argv[1];
char *dst_path = argv[2];

int fd = open(src_path, O_RDWR);
int fd2 = open(dst_path, O_WRONLY);

int n;
char buf[100] = "1234567890123456789";
char buf2;

/* 给源文件制造空洞，结束后将源文件偏移量设为0 */

int offset = lseek(fd, 100, SEEK_SET);
printf("offset of src is %d\n", offset);
printf("the buf is %s\n", buf);
if(write(fd, buf, 100) < 0)
err_sys("write to source file error.");
lseek(fd, 0, SEEK_SET);

/* 将源文件内容复制到目标文件 */
while((n = read(fd, &buf2, 1)) == 1)
{
/* 如果读到'\0'，则不复制 */
if(buf2 == '\0')
continue;
if(write(fd2, &buf2, 1) != 1)
err_sys("write error.");
}

if(n < 0)
err_sys("read error.");

close(fd);
close(fd2);
exit(0);
}

/* source */
xxx@xxx:~/Desktop/apue_demo/file_dir$ od -c foo　
0000000   1   2   3   3   4   5   5  \n  \0  \0  \0  \0  \0  \0  \0  \0
0000020  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0000140  \0  \0  \0  \0   1   2   3   4   5   6   7   8   9   0   1   2
0000160   3   4   5   6   7   8   9  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000200  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0000300  \0  \0  \0  \0  \0  \0  \0  \0
0000310
/* dest */
xxx@xxx:~/Desktop/apue_demo/file_dir$ od -c bar
0000000   1   2   3   3   4   5   5  \n   1   2   3   4   5   6   7   8
0000020   9   0   1   2   3   4   5   6   7   8   9
0000033