APUE 习题3-2 实现dup2，要求不使用fcntl函数。
int mydup2(int oldfd, int newfd)
{
int tfd = 0;
if (newfd < 0)
{
err_sys("newfd < 0");
}
if (newfd == oldfd)
{
return oldfd;
}
while(1)
{
tfd = dup(oldfd);
if (tfd == newfd)
{
return newfd;
}
else if (tfd > newfd)
{
close(newfd);
}
}
}
测试：
#include "apue.h"
#include <fcntl.h>
int mydup2(int oldfd, int newfd);
int main(void)
{
int fd = 0;
fd = open("testdup2.dat", O_RDWR | O_CREAT | O_TRUNC);
if (fd < 0)
{
printf("open error.\n");
return -1;
}
if (mydup2(fd, STDOUT_FILENO) < 0)
{
printf("mydup2 error\n");
return -1;
}
printf("slk\n");
return 0;
}
int mydup2(int oldfd, int newfd)
{
int tfd = 0;
if (newfd < 0)
{
err_sys("newfd < 0");
}
if (newfd == oldfd)
{
return oldfd;
}
while(1)
{
tfd = dup(oldfd);
if (tfd == newfd)
{
return newfd;
}
else if (tfd > newfd)
{
close(newfd);
}
}
}
可以把输出重定向到testdup2.dat，成功
