dup2文件描述符重定向

#include

int dup2(int oldfd, int newfd);

 

The error returned by dup2() is different from that returned  by  fcntl(...,  F_DUPFD,  ...)   when newfd is out of range.  On some systems dup2() also sometimes returns EINVAL like F_DUPFD.

 

If  newfd  was open, any errors that would have been reported at close(2) time are lost.  A careful programmer will not use dup2() or dup3() without closing newfd first.

 

dup2函数的作用就是文件描述符重定向的作用。

例如下面的程序：将stdout重定向到一个指定的文件描述符中。

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

using namespace std;

int main()
{
        FILE *fp = NULL;
        int fd1;
        fprintf( stdout, "[%d]dup2 test\n", __LINE__ );

        fd1 = open( "dup2.txt", (O_RDWR), 0644 );
        if( fp < 0 )
        {
                printf( "[%d]fopen error=[%s]\n", __LINE__, strerror(errno) );
                return 1;
        }

        if( dup2( fd1, 1 ) < 0 )
        {
                printf( "[%d]dup2 error=[%s]\n", __LINE__, strerror(errno) );
        }
        close( fd1 );

        fprintf( stdout, "[%d]dup2 test\n", __LINE__ );
        fprintf( stdout, "[%d]dup2 test\n", __LINE__ );
}
~

也可参考如下文章。