Dup/dup2 Output redirect

Function Prototypes:
#include
int dup (int oldfd);
int dup2 (int oldfd,int newfd);
The DUP is used to replicate the file descriptors referred to by OLDFD. However, when replication succeeds, the smallest file descriptor that has not been used is returned. Returns 1 if there is an error, and the error code is stored in errno. The new file descriptor and parameters returned OLDFD point to the same file, share all the locks, read and write pointers, and various permissions or flags. .h>

1. Open a new file .h>

2. Turn off the standard output file symbol .h>

3. Call the DUP to the file descriptor .h>

4. When the file descriptor changes to 1.h>

5. Redirect the data you want to print to a file. .h>

#include <stdio.h>                                                                           #include <stdlib.h> #include <errno.h> #include <string.h> #include <unistd.h># include<fcntl.h> #include <sys/stat.h> #define  _PATH_FILE_   "./log" Int main () {     umask (0);     int fd=open (_path_file_,o_creat| o_rdwr,0644)     if (fd<0) {        perror ("open" );        return 1;    }     close (1);     int&Nbsp;new_fd=dup (FD);     close (FD);    int count=0;     while (count++<100)     {         printf ("helo world\n");     }    fflush (stdout);//must, printf redirected to full buffer, buffer full before flushing, resulting in file     close (NEW_FD) not written;     return 0;}

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Dup/dup2 Output redirect