Unix上的C ++：重定向Shell输出

Question

I have a command that compiles test.cpp and is supposed to store output in the output file. Here is an example of my generated cmd:

g++ tmp/test.cpp -o tmp/test &> tmp/compile.out

when I use system() , it does not work. Even though it creates output file, it still prints everything to the main console window. When I execute it in terminal, it works just fine.

I also tried use popen() and fgets() (just copying the code from here ) but same happened. I probably could just fork my process and use freopen or something but I have sockets and multiple threads running in the background. I guess they would be duplicated as well, which is not good.

Any ideas why it may fail?

Answer 1

According to the man-page of system , it invokes sh which is the standard bourne shell (not bash, Bourne Again SHell). And the bourne shell doesn't understand &> . So you might need to use the old style:

g++ tmp/test.cpp -o tmp/test >tmp/compile.out 2>&1

Answer 2

I tried the following variant on popen() and it worked for me under Mac OS X 10.7.2, gcc 4.2.1:

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>

int main (int argc, char **argv)
{
    FILE *fpipe;
    char *cmd = "foo &> bar";

    if ( !(fpipe = (FILE*)popen(cmd,"r")) ) {
        perror("Problems with pipe");
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

Compiling:

gcc -Wall test.c -o test

The binary test creates a file called bar , which contains the following output:

sh: foo: command not found

Which is what I would see if I typed foo &> bar at the shell.