CODEWITHSUNDEEP
cwindowsvisual-c++
McBob
McBob

Reputation: 1011

Redirect STDOUT using _pipe non block

As the title says Im trying to redirect stdout, to test I have the following program:

#include <windows.h>
#include <stdio.h>
#include <io.h>
#include <fcntl.h>

#define BUFFER_SIZE 4096 

int main(int argc, char* argv[])
{
    int fdStdOutPipe[2];
    int fdStdOut;

    printf("Console Print...\n");

    // Start
    fflush(stdout);
    _pipe(fdStdOutPipe, BUFFER_SIZE, O_RAW);
    fdStdOut = _dup(_fileno(stdout));
    _dup2(fdStdOutPipe[1], _fileno(stdout));
    setvbuf( stdout, NULL, _IONBF, 0 );
    fdStdOut = _dup(_fileno(stdout));

    printf("Buffer Print...\n");

    char buffer[ BUFFER_SIZE ] = "";

    while( _read( fdStdOutPipe[0], buffer, BUFFER_SIZE ) )
    {
        // Test
        int l = strlen( buffer );
        buffer[ 0 ] = 0;
    }


    // Close
    _dup2(fdStdOut, _fileno(stdout));
    _close(fdStdOut);
    _close(fdStdOutPipe[0]);
    _close(fdStdOutPipe[1]);

    printf("Console Print Again...\n");

    return 0;
}

The issue that Im having is that after that _read is blocking if the stdout pipe is empty... I was under the impression that pipes are non block by default. Is there any way that I can make the pipe in the example above non block?

Upvotes: 2

Views: 489

Answers (1)

hacyaman
hacyaman

Reputation: 26

Before calling _read(), check the pipe status can solve the problem. I'm using this code on VC++ and works fine.

struct _stat st;
if(_fstat(fdStdOutPipe[0], &st)) {
    // do error handling
}
if (st.st_size) {
    // data is available to read
    while(_read(...)) {
    }
}

Upvotes: 1

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