Wednesday, August 6, 2008

Redirect Standard Out, The old (C) style

We have a third party library that outputs some debug/trace information when executes, this is of course not very nice when you have a command line application that calls the library.

The solution we used is to have a wrapper around the library, which redirects stdout before the call and restores it after.

An initial attempt to do this with Windows APIs (GetStdHandle/SetStdHandle) was unsuccessful probably because C runtime keeps its own handles. So, we had to go down and dirty to the low level C APIs (and this works fine):

    //keep a handle and close stdout
    int handle = _dup(1);

    // call the lib function here

    //restore stdout, close the copy
    _dup2(handle, 1);