// make a temp file to store the function's stdout
int newStdOut = mkstemp( "/tmp/stdout.XXXXXXX" );
// save the original stdout
int tmpStdOut = dup( STDOUT_FILENO );
// clear stdout
fflush( stdout );
// now point the stdout file descriptor to the file
dup2( newStdOut, STDOUT_FILENO );
// call the function we want to collect the stdout from
some_function();
// make sure stdout is empty
fflush( stdout );
// restore original stdout
dup2( tmpStdOut, STDOUT_FILENO );
// the tmp file now contains whatever some_function() wrote to stdout