SetStdHandle has no effect on cout/printf

Question

The title says it all. When I run the following code:

HANDLE hOut = GetStdHandle(STD_OUTPUT_HANDLE);
HANDLE hFile = CreateFile(TEXT(\"Foo.txt\"), GENERIC_WRI         


        

Answer 1

Here's a solution I put together (far from perfect of course). It calls a custom function for every character written to STDOUT. In my example, it forwards the stream to OutputDebugString calls.

#include 
#include 
#include 
#include 

#define STDOUT_FILENO 1
#define STDERR_FILENO 2

enum StdHandleToRedirect {
    STDOUT, STDERR
};

class StdRedirect {
public:
    /// Assumes the specified handle is still assigned to the default FILENO (STDOUT_FILENO/STDERR_FILENO)
    /// TODO allow redirection in every case
    /// callback will run in a new thread and will be notified of any character input to
    /// the specified std handle
    StdRedirect(StdHandleToRedirect h, std::function callback) : callback(callback) {
        CreatePipe(&readablePipeEnd, &writablePipeEnd, 0, 0);
        SetStdHandle(h == STDOUT ? STD_OUTPUT_HANDLE : STD_ERROR_HANDLE, writablePipeEnd);

        // Redirect (TODO: ERROR CHECKING)
        int writablePipeEndFileStream = _open_osfhandle((long)writablePipeEnd, 0);
        FILE* writablePipeEndFile = NULL;
        writablePipeEndFile = _fdopen(writablePipeEndFileStream, "wt");
        _dup2(_fileno(writablePipeEndFile), h == STDOUT ? STDOUT_FILENO : STDERR_FILENO);

        CreateThread(0, 0, (LPTHREAD_START_ROUTINE)stdreader, this, 0, 0);
    }

    // TODO implement destructor, cleanup, reset

private:
    // DWORD (WINAPI *PTHREAD_START_ROUTINE)(LPVOID lpThreadParameter)
    static void WINAPI stdreader(StdRedirect* redirector) {
        while (1) {
            char c;
            DWORD read;
            ::fflush(NULL); // force current stdout to become readable
            // TODO add error handling
            ReadFile(redirector->readablePipeEnd, (void*)&c, 1, &read, 0); // this blocks until input is available
            if (read == 1)
                redirector->callback(c);
        }
    }

    HANDLE readablePipeEnd, writablePipeEnd;
    const std::function callback;
};

int main() {
    std::function toOutputDebugString = [](char x) {
        char str[2] = {x, 0};
        OutputDebugStringA(str);
    };

    StdRedirect so(STDOUT, toOutputDebugString);
    std::cout << "test stdout\n";
    while (1); // busy loop to give the thread time to read stdout. 
    // You might want to look at "Output: Show output from: Debug" now.
    return 0;
}