Decide an application to be of console/windows subsystem at run time

Question

I have an MFC application that generates some reports and shows the same in the GUI. I have a requirement of running it as a console application, when passed with certain commandline argument. In the console mode it will generate the reports/errors in standard output/error and I should be able to redirect the same to any file.

For Ex. C:/temp MyApp.exe --console > report.txt should run my exe in console mode and redirect all the output to a text file. But if I run it without any console argument, it should be like a default MFC application.

To achieve my requirement, so far I have done is, changed the Linker > System > Subsytem from Windows to Console and added WinMainCRTStartup at Linker > Advanced > Entry Point

So now my app works fine when I run it with --console parameter from console/batch files. But when I run it directly, it still opens a cmd window (of course because it is now a console application). However, I am using FreeConsole() method to get rid of it but it still flashes for a brief second.

So I am just curious if there is a way to get rid of it completely, either by deciding the application's subsytem at run time or any other trick? Any suggestion will be appreciated.

Answer 1

I'd suggest to keep your GUI application with the windows subsystem.

At the very beginning, when parsing command line, instead of creating the GUI windows (MFC inistialisation), you could create a console or attach with AttachConsole()

As a proof of concept, here how it could look like (for example in CxxxApp::InitInstance()):

...  // init code but before the the CMainFrame is created 

if(...) {   // suppose you want to go to the console
    if (! AttachConsole(ATTACH_PARENT_PROCESS))   // try to hijack existing console of command line
        AllocConsole();                           // or create your own.

    DWORD nw,nr;    // demo with windows native console i/o 
    char buff[32]; 
    WriteConsole(GetStdHandle(STD_OUTPUT_HANDLE), L"Who are you ? ", 14, &nw, NULL); 
    ReadConsoleA(GetStdHandle(STD_INPUT_HANDLE), buff, sizeof(buff), &nr, NULL);
    WriteConsoleA(GetStdHandle(STD_OUTPUT_HANDLE), "Hello ", 6, &nw, NULL);
    WriteConsoleA(GetStdHandle(STD_OUTPUT_HANDLE), buff, nr, &nw, NULL);
    ReadConsoleA(GetStdHandle(STD_INPUT_HANDLE), buff, 1, &nr, NULL);
    ...
}

If you want to use C++ cin/cout, additional work is however needed. This other SO question addresses for example the redirecting of cout.