Printf inside constructor not showing in console

Question

I have something weird happening where printf commands (inside a class constructor) are not being output to the console window.

Do you know why this would happen?

Some relevant information:

My project is a Native Win32 Windowed Application(not a Win32 Console Project)
I open the console window using AllocConsole() & _open_osfhandle().
The constructor that I call the printf commands from is part of a Singleton class and inside the private constructor I call a static function isTVManagerTaskScheduled().
If I use printf outside of the constructor then it works correctly, ie, data is printed to the console window.
The console window is used just for debugging my Win32 Application.
I am using C++ Visual Studio 2010 Express
If I dont call the static function isTVManagerTaskScheduled() from within the constructor then the printf's work correctly.

Do you know why this would happen?

My code:

// Public Static Class Variables //
const tstring TVManager::TASK_NAME          = _T("TV Manager");
const tstring TVManager::TASK_TIME_STAMP    = _T("2012-03-22T13:46:00");

// Private constructor
TVManager::TVManager(HWND hwnd)
{
    mainHwnd = hwnd;

    bool res = isTVManagerTaskScheduled();
    std::cout << "Res: " << res << endl; // does not print to console
    _tprintf(_T("RES: %d\n"), res);      // does not print to console

    if (!res) {
        _tprintf(_T("hit\n"));
        EasyTaskScheduler::ScheduleTaskAtLogon(TASK_NAME, CPP_Utilities::getProcessPath(), TASK_TIME_STAMP);
    }
}

// Public Static function //
bool TVManager::isTVManagerTaskScheduled()
{
    std::vector <tstring> curTasks = EasyTaskScheduler::RetrieveScheduledTasks();
    tstring defTaskName            = CPP_Utilities::toLower( TASK_NAME );

    for (int i=0; i<=curTasks.size(); i++) {
        tstring task = CPP_Utilities::toLower(curTasks.at(i));
        // The following printf doesn't get printed to console
        _tprintf(_T("size %d, Task %d: %s\n"), curTasks.size(), i, task.c_str());
        if (task.find( defTaskName ) != npos) {
            _tprintf(_T("returning true\n"));
            return true;
        }
    }

    _tprintf(_T("returning false\n"));
    return false;
}

// Public static function
TVManager* TVManager::getInstance(HWND hwnd)
{
    static TVManager instance(hwnd);
    return &instance;
}

// Usage: Inside main window proceedure
case WM_CREATE:
{
    CPP_Utilities::openConsoleWindow();
    tvManager = TVManager::getInstance(hwnd);
}
break;

maybe your object is constructed before the console is there? It's hard to say since you didn't really give us a working example. — Guy Sirton
@GuySirton Please see edits for how the class is used. But I am sure that the console exists prior to calling the constructor because other things are written to the console by that point. — sazr
@ChrisDesjardins do you mean just manually write lines to a text file or use a Visual Studio logfile(if they exist?) — sazr
Can you pare down the example code to a self-contained repro example? — Michael Burr

sazr sazr · Accepted Answer · 2013-03-30T10:56:28

The problem was I was accessing an invalid vector element here:

for (int i=0; i<=curTasks.size(); i++) {
   tstring task = CPP_Utilities::toLower(curTasks.at(i));

It should be:

for (int i=0; i<curTasks.size(); i++) {

The weird thing is that it never threw a runtime error or crashed. It just continue working except it didn't output anything to the console.

Printf inside constructor not showing in console

2 Answers