windows - Why does WriteFile crash when writing to the standard output?

Question

Here's a "Hello world" program that uses WinAPI's WriteFile (compiled in Microsoft Visual C++ 2008 Express):

int _tmain(int argc, _TCHAR* argv[])
{
    wchar_t str[] = L"Hello world";

    HANDLE out = GetStdHandle(STD_OUTPUT_HANDLE);
    if(out && out!=INVALID_HANDLE_VALUE)
    {
        WriteFile(out, str, sizeof(str), NULL, NULL);
        CloseHandle(out);
    }   

    return 0;
}

If executed in a console window, it happily greets the world. If you try to redirect its standard output, however, as in

hello.exe > output.txt

the program crashes in WriteFile (NULL pointer exception). Nonetheless, output.txt exists and contains the correct output in its entirety.

The call stack on crash:

KernelBase.dll!_WriteFile@20()  + 0x75 bytes    
kernel32.dll!_WriteFileImplementation@20()  + 0x4e bytes    
srgprc2.exe!wmain(int argc=1, wchar_t * * argv=0x00483d88)  Line 15 + 0x16 bytes    C++

The message: "Unhandled exception at 0x75ce85ea (KernelBase.dll) in srgprc2.exe: 0xC0000005: Access violation writing location 0x00000000."

What's going on here? Thanks!

Answer 1

The fourth parameter to WriteFile is not optional. You are passing NULL, which is not allowed.