Question

I’ve recently encountered the following problem with my application: it didn’t show any console output, though the console had been allocated by using AllocConsole. I managed to figure out soon that it was caused by an attempt (hidden deeply in code) to write to the console before the AllocConsole was called. So it looked like this:

Console.WriteLine("Foo"); // no console allocated yet
AllocConsole();           // console window appears
Console.WriteLine("Bar"); // expecting "Bar" in the console, but the console is blank

So my question is: why does this happen? I don’t see any exceptions (though I suppose they are there).

Answer 1

The first time you use Console.WriteLine, the Console class creates a TextWriter and associates it with the Console.Out property. The way it does this is to use Win32 to open the low-level file handle associated with the standard output file handle. If the standard output handle is invalid, Console.Out is set to TextWriter.Null, which discards all output.

The Win32 AllocConsole function, creates and sets the standard output handle so after calling it the standard output handle is either different or now valid. In either case, Console.Out has already been set either to use the old standard output or to discard all output.

To force a re-open of Console.Out after calling AllocConsole, you can use this method:

• Console.OpenStandardOutput