How this code fragment in print.cpp ever works?

[leha-bot]

The current file location:

STL/stl/src/print.cpp

Line 43 in 48db51b

const bool _Is_unicode_console = GetConsoleMode(_Console_handle, &_Console_mode) != 0;

- claims that return value of GetConsoleMode() says that console is Unicode. But that's not true, or I didn't understand something? Sorry for (possibly) stupid question

[jovibor]

You can check the comment above this call, it says:

// We can check if _Console_handle actually refers to a console or not by checking the
// return value of GetConsoleMode().

If GetConsoleMode succeeds (returns non-zero), it means that the _Console_handle is a true console handle.
Maybe the name _Is_unicode_console is just a bit misleading.

[McPherran]

The answer by @jovibor is on the right track. Further elaboration:

const bool _Is_unicode_console = GetConsoleMode(_Console_handle, &_Console_mode) != 0;

The value that indicates Unicode mode is the value returned in "_Console_mode". "_Is_unicode_console" is not an accurate name and that's not the variable that indicates Unicode mode or not. "_Is_unicode_console" is a pass/fail status value that has nothing to do with the console mode (e.g. Unicode).

See this example:
const bool status = GetConsoleMode(_Console_handle, &_Console_mode) != 0;

Then, if status is true (OK), the actual value of interest is _Console_mode.

[StephanTLavavej]

But we don't inspect _Console_mode, so I'm missing something.

[jovibor]

But we don't inspect _Console_mode

But why should we?...
Here, only the return value of the GetConsoleMode method matters. Most of the confusion arises because of poor naming.
A more appropriate approach would be:

DWORD _Unused;
const bool _Is_Console_handle_a_valid_console = GetConsoleMode(_Console_handle, &_Unused) != 0;

It's a good candidate for a good first issue PR.

[StephanTLavavej]

I see, after looking into doing this rename, I think I understand the original rationale.

The _Console_mode could be renamed to _Unused_mode for a bit more clarity. However, _Is_unicode_console is consistent with naming/comments everywhere else. The part that I was confused about, is that "is Unicode console" seems to imply that we're worried about dealing with non-Unicode consoles. But there are no such things. Every console is Unicode like every kitty is cute. We're just trying to distinguish Unicode consoles from non-Unicode non-consoles (redirected to files, I believe).

I might rename the mode later but we should keep the bool as-is for consistency with the rest of the codebase.