redirecting debug output to a file on Windows

[Lubomir I. Ivanov]

On 3 February 2017 at 01:04, Dirk Hohndel <dirk at hohndel.org> wrote:
> On Fri, Feb 03, 2017 at 12:46:51AM +0200, Lubomir I. Ivanov wrote:
>>
>> ok, so i've created a standalone test case and it appears that this
>> type of redirection never worked.
>>
>> that's because the application EXE is a GUI application (-mwindows)
>> and even if we redirect text to some console (via AttachConsole()), we
>> cannot redirect the output of the executable call to a file, like so:
>> gui_windows_test.exe > test.log
>>
>> because the GUI executable itself has no output, if that makes sense.
>
> I would have bet that it worked. But I looked through the email archive
> and couldn't find actual PROOF that it worked...
>
>> solutions:
>>
>> 1) my last patch...it writes separate log files for stderr / stdout
>> it can write the output to the same file with this (mod in
>> windows.c::subsurface_console_init()):
>>
>> const char *location = logfile ? "subsurface.log" : "CON";
>> console_desc.out = freopen(location, "w", stdout);
>> *stderr = *stdout; // seems safe
>> setvbuf(stderr, NULL, _IONBF, 0); // disable buffering
>> setvbuf(stdout, NULL, _IONBF, 0);
>
> I think having it write to two files is fine. I really see this as a very
> rarely used oddity if we really need someone to be able to capture debug
> output on Windows. This shouldn't be necessary and I don't want us to
> spend too much time on making it perfect.
>
> One question, though: is the other win32console option still needed?

yes, it is. but it's only viable for a GUI build (-mwindows) and if
the user starts the the EXE from a shortcut.
in such a case a console window will be created explicitly, so that
the user can look at stdout/stderr if she/he needs to.

--win32log on the other hand will create a console window (so performs
a win32console, not really needed), but leaves it empty and writes all
output to log files.

that's how it works ATM. it's not super refined, but it's for
debugging after all.

>
>> 2) create a windows console application
>> stderr / stdout redirection of a windows console application will work for sure.
>>
>> also define WIN32_CONSOLE_APP (-DWIN32_CONSOLE_APP)
>>
>> QMAKE had this:
>> CONFIG += console
>>
>> for CMAKE:
>> http://stackoverflow.com/questions/2753761/how-do-i-tell-cmake-not-to-create-a-console-window
>
> I guess I'm confused what the pros and cons are... i.e., we gain the
> ability to rediret stdout/stderr, what do we lose?
>

a console window is always created when the user starts the EXE which
is a -mconsole application (not a -mwindows GUI application).
so imagine a desktop shortcut on Windows - the users starts it, but
first a console windows pops up (as this EXE is a console app) and
only then the GUI appears.
if the user closes the console Window the GUI will close as well.

that can be classified as a downside, but depends on the POV.

lubomir
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