redirecting debug output to a file on Windows

[Lubomir I. Ivanov]

On 2 February 2017 at 21:56, Dirk Hohndel <dirk at hohndel.org> wrote:
> On Thu, Feb 02, 2017 at 09:51:47PM +0200, Lubomir I. Ivanov wrote:
>>
>> attached is updated patch to write separate output files:
>> subsurface_err.log
>> subsurface_out.log
>
> Good enough for the use case.
>
>> the real, clean solution, of course is to redirect from the CMD line,
>> but i have no idea why it no longer works.
>> i'm pretty sure that i've tried that and it worked when i wrote the
>> custom console code for windows.
>
> As I said, I am quite certain that this used to work.
> I love it when things stop working and no one knows why.
>

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.

*nix has that, but Windows doesn't.

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);

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

lubomir
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