Question

I’ve got a Windows application (written in C, compiled with MSVC Express edition, 32-bit mode), which has two main modes of operation:

• Windowed mode — create a window, and draw stuff in it (namely, a fractal).
• Benchmark mode — when run with --benchmark as an argument, don’t make a window but just print some benchmark statistics to stdout.

During development I’ve compiled as a Console app, and used SDL to create the window and perform other GUI functions. So benchmark mode runs fine (no window is created), and graphical mode just has a lingering console window.

However for my release compilation I’ve enabled the Windows subsystem instead of Console. (As explained in this question). This works great except I’ve suddenly discovered I can’t run benchmarks any more. 😮

I’m just wondering, is there a way for an application to choose at run time (e.g. based on the command line it’s given) which kind of subsystem behaviour to use?

I’ve done some experimentation with EXE files in Windows (explorer, notepad, winword) and none of them seem to print anything to the console when run with an argument like “/?” (which most Windows console apps support). So it doesn’t look like it, but I thought it’s worth asking here in case there’s a special trick.

Update. It looks like, no, you can’t. Thanks for the answers guys.

Additional academic question. Does this mean that the subsystem choice is marked in the EXE header, and it’s the operating system that examines this and sets up the Window or connects it to the console it’s run from? I don’t know much about EXE loading, but I would be curious to learn a few details here.

Conclusion. I think there are four good solutions (plus two semi-solutions, making five total :p) to choose from:

1. Use the console subsystem, but use FreeConsole when running in GUI mode.
2. Use the windows system, and use AllocConsole when running in benchmark mode. Not perfect if fractal.exe is run from an existing console, so I’ll count this as half a solution ;-).
3. Just have one executable for each subsystem, fractal.exe and fractalgui.exe.
4. Have two (or more) executables, one of which does the work and passes it to the other to be displayed on the console or in a Window as appropriate. Needs some thought on how to divide the programs and how to communicate between them.
5. Another half-solution: have fractalgui.exe print the benchmark to standard out, and pipe that to a utility that will simply print it.

I haven’t yet chosen, but I’m leaning towards #3.

Thanks to Matteo and smerlin for the ideas!

Answer 1

There is no way a application can choose her subsystem at runtime (well there are some really ugly workarounds, but those are full of quirks).

Then general solution for this problem is to have a console application, which starts your gui application if necessary

For your benchmark case, it would just print your benchmark statistics.

example setup:
– fractalgui.exe (subsystem: windows)
– fractal.exe (subsystem: console)

* the shortcut on the user desktop links to your fractalgui.exe
* if the user starts fractal.exe from the console, fractal exe starts fractalgui.exe
* if the user starts fractal.exe --benchmark, it either does the benchmark itself (if its possible to add this benchmark logic to another executable) and prints the information directly to console, or – if thats not possible – it will need to start fractalgui.exe --nogui --benchmark. The tricky case here is to get your output from fractalgui.exe to fractal.exe, so you can print it on the appropriate console. There are several ways to do this, e.g. named pipes (there are ways to start fractalgui.exe in a way, that you can just use stdout / cout there, and the data will be piped to the stdout of fractal.exe, but i dont recall how excactly this works anymore (edit: maybe this works)). The easiest way would be to start fractalgui.exe --nogui --benchmark > mylogfile and then print mylogfile after fractalgui.exe finished (since stdout/cout of fractalgui.exe will work if the output is redirected to a file), however you wont get “live” output, since all the output will be printed on the console when fractalgui.exe is already finished.