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cout with SDL

Started by Mr_Threepwood Jan 2, 2008 at 8:18 PM 14 replies 11.2k views

Original Post

Jan 2, 2008 at 8:18 PM

Ok this is a stupid error that seems fine to me but for some reason isn't working. Here's my code:


#include "SDL/SDL.h"

#include <cstdlib>
#include <iostream>

int main(int argc, char *argv[])
{

    std::cout << "Program starting";

    system ("PAUSE");

    return 0;
}

The thing that is really vexing me is that the above code doesn't print to the console, but if I comment out the SDL header it does. I need to be able to print stuff to the console while I'm using SDL so that I can debug parts the program that I'm making (connect 4). Does anyone know why this would be happening?

Ezbez

Jan 2, 2008 at 8:37 PM

Two reasons:
- With SDL the console is disabled. SDL uses windows, not consoles
- SDL redirects the standard output (both cout and printf()) to a file named... oh I can't remember now but it's like stdout.txt or something like that. It should be in the .exe's directory. You can, of course, change this using the standard library.

And finally, learn to use a good debugger. Printing values out is nice and all, but it pales in comparison to breakpoints, stepping through code, call stacks, and all the goodies that come with a debugger. Investing the time to learn how to use a debugger is truly well worth it.

Feralrath

Jan 2, 2008 at 9:10 PM

if you really want to use the console to display information about your program as its running you can look at AllocConsole and its functions to create a console window and write text to it.

Megaman_22

Jan 2, 2008 at 10:54 PM

If you're using Visual Studio, you can go into the project properties and change one of the settings so that a console window does pop up. It's Linker -> System -> SubsSystem, and you make sure it's set to "Console (/SUBSYSTEM:CONSOLE)"

Feralrath

Jan 3, 2008 at 2:12 AM

sdl overloads the << operator so that it writes to a file not the console window so that doesn't work.

Kylotan

Jan 3, 2008 at 4:13 AM

It doesn't actually overload the << operator, it just redirects the standard output to a file.

Ezbez

Jan 4, 2008 at 2:37 PM

I didn't think that SDL compiled with the subsystem set to CONSOLE. Anyone care to confirm/deny that? I'm pretty sure it has to be windows.

SiCrane

Jan 4, 2008 at 2:47 PM

Yes, it can.

Trenki

Jan 4, 2008 at 3:03 PM

The prefered way to include the SDL headers is by #include "SDL.h".

In MSVC you can simply set the subsystem in the linker settings to CONSOLE and you get a console window where cout will output.

If you are using MinGW/GCC you can simply write #undef main before the main function and SDLs init code which redirects output to a file won't be called.
This way cout also writes to the console. Doing this does not cause any problems afaik.

superpig

Jan 4, 2008 at 7:13 PM

Quote:
Original post by Ezbez
And finally, learn to use a good debugger. Printing values out is nice and all, but it pales in comparison to breakpoints, stepping through code, call stacks, and all the goodies that come with a debugger. Investing the time to learn how to use a debugger is truly well worth it.

Seconded.

Ezbez

Jan 4, 2008 at 7:20 PM

Quote:
Original post by SiCrane
Yes, it can.

Okay, but then I wonder why I was getting compiling errors just recently when I was using SDL with the CONSOLE subsytem. Perhaps it was another library I was using. Either way, good to know.

SiCrane

Jan 5, 2008 at 8:36 AM

Given that /subsystem:console is a linker setting and not a compiler setting, then why you would have compiler problems is completely beyond me.

rip-off

Jan 5, 2008 at 8:54 AM

You'll have to post your errors. My guess is that you aren't using SDL_main.lib properly. To make SDL reasonably source compatible across different platforms with different entry points (like WinMain()) SDL provides SDL_main.lib. This library contains (on windows) an implementation of WinMain(), which calls your main() (which is actually re#defined to be SDL_main(), which is why it must take exactly 2 arguments and why you must explicitly return a value from it).

If you choose not to use SDL_main.lib's functions, you have to replicate some of the functionality it represents. Looking at the source will give you an idea of how to do this (and why its generally not done ;).

I believe there is a flag you can pass when compiling the SDL library that disables redirection (I *think* it might be no-stdio-redirect). But that is generally not a good idea (you'll have to download development versions of SDL's dependencies).

On the other hand, if you just want to resurrect console output, do this:

// outside any function#ifdef _WIN32#define WIN32_LEAN_AND_MEAN#include <windows.h>#endif// inside main or an initialisation function, after calling SDL_Init (to be safe):#ifdef _WIN32	    const char * confile = "CONOUT$";        FreeConsole();    if(  !AllocConsole() )    {        // handle error somehow.    }    else    {       freopen(confile, "w", stdout);       freopen(confile, "w", stderr);    }#endif

Works For Me ^TM [smile]

Ezbez

Jan 5, 2008 at 9:02 AM

Quote:
Original post by SiCrane
Given that /subsystem:console is a linker setting and not a compiler setting, then why you would have compiler problems is completely beyond me.

Sorry, I meant compile-time errors by that. They really were linker errors. And now my program is compiling (err, linking) fine with a console subsystem. Oh well.

SiCrane

Jan 5, 2008 at 9:13 AM

Linker errors are still not compiler time errors. They're link time errors. All compiles take place before linking begins; compiling and linking are two separate stages of putting a program together.

Ezbez

Jan 6, 2008 at 4:11 AM

Okay, thanks for the correction.

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