[SOLVED] C++/SDL segfault when using SDL_Flip()

coralfang · 04-12-2011, 06:12 PM

Hello, i have recently decided to start learning some c++ as with previous languages, i feel its easier to understand "how things work" by creating small games or animations.

I have come across this tutorial on SDL here:
http://cone3d.gamedev.net/cgi-bin/in...ls/gfxsdl/tut2

And here is the code i have put together after following that:
http://pastebin.com/JxjnaiM6 (for the sake of syntax highlighting

)

And compiled with:

Code:

g++ main.cpp -o main `sdl-config --libs --cflags`

Now for the issue, i can't seem to fix this error:

Code:

% ./main                                           
SDL Drawing Test!
zsh: segmentation fault  ./main

When i run it under gdb, the output shows:

Code:

% gdb main 
GNU gdb (GDB) 7.2
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/ricky/Devel/cpp-sdl/main...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/ricky/Devel/cpp-sdl/main 
[Thread debugging using libthread_db enabled]
SDL drawing test started!
[New Thread 0x7fffee678700 (LWP 23754)]
[Thread 0x7fffee678700 (LWP 23754) exited]

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b719f8 in SDL_Flip () from /usr/lib/libSDL-1.2.so.0
(gdb)

The only place i have SDL_Flip() mentioned is inside DrawScene(), i tried commenting out that line, obviously the application only then shows a black screen.

Any help explaining why this is segfaulting would be awesome, thanks.

coralfang · 04-12-2011, 06:16 PM

Oh wow i found out i redeclared:

Code:

SDL_Surface *screen;

in main()

Removed it and now it works!

Solved i guess.

tuxdev · 04-12-2011, 06:41 PM

GCC can warn you whenever you "shadow" a variable like this I forget the exact keyword, but it's included with -Wall -Werror options I always compile with (it's got plenty of other bug-catching goodies too).

coralfang · 04-12-2011, 06:59 PM

I think i'll be using that all the time from now on:

Code:

% g++ main.cpp -o main `sdl-config --libs --cflags` -Wshadow
main.cpp: In function ‘int main(int, char**)’:
main.cpp:109:15: warning: declaration of ‘screen’ shadows a global declaration
main.cpp:29:14: warning: shadowed declaration is here

Very Helpful, Cheers.