SDL program returns 3, debugger gives Segmentation fault

Hello, I'm new to programming, and I'm trying to learn SDL using (mostly) LazyFoo's tutorials.

I'm using Code::Blocks in Windows XP, and when trying to run my program, it returns 3. The code is below, I think the problem is in the loadf() function, but I can't find it.

I tried to use the debugger, which gives me the message below:

Code:

---

Program received signal SIGSEGV, Segmentation fault. In ?? () ()

---

If I'm not mistaken, this message means that the program is referencing a rogue pointer, or generally a piece of memory it is not supposed to. But I check my code again and again, and I can't find where the problem is.

The files work perfectly in my previous simpler programs, and the load() and loadf() code is nearly identical.

I'm really not very experienced, since I only started learning programming about two months ago, and some help with this would really be appreciated.

Please excuse the length of the code. I post all of it here because I don't know what function the problem is in.

Thank you in advance.

Code:

---

#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include "SDL/SDL_ttf.h"
#include "SDL/SDL_mixer.h"
#include <string>

const int SW = 640;
const int SH = 480;
const int BPP = 32;

SDL_Surface * screen = NULL;
SDL_Surface * background = NULL;
SDL_Surface * faces = NULL;
SDL_Surface * text = NULL;

Mix_Chunk * up = NULL;
Mix_Chunk * down = NULL;
Mix_Chunk * left = NULL;
Mix_Chunk * right = NULL;

SDL_Rect clip[5];

SDL_Event event;

TTF_Font * font = NULL;
SDL_Color tcolor = { 255 , 255 , 255 };

bool init()
{
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;
    }

    screen = SDL_SetVideoMode( SW , SH , BPP , SDL_SWSURFACE );

    if( screen == NULL || TTF_Init() == -1 )
    {
        return false;
    }

    if( Mix_OpenAudio( 22050 , MIX_DEFAULT_FORMAT , 2 , 4096 ) == -1 )
    {
        return false;
    }

    SDL_WM_SetCaption( "Directions w/ sound!" , NULL );

    return true;
}

void clean()
{
    SDL_FreeSurface( background );
    SDL_FreeSurface( faces );
    SDL_FreeSurface( text );

    Mix_FreeChunk( up );
    Mix_FreeChunk( down );
    Mix_FreeChunk( left );
    Mix_FreeChunk( right );
    Mix_CloseAudio();

    TTF_CloseFont( font );
    TTF_Quit();

    SDL_Quit();
}

SDL_Surface * load( std::string file )
{
    SDL_Surface * loaded = NULL;
    SDL_Surface * optimized = NULL;

    loaded = IMG_Load( file.c_str() );

    if( loaded != NULL )
    {
        optimized = SDL_DisplayFormatAlpha( loaded );
        SDL_FreeSurface( loaded );
    }

    return optimized;
}

bool loadf()
{
    background = load( "bg.png" );
    faces = load( "d.png" );
    font = TTF_OpenFont( "Qarmic_sans_Abridged.ttf" , 24 );

    if( background == NULL )
    {
        return false;
    }

    if( faces == NULL )
    {
        return false;
    }

    if( font == NULL )
    {
        return false;
    }

    up = Mix_LoadWAV( "up.wav" );
    down = Mix_LoadWAV( "down.wav" );
    left = Mix_LoadWAV( "left.wav" );
    right = Mix_LoadWAV( "right.wav" );

    if( up == NULL || down == NULL || left == NULL || right == NULL )
    {
        return false;
    }

    return true;
}

void apply( int x , int y , SDL_Surface * get = NULL , SDL_Surface * give = NULL , SDL_Rect * clips = NULL )
{
    SDL_Rect off;

    off.x = x;
    off.y = y;

    SDL_BlitSurface( get , clips , give , &off );
}

void clipping()
{
    clip[0].x = 0;
    clip[0].y = 0;
    clip[0].w = 100;
    clip[0].h = 100;

    clip[1].x = 100;
    clip[1].y = 0;
    clip[1].w = 100;
    clip[1].h = 100;

    clip[2].x = 0;
    clip[2].y = 100;
    clip[2].w = 100;
    clip[2].h = 100;

    clip[3].x = 100;
    clip[3].y = 100;
    clip[3].w = 100;
    clip[3].h = 100;

    clip[4].x = 0;
    clip[4].y = 200;
    clip[4].w = 100;
    clip[4].h = 100;
}

int run( int num , std::string direct , int fw , int fh , int tw , int th )
{
    text = TTF_RenderText_Solid( font , direct.c_str() , tcolor );

    if( text != NULL )
    {
        apply( 0 , 0 , background , screen );
        apply( fw , fh , faces , screen , &clip[num] );
        apply( tw , th , text , screen );
    }

    if( SDL_Flip( screen ) == -1 )
    {
        return 1;
    }
}

int main( int argc , char * args[] )
{
    bool quit = false;

    if( init() == false )
    {
        return 2;
    }

    if( loadf() == false )
    {
        return 3;
    }

    if( clip != NULL )
    {
        clipping();
    }

    run( 0 , "Center!" , 290 , 180 , ( SW - text->w ) / 2 , 290 );

    while( quit == false )
    {
        while( SDL_PollEvent( &event ) )
        {
            if( event.type == SDL_QUIT )
            {
                quit = true;
            }
        }

        Uint8 * keys = SDL_GetKeyState( NULL );

        if( keys[SDLK_UP] )
        {
            run( 1 , "Up!" , 290 , 10 , ( SW - text->w ) / 2 , 120 );

            if( Mix_PlayChannel( -1 , up , 0 ) == -1 )
            {
                return 4;
            }
        }

        if( keys[SDLK_DOWN] )
        {
            run( 2 , "Down!" , 290 , 500 , ( SW - text->w ) / 2 , 600 );

            if( Mix_PlayChannel( -1 , down , 0 ) == -1 )
            {
                return 4;
            }
        }

        if( keys[SDLK_LEFT] )
        {
            run( 3 , "Left!" , 10 , 190 , 10 , 290 );

            if( Mix_PlayChannel( -1 , left , 0 ) == -1 )
            {
                return 4;
            }
        }

        if( keys[SDLK_RIGHT] )
        {
            run( 4 , "Right!" , 370 , 190 , 370 , 290 );

            if( Mix_PlayChannel( -1 , right , 0 ) )
            {
                return 4;
            }
        }

        if( keys[SDLK_SPACE] )
        {
            run( 0 , "Center!" , 290 , 180 , ( SW - text->w ) / 2 , 290 );
        }
    }

    clean();

    return 0;
}

---

Code:

---

Program received signal SIGSEGV, Segmentation fault.
0x000000000040161d in main (argc=1, args=0x7fffffffe278) at bar.cpp:194
194            run( 0 , "Center!" , 290 , 180 , ( SW - text->w ) / 2 , 290 );
(gdb) print SW
$1 = 640
(gdb) print text
$2 = (SDL_Surface *) 0x0
(gdb)

---

You don't set text until the function is called.

Thanks a ton! :D

I re-wrote the code correctly this time, and now it (sort of) works.
It has some problem playing the sounds, some times at the first keystroke, other times at the second, but I'll try to figure this one out by myself. :)

Again, thank you very much for the help! :)

Code:

---

#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include "SDL/SDL_ttf.h"
#include "SDL/SDL_mixer.h"
#include <string>

const int SW = 640;
const int SH = 480;
const int BPP = 32;

SDL_Surface * screen = NULL;
SDL_Surface * background = NULL;
SDL_Surface * faces = NULL;
SDL_Surface * text = NULL;

Mix_Chunk * up = NULL;
Mix_Chunk * down = NULL;
Mix_Chunk * left = NULL;
Mix_Chunk * right = NULL;

SDL_Rect clip[5];

SDL_Event event;

TTF_Font * font = NULL;
SDL_Color tcolor = { 255 , 255 , 255 };

bool init()
{
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;
    }

    screen = SDL_SetVideoMode( SW , SH , BPP , SDL_SWSURFACE );

    if( screen == NULL || TTF_Init() == -1 )
    {
        return false;
    }

    if( Mix_OpenAudio( 22050 , MIX_DEFAULT_FORMAT , 2 , 4096 ) == -1 )
    {
        return false;
    }

    SDL_WM_SetCaption( "Directions w/ sound!" , NULL );

    return true;
}

void clean()
{
    SDL_FreeSurface( background );
    SDL_FreeSurface( faces );
    SDL_FreeSurface( text );

    TTF_CloseFont( font );
    TTF_Quit();

    Mix_FreeChunk( up );
    Mix_FreeChunk( down );
    Mix_FreeChunk( left );
    Mix_FreeChunk( right );
    Mix_CloseAudio();

    SDL_Quit();
}

SDL_Surface * load( std::string file )
{
    SDL_Surface * loaded = NULL;
    SDL_Surface * optimized = NULL;

    loaded = IMG_Load( file.c_str() );

    if( loaded != NULL )
    {
        optimized = SDL_DisplayFormatAlpha( loaded );
        SDL_FreeSurface( loaded );
    }

    return optimized;
}

bool loadf()
{
    background = load( "bg.png" );
    faces = load( "d.png" );
    font = TTF_OpenFont( "Qarmic_sans_Abridged.ttf" , 24 );

    if( background == NULL )
    {
        return false;
    }

    if( faces == NULL )
    {
        return false;
    }

    if( font == NULL )
    {
        return false;
    }

    up = Mix_LoadWAV( "up.wav" );
    down = Mix_LoadWAV( "down.wav" );
    left = Mix_LoadWAV( "left.wav" );
    right = Mix_LoadWAV( "right.wav" );

    if( up == NULL || down == NULL || left == NULL || right == NULL )
    {
        return false;
    }

    return true;
}

void apply( int x , int y , SDL_Surface * get = NULL , SDL_Surface * give = NULL , SDL_Rect * clips = NULL )
{
    SDL_Rect off;

    off.x = x;
    off.y = y;

    SDL_BlitSurface( get , clips , give , &off );
}

void clipping()
{
    clip[0].x = 0;
    clip[0].y = 0;
    clip[0].w = 100;
    clip[0].h = 100;

    clip[1].x = 100;
    clip[1].y = 0;
    clip[1].w = 100;
    clip[1].h = 100;

    clip[2].x = 0;
    clip[2].y = 100;
    clip[2].w = 100;
    clip[2].h = 100;

    clip[3].x = 100;
    clip[3].y = 100;
    clip[3].w = 100;
    clip[3].h = 100;

    clip[4].x = 0;
    clip[4].y = 200;
    clip[4].w = 100;
    clip[4].h = 100;
}

void run( int n , std::string d , int fw , int fh )
{
    text = TTF_RenderText_Solid( font , d.c_str() , tcolor );

    if( text != NULL )
    {
        apply( 0 , 0 , background , screen );
        apply( fw , fh , faces , screen , &clip[n] );
        apply( fw , fh + 100 , text , screen );
    }

    SDL_Flip( screen );
}

int main( int argc , char * args[] )
{
    bool quit = false;

    if( init() == false )
    {
        return 2;
    }

    if( loadf() == false )
    {
        return 3;
    }

    if( clip != NULL )
    {
        clipping();
    }

    run( 0 , "Center!" , 290 , 180 );

    while( quit == false )
    {
        while( SDL_PollEvent( &event ) )
        {
            if( event.type == SDL_QUIT )
            {
                quit = true;
            }
        }

        Uint8 * keys = SDL_GetKeyState( NULL );

        if( keys[SDLK_UP] )
        {
            run( 1 , "Up!" , 290 , 10 );

            if( Mix_PlayChannel( -1 , up , 0 ) == -1 )
            {
                return 4;
            }
        }

        if( keys[SDLK_DOWN] )
        {
            run( 2 , "Down!" , 290 , 340 );

            if( Mix_PlayChannel( -1 , down , 0 ) == -1 )
            {
                return 5;
            }
        }

        if( keys[SDLK_LEFT] )
        {
            run( 3 , "Left!" , 10 , 180 );

            if( Mix_PlayChannel( -1 , left , 0 ) == -1 )
            {
                return 6;
            }
        }

        if( keys[SDLK_RIGHT] )
        {
            run( 4 , "Right!" , 530 , 180 );

            if( Mix_PlayChannel( -1 , right , 0 ) == -1 )
            {
                return 7;
            }
        }

        if( keys[SDLK_SPACE] )
        {
            run( 0 , "Center!" , 290 , 180 );
        }
    }

    clean();

    return 0;
}

---

Turns out I can't figure it out it after all.

Code:

---

if( Mix_PlayChannel( -1 , up , 0 ) == -1 ){

    return 1;

}

---

For some reason in the program on my previous post, Mix_PlayChannel() gives -1, so with the above code the program returns 1.

But if I remove the "if" segment, and write it like this...

Code:

---

Mix_PlayChannel( -1 , up , 0 );

---

...It works fine, even though some times it plays the sound twice.

It's just a minor complaint, but it would be nice to know what causes this.

Thank you in advance.

SDL_GetError - SDL Documentation Wiki
Does this tell you anything, if you call it after the function has returned -1

No, it gives nothing.
The program works fine though if I add "printf( SDL_GetError() );" INSTEAD of "return 1;".
Generally it works fine if I do not have it return anything if Mix_PlayChannel() gives -1.

Try moving all your Mix_PlayChannel's into one function that does NOTHING but take an input and play the given sound. And then replace it with just a line of text that prints what sound it thinks it should play. This will help eliminate things like you having to have time to hear the sound, playing "NULL" sounds, etc.

Compartmentalising your program like this is not only good programming practice but extremely helpful for debugging. I can't see anything at first sight but you call the functions multiple times inside an open loop that's likely to spin very fast so it's hard to tell what might go wrong.

Also, because of your loop, when it does work it's likely to loop so fast that it will play the sounds and fill every audio channel so long as you have the button down for more than a tiny fraction of a second. It will literally just keep playing the sound again and again while the button is down. Hell, from what I see you could be easily filling all audio channels with a single keypress and that's why Mix_PlayChannel fails. Either adjust your loop to "debounce" your input (i.e. only spot when the changes state, not look for if the key is currently pressed), or use SDL's proper keyboard events (you're already polling the event loop and could easily just check for the event being a key up/down event while you are there).

But, personally, I'd be pulling out all the PlayChannel's to find your problem and put them into a general purpose function that I would then debug the calling of (e.g. by temporarily replacing or supplementing the actual PlayChannel call inside it with a printf with some helpful information (e.g. the sound file played, the error from PlayChannel for that one, etc.).

I noticed your arguments to main are called argc and args, i've had issues with this before. Apparently SDL is picky about this, try renaming it to argv instead of args. I believe this mismatch results in a strange linker error so it's likely not the root of your issues, but worth a shot.

use your debug console to track keypresses and calls as suggested above

Thanks for the suggestions everybody.
When I find some time I'll try them all, and I'll let you know. :)
Thanks again. :)