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SDL - Error in Visual Studio 2010 Express when Debugging

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Hey everyone,

 

I'm going through lazy foo's SDL tutorials using Visual C++  2010 Express and have noticed that everything in the first basic tutorial works fine when I run the application directly from the .exe, but when I try to click "play" to start debugging, I get the following error:

 

Unhandled exception at 0x681247d8 in test_game.exe: 0xC0000005: Access violation reading location 0xccccccf8.

 

I'm guessing this is due to one of two things:

1) The debug environment isn't finding the necessary DLLs

2) The debug environment isn't finding the necessary images to load, so it's trying to dereference a null pointer.

 

Unfortunately, I know next to nothing about Visual Studio or how it sets up its debug environment and I haven't been able to google a solution to this.  Any thoughts?

 

Thanks in advance, please let me know if I should provide more detail.

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Use the debugger to find the line in your code that this occurs.  If you can't figure it out post a test case on ideone.com .

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It breaks on the following line:

 

SDL_BlitSurface( source, NULL, destination, &offset );

 

If you'd like to see this in context....

 

 

#include "SDL.h"
#include "SDL_image.h"
#include <string>
 
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;
 
SDL_Surface *message = NULL;
SDL_Surface *background = NULL;
SDL_Surface *screen = NULL;
 
SDL_Surface *load_image( std::string filename )
{
    // Temporary storage for the image that's loaded
    SDL_Surface* loadedImage = NULL;
 
    // The optimized image that will be used
    SDL_Surface* optimizedImage = NULL;
 
    // Load the image
    loadedImage = SDL_LoadBMP( filename.c_str() );
 
    if (loadedImage != NULL)
    {
        // Create an optimized image
        optimizedImage = SDL_DisplayFormat( loadedImage );
 
        // Free the old image
        SDL_FreeSurface( loadedImage );
 
        return optimizedImage;
    }
}
 
void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination )
{
    // Make a temporary rectangle to hold the offsets and assign their values
    SDL_Rect offset;
    offset.x = x;
    offset.y = y;
 
    // Blit the surface
    SDL_BlitSurface( source, NULL, destination, &offset );
}
 
int main(int arg, char** argv)
{
    if ( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return 1;
    }
 
    // Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
    if ( screen == NULL )
    {
        return 1;
    }
 
    // Set the window caption
    SDL_WM_SetCaption( "Hello World", NULL );
 
    // Load the images
    message = load_image( "hello.bmp" );
    background = load_image( "background.bmp" );
 
    apply_surface( 0, 0, background, screen );
    apply_surface( 320, 0, background, screen );
    apply_surface( 0, 240, background, screen );
    apply_surface( 320, 240, background, screen );
 
    apply_surface( 180, 140, message, screen );
 
 
    // Update the screen
    if ( SDL_Flip( screen ) == -1 )
    {
        return 1;
    }
 
    // Wait 2 seconds
    SDL_Delay( 2000 );
 
    SDL_FreeSurface( message );
    SDL_FreeSurface( background );
 
    SDL_Quit();
 
    return 0;
}

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0xCCCCCCCC is MSVC's debug fill pattern for uninitialized memory. If you get an access violation in that neighborhood you probably haven't initialized everything properly. The first thing I would do is add code to check SDL_GetLastError() when your image loading fails.

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Thanks for the reply.  In light of what you said, my strong assumption here would be that it's not finding the image files in the debug environment.  When using visual studio, if I want to load a file does it have to go in a different directory when debugging (as opposed to in production)?

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Yes. With your current code, it'll search for the files in the folder that contains the executable. By default under VS these folders are called 'Release' and 'Debug'.

 

Add a check for NULL to your load_image calls and put your assets in some central location for the time being to save yourself from the headache of having to copy them over manually to the two folders each time you update them.

Edited by Indifferent

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In your project properties go to "Debugging" under "Configuration Properties"

 

Then Change the Working Directory to "..\Debug"

 

Depending on your setup it might be something else, but I had the same issue and that's what fixed it. Let me know if this works.

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In your project properties go to "Debugging" under "Configuration Properties"

 

Then Change the Working Directory to "..\Debug"

 

Depending on your setup it might be something else, but I had the same issue and that's what fixed it. Let me know if this works.

 

This did the trick.  You are a gentleman and a scholar, thanks!

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Glad to hear it worked, as I mentioned I had the same problem with the same tutorials and was pulling my hair out trying to get them to work. 

All the best!

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