Segmentation fault on library call

问题:

I'm using a physics library called Chipmunk for a game that I'm writing.

In my initialize function I initialize the global variable cpSpace space. Then in update I call cpSpaceStep(space, timestep). The prototype for this function is void cpSpaceStep(cpSpace *space, cpFloat dt);. I'm getting a segfault on this function call. I've marked those two function calls in the code below.

The full code is below:

#include "../include/SDL/SDL_image.h"
#include "../include/SDL/SDL.h"
#include "../include/Player.h"
#include "../include/Timer.h"
#include "../include/Block.h"
#include "../include/ImageLoader.h"
#include "../include/chipmunk/chipmunk.h"
#include <string>

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The frame rate
const int FRAMES_PER_SECOND = 60;

SDL_Event event;
SDL_Surface *screen = NULL;
SDL_Surface *player_img = NULL, *block_img = NULL;
Player *player;
Timer fps;
cpSpace *space;

bool quit = false;

void initialize();
void update();

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

    return 1;
}

void initialize()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {

    }

    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );

    //If there was an error in setting up the screen
    if( screen == NULL )
    {

    }

    //Set the window caption
    SDL_WM_SetCaption( "Move the Dot", NULL );

    cpVect gravity = cpv(0, 100);

//******************cpSpacenew()*****************       
//This is where space is init'ed
    space = cpSpaceNew();
//***********************************************


}

void update()
{
    //While the user hasn't quit
    while( quit == false )
    {
        //Start the frame timer
        fps.start();

        while( SDL_PollEvent( &event ) )
        {
            //Handle events for the dot
            player->handle_input( &event );

            //If the user has Xed out the window
            if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
        }

        player->update();

        cpFloat timeStep = 1.0/FRAMES_PER_SECOND; 

  //************************Segfault**********************************************
        cpSpaceStep(space, timeStep);
  //******************************************************************************

        //Cap the frame rate
        if( fps.get_ticks() < 1000 / FRAMES_PER_SECOND )
        {
            SDL_Delay( ( 1000 / FRAMES_PER_SECOND ) - fps.get_ticks() );
        }
    }
}

回答1:

Where's your cpInitChipmunk() call? Without that, it's likely that cpSpaceNew() may well return NULL (or junk).

Easy enough to check. Immediately after the call to cpSpaceNew(), insert a:

printf ("%p\n", space);

(or something equivalent, to see what the value is.

You may also want to do that immediatley before trying to use it as well, just in case something corrupts it.

回答2:

Could be because space is NULL when you call cpSpaceStep(). And in cpSpaceStep() function, an attempt is done to dereference the pointer which is NULL. Check whether space is properly initialized in initialize().