程序收到信号SIGSEGV，分段故障。 在al_draw_tinted_bitmap中（位图= 0x0，色调= ...，dx = 0，dy = 0，标志= 0）

Question

I have a problem when trying to compile this game. I am using the Allegro 5 library in order to program a PacMan Videogame. The problem occurs in the runtime, it only opens the executable file and get closed inmediately. When I use the debugger of gcc the error that I get is the next one:

"Thread 1 "a.out" received signal SIGSEGV, Segmentation fault.
0x00007ffff79362af in al_draw_tinted_bitmap (bitmap=0x0, tint=..., dx=0, dy=0, 
    flags=0) at /home/pakoxtror/allegro-5.0/src/bitmap.c:316
aviso: El archivo fuente es más reciente que el ejecutable.
316    al_draw_tinted_bitmap_region(bitmap, tint, 0, 0,"

I was searching at some forums where they stated that the problem was that the bitmap was not set to null. I tried to correct it but still nothing is happening. Here is the code:

#include <allegro5/allegro.h>
#include <allegro5/allegro_font.h>
#include <allegro5/allegro_ttf.h>
#include <allegro5/allegro_native_dialog.h>
#include <cstdlib>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <allegro5/allegro_image.h>

#define MAXFILAS 20 //eje y
#define MAXCOLS 31 // eje x
#define ScreenWidth 800
#define ScreenHeight 600

ALLEGRO_DISPLAY *display;
ALLEGRO_EVENT_QUEUE *event_queue;
ALLEGRO_BITMAP *buffer = NULL;
ALLEGRO_BITMAP *roca= NULL;  //son variables
ALLEGRO_BITMAP *comida= NULL;
ALLEGRO_BITMAP *pacbmp= NULL;//declarar una variable para la imagen
ALLEGRO_BITMAP *pacman= NULL;////declarar una variable para la imagen pero más pequeño
ALLEGRO_BITMAP *muerte= NULL;


int dir = 4;
int px = 30 * 14, py = 30 * 17;
int anteriorpx, anteriorpy;

char mapa[MAXFILAS][MAXCOLS] = {
    "XXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
    "X o o|o o o XXXXX o o o| o oX",
    "X XXX XXXXX XXXXX XXXXX XXX X",
    "X XXX XXXXX XXXXX XXXXX XXX X",
    "X      o|o o o o o o|o      X",
    "XoXXXoXX XXXXXXXXXXX XXoXXXoX",
    "X    |XX     XXX     XX     X",
    "X XXXoXXXXXX XXX XXXXXX XXX X",
    "X XXXoXX ooo|ooo|ooo XXoXXX X",
    " o   |XX XXXXXXXXXXX XX|   o ",
    "X XXXoXX XXXXXXXXXXX XXoXXX X",
    "XoXXXoXX oo  ooo ooo XXoXXXoX",
    "X XXXoXXXXXX XXX XXXXXXoXXX X",
    "Xo    XX     XXX     XX    oX",
    "X XXXoXX XXXXXXXXXXX XXoXXX X",
    "XoXXX| o| o o o o o |o |XXXoX",
    "X XXXoXXXX XXXXXXXX XXX XXX X",
    "XoXXXoXXXX          XXX XXXoX",
    "X  o |o o  XXXXXXXX o o| o  X",
    "XXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
};

void dibujarmapa() {
    int row, col;
    for (row = 0; row < MAXFILAS; row++)
    {
        for (col = 0; col < MAXCOLS; col++)
        {
            if (mapa[row][col] == 'X')
            {
                al_draw_bitmap(roca, col * 30, row * 30, 0);
            }
            else if (mapa[row][col] == 'o')
            {
                al_draw_bitmap(comida, col * 30, row * 30, 0);
                if (py / 30 == row && px / 30 == col)
                {
                    mapa[row][col] = ' ';
                }
            }
        }
    }
}

void pantalla()
{

    al_draw_bitmap(buffer, 0, 800, 600);
}

void dibujarpersonaje() {
    al_draw_bitmap_region(pacman, dir * 33, 0, 0, 0, 33, 33, 0);//coordenadas para donde vamos a tomar la imagen del jugador en este caso dir*33 y 0 despues dos coordenadas donde vamos a pegar la imagen 0,0 y por ultimo las dimensiones de la imagen en este caso 33, 33
    al_draw_bitmap(pacman, px, py, 0);//para que el cuadro pacman tenga transparencia, creo que no es necesario en nuestro juego
}

bool gameover() {
    int row, col;
    for (row = 0; row < MAXFILAS; row++) {
        for (col = 0; col < MAXCOLS; col++) {
            if (mapa[row][col] == 'o') {
                return true;
            }
        }
    }
    return false;
};

class fantasma {
    ALLEGRO_BITMAP  *enemigobmp;
    ALLEGRO_BITMAP  *enemigo;
    int fdir;
    int _x, _y;

public:
    fantasma(int x, int y); //constructor
    void dibujarfantasma() const;
    void moverfantasma();
    void choquepacman();
};
fantasma::fantasma(int x, int y) {
    _x = x;
    _y = y;
    fdir = rand() % 4;
    enemigo = al_create_bitmap(30, 30);
    enemigo = al_load_bitmap("enemigo.bmp");
}
void fantasma::dibujarfantasma() const {
    al_draw_bitmap_region(enemigo, dir * 33, 0, 0, 0, 30, 30, 0);
    al_draw_bitmap(enemigo, _x, _y, 0);
}

void fantasma::choquepacman() {
    if ((py == _y && px == _x) || (_y == anteriorpy && _x == anteriorpx)) {
        for (int j = 0; j <= 5; j++) {
            al_destroy_bitmap(pacman);
            al_destroy_bitmap(buffer);
            dibujarmapa();

            al_draw_bitmap_region(muerte, j * 33, 0, 0, 0, 33, 33, 0);
            al_draw_bitmap(pacman, px, py, 0);

            pantalla();
            //al_rest(80);
        }
        px = 30 * 14;
        py = 30 * 17;
        dir = 4;
    }
}
void fantasma::moverfantasma() {
    dibujarfantasma();
    choquepacman();
    if (mapa[_y / 30][_x / 30] == '|') {
        fdir = rand() % 4;
    }


    if (fdir == 0) {
        if (mapa[_y / 30][(_x - 30) / 30] != 'X')_x -= 30;
        else fdir = rand() % 3;
    }
    else if (fdir == 1) {
        if (mapa[_y / 30][(_x + 30) / 30] != 'X')_x += 30;
        else fdir = rand() % 3;
    }
    if (fdir == 2) {
        if (mapa[_y - 30 / 30][(_x) / 30] != 'X')_y -= 30;
        else fdir = rand() % 4;
    }
    if (fdir == 3) {
        if (mapa[_y + 30 / 30][(_x) / 30] != 'X')_y += 30;
        else fdir = rand() % 4;
    }
    //rutina atajo

    if (_x <= -30) {
        _x = 870;
    }
    else if (_x >= 870) _x = -30;
}



int main(int argc, char **argv) {
    if (!al_init()) {
        fprintf(stderr, "failed to initialize allegro!\n");
        return -1;
    }

    ALLEGRO_DISPLAY *display = NULL;

    al_set_new_display_flags(ALLEGRO_WINDOWED | ALLEGRO_RESIZABLE);
    display = al_create_display(ScreenWidth, ScreenHeight);
    al_set_window_position(display, 200, 100);
    al_set_window_title(display, "SAME");
    display = al_create_display(800, 600);

    ALLEGRO_KEYBOARD_STATE keyState;
    /*ALLEGRO_TIMER *timer;
    ALLEGRO_EVENT_QUEUE *event_queue;*/

    al_init();
    al_install_keyboard();
    al_init_font_addon();

    /*int game_initialized;
    int FPS = 60.0;
    int game_active;
    int can_change;*/
    buffer = al_create_bitmap(880, 600); //EJE X y Y POR 30
    roca = al_load_bitmap("roca.bmp");
    pacman = al_load_bitmap("pacman.bmp");
    pacman = al_create_bitmap(33, 33);
    comida = al_load_bitmap("comida.bmp");
    muerte = al_load_bitmap("muerte.bmp");


    al_set_target_backbuffer(display);

    ALLEGRO_COLOR electricBlue = al_map_rgb(44, 117, 255);
    /*ALLEGRO_TIMER *timer = al_create_timer(1.0 / FPS);
    ALLEGRO_EVENT_QUEUE *event_queue = al_create_event_queue();
    al_register_event_source(event_queue, al_get_display_event_source(display));
    al_register_event_source(event_queue, al_get_keyboard_event_source());
    al_register_event_source(event_queue, al_get_timer_event_source(timer));
    al_start_timer(timer); //novariables after this
    ALLEGRO_KEYBOARD_STATE keyState;*/
    al_draw_bitmap(buffer, 0, 0, 0);
    al_flip_display();


    fantasma A(30 * 2, 30 * 3);
    fantasma B(30 * 15, 30 * 15);
    fantasma C(30 * 2, 30 * 3);
    fantasma D(30 * 15, 30 * 15);
    fantasma E(30 * 2, 30 * 3);
    fantasma F(30 * 15, 30 * 15);
    fantasma G(30 * 2, 30 * 3);
    fantasma H(30 * 15, 30 * 15);

    while (!al_key_down(&keyState, ALLEGRO_KEY_ESCAPE) && gameover()) {
        //ALLEGRO_EVENT events;
        //al_wait_for_event(event_queue, &events);
        al_get_keyboard_state(&keyState);

        anteriorpx = px;
        anteriorpy = py;

        if (al_key_down(&keyState, ALLEGRO_KEY_DOWN))
        {
            dir = 3;
        }
        else if (al_key_down(&keyState, ALLEGRO_KEY_UP))
        {
            dir = 2;
        }

        else if (al_key_down(&keyState, ALLEGRO_KEY_RIGHT))
        {
            dir = 1;
        }

        else if (al_key_down(&keyState, ALLEGRO_KEY_LEFT))
        {
            dir = 0;

        }
        if (dir == 0)
        {
            if (mapa[py / 30][(px - 30) / 30] != 'X') {
                px -= 30;

            }
        }
        else {
            dir = 4;
        }

        if (dir == 1) {
            if (mapa[py / 30][(px + 30) / 30] != 'X') {
                px += 30;
            }
        }
        else dir = 4;

        if (dir == 2) {
            if (mapa[py / 30][(px - 30) / 30] != 'X') {
                px -= 30;
            }
        }
        else dir = 4;

        if (dir == 3) {
            if (mapa[py / 30][(px + 30) / 30] != 'X') {
                px += 30;
            }
        }
        else dir = 4;

        //rutina para atajo
        if (px <= -30) {
            px = 870;
        }
        else if (px >= 870) {
            px = -30;
        }
        al_destroy_bitmap(buffer);
        dibujarmapa();
        pantalla();
        dibujarpersonaje();
        A.moverfantasma();
        B.moverfantasma();
        C.moverfantasma();
        D.moverfantasma();
        E.moverfantasma();
        F.moverfantasma();
        G.moverfantasma();
        H.moverfantasma();

        al_destroy_bitmap(pacman);
        al_draw_bitmap_region(pacman, 4 * 33, 0, 0, 0, 33, 33, 0);
        al_draw_bitmap(pacman, px, py, 0);
        pantalla();
    };
    printf("\npresione la barra espaciadora y luego enter para continuar");
    while (getchar() != ' ');
    return 0;
}

Answer 1

SIGSEV is a memory out-of-bounds error, so you might want to check your boundary cases. Make sure your MAXFILAS and MAXCOLS are large enough. Could you show us your al_draw_bitmap function?

Answer 2

The answer is clear if you look closely at the output from your debugger.

The 'bitmap' parameter you passed to al_draw_tinted_bitmap is NULL (0x0).

Allegro may or may not crash if you pass it a NULL pointer, depends on how robust it's error checking is. Usually in debug mode, allegro will assert that the bitmap is not NULL.

So make sure all your bitmaps are valid (Non NULL) after loading and before passing them to any allegro drawing functions.