C:使用Free()

Question

我有一个指向结构的指针数组，一旦不再需要它们，我就尝试在它们上使用free()。下面是这些结构的设置方式：

typedef struct {
    SDL_Surface *sprite;
    SDL_Rect rect;
} Laser;

Laser *fireLaser(char *sprite, int x, int y) 
{
    Laser *laser = malloc(sizeof(Laser));

    laser->sprite = loadSurface(sprite);
    laser->rect.x = x;
    laser->rect.y = y;

    return laser;
}

game->playerLasers[player->laserCount++] = fireLaser("images/laser.bmp", (player->rect.x, player->rect.y);

一旦不再需要它，我就尝试在它上面使用free()。

SDL_FreeSurface(game->playerLasers[i]->sprite);
free(game->playerLasers[i]);

我用free(game->playerLasers[i]);编译它，没有得到任何警告或错误。程序会运行，但是一旦free()运行，我就会得到一个分段错误。

当我使用valgrind运行程序时，奇怪的是，我没有得到分段错误，但是一旦运行free()，我就得到了以下输出：

==2010== Invalid read of size 8
==2010==    at 0x4012D8: spawnGrunts (main.c:196)
==2010==    by 0x4013FC: updates (main.c:219)
==2010==    by 0x4016CD: main (main.c:277)
==2010==  Address 0xcfce9c0 is 0 bytes inside a block of size 32 free'd
==2010==    at 0x4C2AD90: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2010==    by 0x4012FF: spawnGrunts (main.c:197)
==2010==    by 0x4013FC: updates (main.c:219)
==2010==    by 0x4016CD: main (main.c:277)
==2010==  Block was alloc'd at
==2010==    at 0x4C29BBE: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2010==    by 0x400E65: loadGrunt (main.c:105)
==2010==    by 0x4011FE: spawnGrunts (main.c:182)
==2010==    by 0x4013FC: updates (main.c:219)
==2010==    by 0x4016CD: main (main.c:277)
==2010== 
==2010== Invalid free() / delete / delete[] / realloc()
==2010==    at 0x4C2AD90: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2010==    by 0x4012FF: spawnGrunts (main.c:197)
==2010==    by 0x4013FC: updates (main.c:219)
==2010==    by 0x4016CD: main (main.c:277)
==2010==  Address 0xcfce9c0 is 0 bytes inside a block of size 32 free'd
==2010==    at 0x4C2AD90: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2010==    by 0x4012FF: spawnGrunts (main.c:197)
==2010==    by 0x4013FC: updates (main.c:219)
==2010==    by 0x4016CD: main (main.c:277)
==2010==  Block was alloc'd at
==2010==    at 0x4C29BBE: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2010==    by 0x400E65: loadGrunt (main.c:105)
==2010==    by 0x4011FE: spawnGrunts (main.c:182)
==2010==    by 0x4013FC: updates (main.c:219)
==2010==    by 0x4016CD: main (main.c:277)

有没有人能给我一个提示？

Answer 1

在valgrind下运行您的程序，大部分时间不会崩溃，因为您是在valgrind创建的内存空间中运行的，可以说，valgrind对您的程序更具容错能力。

除非尝试释放非指针类型，否则通常不会出现编译错误。但它将在执行时崩溃，因为您将尝试释放一个错误的地址。

我非常有兴趣看到你负责释放thoose资源的功能，一个完整的。

您是否在任何地方跟踪数组的大小？是否将arrayi设置为NULL以表明它已被释放且不再可用？

当指针不可用时，请始终将其设置为空。