"Invalid read of size 4" 尝试重新分配内存时

Question

我正在编写一个贪吃蛇游戏作为第一个 "serious" C 项目。但是当我尝试培育贪吃蛇时，程序因 SEGFAULT 错误而崩溃。所以，我尝试运行 Valgrind 中的游戏，得到了这个：

==11312== 30 errors in context 7 of 7:
==11312== Invalid read of size 4
==11312==    at 0x10969E: collide (game.c:238)
==11312==    by 0x108FBD: main (game.c:120)
==11312==  Address 0x5897c60 is 0 bytes inside a block of size 40 free'd
==11312==    at 0x4C31D2F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==11312==    by 0x109724: snake_grow (game.c:250)
==11312==    by 0x108F7D: main (game.c:113)
==11312==  Block was alloc'd at
==11312==    at 0x4C31B25: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==11312==    by 0x109278: start (game.c:159)
==11312==    by 0x108EC0: main (game.c:91)
==11312== 
==11312== ERROR SUMMARY: 80 errors from 7 contexts (suppressed: 0 from 0)

正如我所建议的，我重新分配错误，这就是游戏崩溃的原因。所以，问题应该出在这里：

void snake_grow(snake_t *snake){
  snake->length++;
  snake->body = realloc(snake->body, sizeof(snake->body[0]) * (snake->length));
  snake->end = snake->body + snake->length - 1;
  snake->end->x = snake->prev_x;
  snake->end->y = snake->prev_y;
}

或者我只是在函数中使用了指针错误？

bool collide(snake_t *snake, block map[MAXY][MAXX]){
  bool ret = FALSE;
  if(map[snake->head->y][snake->head->x].collision == COLLIDABLE){
    ret = TRUE;
  }
  for(int i = 1; i < snake->length; i++){
    if(snake->body[i].x == snake->head->x){
      if(snake->body[i].y == snake->head->y){
    ret = TRUE;
      }
    }    
  }
  return ret;
}

奇怪，但我找不到与我的问题类似的问题。但也许我只是不明白解决方案。

Answer 1

偶然地，当我尝试制作最小的可重现示例并进行调试时，正如 WhozCraig 所建议的那样，我解决了这个问题。

void snake_grow(snake_t *snake){
  snake->length++;
  snake->body = realloc(snake->body, sizeof(snake->body[0]) * (snake->length));
  snake->end = snake->body + snake->length - 1;
  snake->end->x = snake->prev_x;
  snake->end->y = snake->prev_y;
}

这个函数除了重新分配内存之外，还为 snake->end 设置了新的地址。但是还有snake->head，在realloc之后指向同一个地址。所以，我需要做的就是将 snake->head 设置为新地址。

snake->head = snake->body;

"Invalid read of size 4" 尝试重新分配内存时

"Invalid read of size 4" when trying to realloc memory

c

valgrind