在C中为3D数组分配连续内存 [英] Allocating contiguous memory for a 3D array in C

问题描述

我需要为3D数组分配连续的空间. ()我想我应该在第一位置做到这一点，但是在实际的生产代码中，直到运行时我才知道数组的尺寸.我在下面的玩具代码中将它们作为常量提供，只是为了使事情保持简单.我知道坚持使用连续空间的潜在问题，但我只需要拥有它.我已经看到了如何对2D数组执行此操作，但是显然我不理解如何将图案扩展到3D.当我调用该函数释放内存free_3d_arr时，出现错误:

I need to allocate contiguous space for a 3D array. () I GUESS I SHOULD HAVE MADE THIS CLEAR IN THE FIRST PLACE but in the actual production code, I will not know the dimensions of the array until run time. I provided them as constants in my toy code below just to keep things simple. I know the potential problems of insisting on contiguous space, but I just have to have it. I have seen how to do this for a 2D array, but apparently I don't understand how to extend the pattern to 3D. When I call the function to free up the memory, free_3d_arr, I get an error:

lowest lvl
mid lvl
a.out(2248,0x7fff72d37000) malloc: *** error for object 0x7fab1a403310: pointer being freed was not allocated

如果有人能告诉我解决方法，将不胜感激.代码在这里:

Would appreciate it if anyone could tell me what the fix is. Code is here:

#include <stdio.h>
#include <stdlib.h>

int ***calloc_3d_arr(int sizes[3]){

   int ***a;
   int i,j;

   a = calloc(sizes[0],sizeof(int**)); 
   a[0] = calloc(sizes[0]*sizes[1],sizeof(int*));
   a[0][0] = calloc(sizes[0]*sizes[1]*sizes[2],sizeof(int));

   for (j=0; j<sizes[0]; j++) {
      a[j] = (int**)(a[0][0]+sizes[1]*sizes[2]*j);
      for (i=0; i<sizes[1]; i++) {
         a[j][i] = (int*)(a[j]) + sizes[2]*i;
      }
   }

   return a;

}



void free_3d_arr(int ***arr) {

   printf("lowest lvl\n");
   free(arr[0][0]);
   printf("mid lvl\n");
   free(arr[0]);         // <--- This is a problem line, apparently.
   printf("highest lvl\n");
   free(arr);

}



int main() {

   int ***a;
   int sz[] = {5,4,3};
   int i,j,k;

   a = calloc_3d_arr(sz);

   // do stuff with a

   free_3d_arr(a);

}

推荐答案

由于您使用的是C语言，因此建议您使用真正的多维数组:

Since you are using C, I would suggest that you use real multidimensional arrays:

int (*a)[sz[1]][sz[2]] = calloc(sz[0], sizeof(*a));

这将为您的3D阵列分配连续存储.请注意，从C99开始，尺寸可以是动态的.您完全可以像使用指针数组那样访问此数组:

This allocates contiguous storage for your 3D array. Note that the sizes can be dynamic since C99. You access this array exactly as you would with your pointer arrays:

for(int i = 0; i < sz[0]; i++) {
    for(int j = 0; j < sz[1]; j++) {
        for(int k = 0; k < sz[2]; k++) {
            a[i][j][k] = 42;
        }
    }
}

但是，引擎盖下没有指针数组，索引是通过指针算术和数组指针衰减的魔术来完成的.而且由于使用单个calloc()来分配事物，因此单个free()足以摆脱它:

However, there are no pointer arrays under the hood, the indexing is done by the magic of pointer arithmetic and array-pointer-decay. And since a single calloc() was used to allocate the thing, a single free() suffices to get rid of it:

free(a);    //that's it.

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