动态分配/释放2D& 3D阵列 [英] dynamic allocation/deallocation of 2D & 3D arrays
问题描述
使用这种知识和一些对称性，我想出了以下代码。
（在编码时我很难在3D中进行可视化）。
请评论正确性，并建议任何更好的选择（效率或直觉），如果有的话。
另外，我认为这两个2D像数组arr2D [2] [3]和
arr3D [2] [3] [2]这样的静态数组就可以正常访问3D数组。对？
2D代码
//分配2D数组
int ** allocate2D（int rows，int cols）
{
int ** arr2D;
int i;
arr2D =（int **）malloc（rows * sizeof（int *））; （i = 0; i< rows; i ++）
{
arr2D [i] =（int *）malloc（cols * sizeof（int））;
}
}
//取消分配2D数组
void deallocate2D（int ** arr2D，int rows）
{
int i ; （i = 0; i< rows; i ++）
{
free（arr2D [i]）;
}
免费（arr2D）;
}
3D代码
//分配一个3D数组
int *** allocate3D（int l，int m，int n）
{
int *** arr3D ;
int i，j，k;
arr3D =（int ***）malloc（l * sizeof（int **））;
for（i = 0; i
arr3D [i] =（int **）malloc（m * sizeof（int *））;
for（j = 0; j< m; j ++）
{
arr3D [i] [j] =（int *）malloc（n * sizeof（int））;
}
}
return arr3D;
}
//取消分配3D数组
void deallocate3D（int arr3D，int l，int m）
{
int i，j; （i = 0; i
{
for（int j = 0; j< m; j ++）
{
自由（arr3D [i] [j]）;
}
free（arr3D [i]）;
}
free（arr3D）;
}
您还可以分配一个数组并计算个体指数。这需要更少的分配器调用，并且导致更少的碎片和更好的缓存使用。
typedef struct {
int a;
int b;
int * data;
} Int2d;
Int2d arr2d = {2，3};
arr2d.data = malloc（arr2d.a * arr2d.b * sizeof * arr2d.data）;
现在 arr2d [r] [c] 成为 arr2d.data [r * arr2d.b + c] 。交易是一个单独的（）离开。作为一个奖励，你一定会永远保持你的动态数组大小。
Extrapolating to 3d：
typedef struct {
int a;
int b;
int c;
int * data;
} Int3d;
Int3d arr3d = {2，3，4};
arr3d.data = malloc（arr3d.a * arr3d.b * arr3d.c * sizeof * arr3d.data）;
// arr3d [r] [c] [d]
//变为：
arr3d.data [r *（arr3d.b * arr3d.c）+ c * arr3d.c + d];
您应该将这些索引操作（以及该事项的（除）分配）封装在一个单独的函数或宏。
（r，c和d的名称可能更好，我正在进行行，列和深度，而a，b和c是它们相应尺寸的极限，你可能喜欢这样的n1，n2，n3，甚至使用一个数组。）
I know about algorithms to allocate/deallocate a 2D array dynamically, however I'm not too sure about the same for 3D arrays.
Using this knowledge and a bit of symmetry, I came up with the following code.
(I had a hard time visualizing in 3D during coding).
Please comment on the correctness and suggest any better alternative (efficiency-wise or intuitively), if any.
Also, I think both these 2D and 3D arrays can be accessed normally like static arrays like arr2D[2][3] and
arr3D[2][3][2]. Right?
Code for 2D
//allocate a 2D array
int** allocate2D(int rows,int cols)
{
int **arr2D;
int i;
arr2D = (int**)malloc(rows*sizeof(int*));
for(i=0;i<rows;i++)
{
arr2D[i] = (int*)malloc(cols*sizeof(int));
}
}
//deallocate a 2D array
void deallocate2D(int** arr2D,int rows)
{
int i;
for(i=0;i<rows;i++)
{
free(arr2D[i]);
}
free(arr2D);
}
Code for 3D
//allocate a 3D array
int*** allocate3D(int l,int m,int n)
{
int ***arr3D;
int i,j,k;
arr3D = (int***)malloc(l * sizeof(int **));
for(i=0;i<l;i++)
{
arr3D[i] = (int**)malloc(m * sizeof(int*));
for(j=0;j<m;j++)
{
arr3D[i][j] = (int*)malloc(n*sizeof(int));
}
}
return arr3D;
}
//deallocate a 3D array
void deallocate3D(int arr3D,int l,int m)
{
int i,j;
for(i=0;i<l;i++)
{
for(int j=0;j<m;j++)
{
free(arr3D[i][j]);
}
free(arr3D[i]);
}
free(arr3D);
}
You can also allocate one array and compute individual indices. This requires fewer allocator calls and results in both less fragmentation and better cache use.
typedef struct {
int a;
int b;
int* data;
} Int2d;
Int2d arr2d = { 2, 3 };
arr2d.data = malloc(arr2d.a * arr2d.b * sizeof *arr2d.data);
Now arr2d[r][c] becomes arr2d.data[r * arr2d.b + c]. Deallocation is a single free() away. As a bonus you're sure to always keep your dynamic array sizes with you.
Extrapolating to 3d:
typedef struct {
int a;
int b;
int c;
int* data;
} Int3d;
Int3d arr3d = { 2, 3, 4 };
arr3d.data = malloc(arr3d.a * arr3d.b * arr3d.c * sizeof *arr3d.data);
//arr3d[r][c][d]
// becomes:
arr3d.data[r * (arr3d.b * arr3d.c) + c * arr3d.c + d];
You should encapsulate these index operations (and the (de-)allocations for that matter) in a separate function or macro.
(The names for r, c, and d could be better—I was going for row, column, and depth. While a, b, and c are the limits of their corresponding dimensions, you might prefer something like n1, n2, n3 there, or even use an array for them.)
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