正确的方式免费M * n矩阵二维分配 [英] correct way to free m*n matrix bidimensional allocation

问题描述

我分配在这样一个非方阵，但我不知道如果我正确地使用释放

I allocate a non-square matrix in this way, but I'm not sure if I'm using the deallocation correctly

float **matrix_alloc(int m /* rows */, int n /* columns */)
{
    int i;
    float **arr = malloc(m*sizeof(*arr));
    for(i=0; i<m; i++)
    {
        arr[i]=malloc(n*sizeof(**arr));
    }
    return arr;
}

我试图释放内存双向

I have tried two way to free the memory

-Attempt A 循环行

void free_mem_mat(int m, float **array) {
    int i;
    for (i = 0; i < m; i++) {
        free(array[i]);
    }
    free(array);
}

- 尝试乙循环的列

void free_mem_mat(int n, float **array) {
    int i;
    for (i = 0; i < n; i++) {
        free(array[i]);
    }
    free(array);
}

我应该怎么用自由？顺便：一种对行或方式 乙？ （我知道书面方法是我重写这是最明显的可能是相同的）

what should I use to free? the way A on the rows or the way B? (I know as written the method is the same I have rewritten this to be most clear possible)

推荐答案

您需要有一个免费（）每个的malloc（） ^* 。有 M + 1 来电的malloc（）;你最好 M + 1 来电免费（）了。

You need one free() for each malloc()^*. There were m+1 calls to malloc(); you'd better make m+1 calls to free() too.

由于为出发点，选项A是正确的解决方案。然而，这也是公平地注意到这两个功能（选项A和选项B）是完全等同，只要你传递给分配函数作为在 M 尺寸在释放函数的大小参数。在选项B中的评论是一种误导;你不遍历列。

Given that as the starting point, option A is the correct solution. However, it is also fair to note that the two functions (option A and option B) are strictly equivalent as long as you pass the m dimension given to the allocation function as the size argument of the deallocation function. The comment in option B is misleading; you're not looping over columns.

假设：

enum { MAT_ROWS = 20, MAT_COLS = 30 };
float **matrix = matrix_alloc(MAT_ROWS, MAT_COLS);

正确调用 free_mem_mat（）是：

free_mem_mat(MAT_ROWS, matrix);

---

^{*这是一个过于简单化的说法，如果你使用的realloc（）或释放calloc（） 。你需要一个免费（）每个的malloc（）这不是 realloc（）的'D，和免费（）每个的realloc（）未做免费（）＆MDASH;由大小设置为0款待释放calloc（）等同于的malloc（）据免费（）而言}

---

^{* This is an over-simplified statement if you use realloc() or calloc(). You need a free() for each malloc() that was not realloc()'d, and a free() for each realloc() that did not do a free() — by setting the size to 0. Treat calloc() as equivalent to malloc() as far as free() is concerned.}

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