英文:
C Pointer to a dynamic array of type int(*)[row] inside where row is unalocated inside of struct
问题
以下是您要翻译的内容：
基本上，我想要有一个结构体，可以在其中放置数据和一个数组。
我知道使用int**然后malloc一个指针数组的方法，然后在每个指针上进行malloc。
但这不是我想要的。原因是从技术上讲，这会更慢，因为（某种原因，缓存方面的问题）。
此外，它允许数据不被分散。
如果我成功运行它，我将拥有创建动态2D数组并可以放置在结构体内的最佳方法。
以下是几乎完成的代码示例。
我知道这与已经提出的问题相似，甚至与我早期提出的问题相似，但我要求的是不同的答案。
（创建一个可以放置在结构体内的任意大小（行、列）2D数组的最佳可能方法（在堆上，使用动态内存分配malloc...），以便该数组是可以连续存储在内存中的数据类型。如果数据可以连续存储在内存中，则加分。）
#include <stdio.h>#include <stdlib.h>typedef struct {int row;int col;int *(data)[];} iMAT;iMAT* create_matrix(int row, int col) {iMAT* matrix = malloc(sizeof(iMAT));int (*arr)[row] = malloc(sizeof(int[col][row]));matrix->row = row;matrix->col = col;matrix->data = arr;return matrix;}int main() {int row = 5;int col = 5;iMAT* matrix = create_matrix(row, col);return 0;}
请注意，我已将代码翻译为中文，如您所要求。
英文:
Basically, I want to have a struct where I can put data and an array.
I know the method of using int** and then malloc an array of pointer.
then malloc at each pointer.
But that's not what I want. The reasons is that technically, this would be slower because (something something caching).
Also, it allows the data to not be fragmented.
And if I get it running, I will have the definitive best way to create a dynamic 2D array that can be placed inside a struct.
Here is an example of the nearly finished code.
I know this is similar to already asked question, even similar to a question I asked early on, but what I'm asking for is a different answer.
(What is the best possible way to create a 2d array of arbirtrary size (row, col) on the heap (dynamic memory, malloc...), such that this array is a data type that can be contained within a struct. Bonus point if the data can be stored consequitively on the memory.)
#include <stdio.h>#include <stdlib.h>typedef struct {int row;int col;int *(data)[];} iMAT;iMAT* create_matrix(int row, int col) {iMAT* matrix = malloc(sizeof(iMAT));int (*arr)[row] = malloc(sizeof(int[col][row]));matrix->row = row;matrix->col = col;matrix->data = arr;return matrix;}int main() {int row = 5;int col = 5;iMAT* matrix = create_matrix(row, col);return 0;}
答案1
得分: 2
这不会编译，因为这个结构体成员：
int *(data)[];
是一个指针数组，意味着这个赋值语句：
matrix->data = arr;
试图赋值给一个数组，这是不允许的。你想要的是一个指向未指定大小数组的指针：
int (*data)[];
然而请注意，由于指向的类型是不完整的，你将无法直接访问数组成员。要读取或写入数组成员，你需要将其强制转换为正确的类型：
((int (*)[matrix->cols])matrix->data)[1][2] = 4;
或者将其分配给正确类型的临时变量并使用该变量：
data[1][2] = 4;```<details><summary>英文:</summary>This doesn't compile because this struct member:int *(data)[];Is an array of pointers, meaning that this:matrix->data = arr;Is an assignment to an array which is not allowed. What you wanted was a pointer to an array of unspecified size:int (*data)[];Note however that you won't be able to access the array members directly because the pointed-to type is incomplete. To read or write members of the array, you'd either need to cast it to the proper type:((int (*)[matrix->cols])matrix->data)[1][2] = 4;Or assign it to a temporary of the proper type and use that:int (*data)[matrix->col] = matrix->data;data[1][2] = 4;</details>
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