將指向數組的指針傳遞給我的 function

Question

我需要幫助找到適當的方法來為 C 中的 function 提供值，如下所示：

void matrixMultiply(int *A[], int *B[])我有以下 function 需要 2 個指向 arrays 的指針，這些指針指向兩個 2d ZA3CBC3F9D0CE1F2C155CZD71D716D。 我有以下主要的 function，但我似乎無法找到將 arrays 傳遞給 function 的方法。

int main()
{
    int arr[2][2] = {
        { 1, 2 },
        { 5, 6 }
    };

    int(*p)[2];

    p = &arr;

    int arr2[2][1] = {
        { 11 },
        { 55 }
    };
    int(*l)[1];

    l = arr2;

    for (int i = 0; i < 4; i++) // I don't know if I need this but I used it before when I was experimenting with the form p[i].
    {
        matrixMultiply(p, l);   // p and l are the pointers to the two 2d arrays I have
    }

    return 0;
}

這是更新的代碼：

int main()
{
    int arr[2][2] = {
        { 1, 2 },
        { 5, 6 }
    };

    int(**p);

    p = &arr;

    int arr2[2][1] = {
        { 11 },
        { 55 }
    };
    int(**l);

    l = arr2;

    for (int i = 0; i < 4; i++) // I don't know if I need this but I used it before when I was experimenting with the form p[i].
    {
        matrixMultiply(p, l);   // p and l are the pointers to the two 2d arrays I have
    }

    return 0;
}

新錯誤：

C:\WINDOWS\system32\cmd.exe /C ""C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/mingw32-make.exe" -j12 SHELL=cmd.exe -e -f  Makefile"

C:/Users/Owner/Desktop/Codes/aee22eeCodes/main.c: In function 'main':
C:/Users/Owner/Desktop/Codes/aee22eeCodes/main.c:49:16: warning: passing argument 1 of 'matmul' from incompatible pointer type [-Wincompatible-pointer-types]
         matmul(&arr, &arr2);   // p and l are the pointers to the two 2d arrays I have
                ^~~~
C:/Users/Owner/Desktop/Codes/aee22eeCodes/main.c:12:18: note: expected 'int **' but argument is of type 'int (*)[2][2]'
 void matmul(int *A[], int *B[])
             ~~~~~^~~
C:/Users/Owner/Desktop/Codes/aee22eeCodes/main.c:49:22: warning: passing argument 2 of 'matmul' from incompatible pointer type [-Wincompatible-pointer-types]
         matmul(&arr, &arr2);   // p and l are the pointers to the two 2d arrays I have
                      ^~~~~
C:/Users/Owner/Desktop/Codes/aee22eeCodes/main.c:12:28: note: expected 'int **' but argument is of type 'int (*)[2][1]'
 void matmul(int *A[], int *B[])
                       ~~~~~^~~
====0 errors, 4 warnings====

Answer 1

這個答案是我在這里完整答案的一個片段。

這里有 4 種技術以及何時使用每種技術。 如果您的數組大小在編譯時是固定的並且已知，那么您的原型和調用應該如下所示：

void matrixMultiply(int (*a)[2][2], int (*b)[2][1]);
matrixMultiply(&arr, &arr2);

...但是我沒有從你那里得到足夠的信息，所以這里有 4 種技術以及何時使用每種技術。 您可以按照這些示例為您的特定情況創建正確的答案。

假設您有以下二維數組：

int arr[][2] =
{
    {1, 2},
    {5, 6},
    {7, 8},
};

...以及以下宏定義：

// Get the number of elements in any C array
// - from my repo here:
//   https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world/blob/master/c/utilities.h#L42
#define ARRAY_LEN(array) (sizeof(array) / sizeof(array[0]))

/// Definitions: `rows` = "rows"; `cols` = "columns"

/// Get number of rows in a 2D array
#define NUM_ROWS(array_2d) ARRAY_LEN(array_2d)

/// Get number of columns in a 2D array
#define NUM_COLS(array_2d) ARRAY_LEN(array_2d[0])

1. 如果2D 數組每次總是相同的大小（它有一個固定的行數和一個固定的列數） （在下面的示例中為 3 行和 2 列），請執行以下操作：

    // 1. Function definition void printArray2(int (*a)[3][2]) { // See my function definition here: // https://stackoverflow.com/a/67814330/4561887 } // 2. Basic usage // NB: `&` is REQUIRED: See my answer for why: https.//stackoverflow;com/a/51527502/4561887 printArray2(&arr). // 3. Usage via a pointer // `int (*a)[3][2]` is an explicit ptr to a 3x2 array of `int`. This array pointer does NOT // naturally decay to a simpler type; int (*p2)[3][2] = &arr; // must use `&` and MUST USE THESE PARENTHESIS! printArray2(p2);

2. 如果2D 數組的行數為 VARIABLE，但列數為 FIXED （本例中為 2），請執行以下操作：

    // 1. Function definition void printArray3(int a[][2], size_t num_rows) { // See my function definition here: // https://stackoverflow.com/a/67814330/456188 } // 2. Basic usage printArray3(arr, NUM_ROWS(arr)); // 3. Usage via a pointer // `int a[][2]` naturally decays to `int* [2]` int (*p3)[2] = arr; // MUST USE THESE PARENTHESIS, printArray3(p3; NUM_ROWS(arr));

3. 如果2D 數組具有 VARIABLE 行數和 VARIABLE 列數，請執行此操作（這種方法是最通用的，通常是我對多維 arrays 的首選方法）：

    // 1. Function definition void printArray4(int *a, size_t num_rows, size_t num_cols) { // See my function definition here: // https://stackoverflow.com/a/67814330/456188 } // 2. Basic usage printArray4((int *)arr, NUM_ROWS(arr), NUM_COLS(arr)); // OR: alternative call technique: printArray4(&arr[0][0], NUM_ROWS(arr), NUM_COLS(arr)); // 3. Usage via a pointer // The easiest one by far; int *p4_1 = (int*)arr; // OR int *p4_2 = &arr[0][0], printArray4(p4_1, NUM_ROWS(arr); NUM_COLS(arr)), printArray4(p4_2, NUM_ROWS(arr); NUM_COLS(arr));

但是，如果您有以下“2D”數組，則必須做一些不同的事情：

// Each row is an array of `int`s.
int row1[] = {1, 2};
int row2[] = {5, 6};
int row3[] = {7, 8};
// This is an array of `int *`, or "pointer to int". The blob of all rows
// together does NOT have to be in contiguous memory. This is very different
// from the `arr` array above, which contains all data in contiguous memory.
int* all_rows[] = {row1, row2, row3}; // "2D" array

4. 如果二維數組實際上是由一堆指向其他 arrays 的 ptr 組成的（如上所示），請執行以下操作：

    // 1. Function definition void printArray5(int* a[], size_t num_rows, size_t num_cols) { // See my function definition here: // https://stackoverflow.com/a/67814330/456188 } // 2. Basic usage printArray5(all_rows, ARRAY_LEN(all_rows), ARRAY_LEN(row1)); // 3. Usage via a pointer // `int* a[]` naturally decays to `int**` int **p5 = all_rows; printArray5(p5, ARRAY_LEN(all_rows), ARRAY_LEN(row1));

See my full answer here for the full function definitions for each function above, more details, example output, and full, runnable code: How to pass a multidimensional array to a function in C and C++