无法在函数调用中更改动态分配的数组值

Question

我在使用 C 时遇到一些问题。

我的任务是:

Create a dynamically allocated matrix (max 5x5), let the user fill in the values, then send it to a function along with an unallocated array (1D) which will be used to store all values of the matrix that are lower than the average of each row. The 1D array should be defined in the main function and allocated inside the function that finds the desired elements.

一切顺利，我制作了矩阵，并将其发送到上述函数，但我无法更改新分配的一维数组的值。

---

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

int lower_than_average(int **matrix, int **p, int m, int n) {
    int i, j, sum;
    float average;
    int count = 0, counter = 0;
    for (i = 0; i < m; i++) {
        sum = 0;

        for (j = 0; j < n; j++) sum += matrix[i][j];
        average = (float)sum / n;

        for (j = 0; j < n; j++){
            if (matrix[i][j] < average) count++;
        }
    }

    *p = (int*)malloc(count * sizeof(int));

    for (i = 0; i < m; i++) {
        sum = 0;
        for (j = 0; j < n; j++) sum += matrix[i][j];
        average = (float)sum / n;
        for (j = 0; j < n; j++) {
            if (matrix[i][j] < average) *p[counter++] = matrix[i][j];
        }
    }

    printf("\n\n");

    return(count);
}

void print_matrix(int **matrix, int m, int n) {
    int i, j;
    for (i = 0; i < m; i++) {
        for (j = 0; j < n; j++) {
            printf("%d ", matrix[i][j]);
        }
        printf("\n\n");
    }
}

int main(void) {
    int m, n, **matrix, *elements_a = NULL;
    int i, j, elements_a_size;

    do {
        printf("Enter the number of rows and columns [max 5x5]: ");
        scanf("%d %d", &m, &n);
    } while (n > 5 || n < 0 || m > 5 || m < 0);

    matrix = (int**)malloc(m * sizeof(int*)); // Alokacija redaka

    /*

        X | <empty>
        X | <empty>
        X | <empty>
        X | <empty>

    */

    for (i = 0; i < m; i++) matrix[i] = (int*)calloc(n, sizeof(int)); // Alokacija stupaca

    /*

        X | Y Y Y Y Y Y
        X | Y Y Y Y Y Y
        X | Y Y Y Y Y Y
        X | Y Y Y Y Y Y

    */

    for (i = 0; i < m; i++) {
        for (j = 0; j < n; j++) {
            printf("Enter [%d][%d] element: ", i, j);
            scanf("%d", &matrix[i][j]);
        }
    }

    printf("\n\n");

    print_matrix(matrix, m, n);

    elements_a_size = lower_than_average(matrix, &elements_a, m, n);

    printf("\nElements of rows smaller than the row average value: ");
    for (i = 0; i < elements_a_size; i++) printf("%d ", elements_a[i]);

    for (i = 0; i < m; i++) free(matrix[i]);
    free(matrix);

    return 0;
}

对于输入:3 3 然后 1 2 3 4 5 6 7 8 9 它几乎不输出任何内容。

**p and *p[0] 

代替

*p[counter++]

它输出这个:7 -2467754 -2467754

我做错了什么？我认为分配是正确的，我可以访问 *(p + n) 但它什么也没做...

Answer 1

你必须换行

 *p[counter++] = matrix[i][j];

通过

 (*p)[counter++] = matrix[i][j];

因为[]优先于*

参见:Operator priorities in c/c++