c - 设置结构指针的整数会导致段错误

Question

我正在传递一个指向结构的指针，我想将这个结构的成员 m 和 n 设置为数字 3 并且3。但是，我遇到了段错误。发生了什么事？

#include <stdio.h>

typedef struct Matrix {
    int m; //number of lines
    int n; //number of columns
    float* numbers; //elements of our matrix
} Matrix;

void matrix_create(Matrix* a, const float *array, int lines, int columns)
{   
    a->m = lines;
    a->n = columns;
}


int main()
{
    Matrix* a;
    float b[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
    matrix_create(a, b, 3, 3);
    return 0;
}

Answer 1

#include <stdio.h>

typedef struct Matrix {
    int m; //number of lines
    int n; //number of columns
    float* numbers; //elements of our matrix
} Matrix;

void matrix_create(Matrix* a, const float *array, int lines, int columns)
{   
    a->m = lines;
    a->n = columns;
}


int main()
{
    Matrix* a;
    Matrix temp;//Stack Matrix
    float b[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
    a = &temp; //Stack memory
    matrix_create(a, b, 3, 3);
    return 0;
}

这里有一种使用栈内存的方法，你可以 malloc 也可以使用堆内存

#include <stdio.h>

typedef struct Matrix {
    int m; //number of lines
    int n; //number of columns
    float* numbers; //elements of our matrix
} Matrix;

void matrix_create(Matrix* a, const float *array, int lines, int columns)
{   
    a->m = lines;
    a->n = columns;
}


int main()
{
    Matrix* a = malloc(sizeof(Matrix));
    float b[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
    matrix_create(a, b, 3, 3);
    return 0;
}

这些都应该有效。