設置結構指針的整數會產生分段錯誤

Question

我正在傳遞一個指向結構的指針，並且我想將此結構的成員m和n設置為數字3和3 。 但是，我遇到了細分問題。 發生了什么？

#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;
}

這是使用堆棧內存的一種方法，您也可以malloc並使用堆內存

#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;
}

這些都應該起作用。