Malloc 内部结构失效 function

Question

I have a struct:

typedef struct cellNode {
        int cell;
        struct cellNode* next;
}   Node;

typedef struct  {
        int numRows;
        int numColumns;
        Node** rows;
}   Matrix;

and a function to add nodes in my code, but I get the 0xC0000005 error when i try to allocate memory for the node inside the function:

Node* createNode()
{
    int n;
    Node* newNode = malloc(sizeof(Node));
    if (newNode==NULL)
        exit(1);
    scanf("%d",&n);
    printf("n is %d\n",n);
    newNode->cell=n;
    newNode->next = NULL;
    return newNode;
}

The function allocates memory for a node and returns it to another function that appends it to an array of nodes. so the call for the createNode function looks like this:

Matrix* MatrixAdder(int row, int col, char mat)
{
    int i,j;
    int value=0;
    Node* newNode=NULL;
    Matrix* temp = malloc(sizeof(Matrix));
    if (temp==NULL)
        exit (1);
    temp->numRows=row;
    temp->numColumns=col;
    temp->rows = malloc(row * sizeof(Node*));
    if (temp->rows==NULL)
        exit(1);
    for (i=0;i<row;i++)
    {
        printf("Enter row %d data\n",i);
        scanf("%d",&value);
        temp->rows[i]->cell=value;
        for (j=0;j<col-1;j++)
        {

            newNode=createNode();
            temp->rows[i]->next=newNode;
            
        }
    }


}

I get this:

Enter row 0 data
2

Process returned -1073741819 (0xC0000005)   execution time : 6.525 s
Press any key to continue.

the function is able to receive the int but immediately fails at the malloc line. the main just calles for the functions:

int main()

{
    int i;
    Matrix *A, *B, *C;
    int n,m,k;
    MatSize(&n,&m,&k); /*works fine*/
    A=MatrixAdder(n, m, 'A');
    B=MatrixAdder(m, k, 'B');

    return 1;
}

Answer 1

This line

temp->rows[i]->cell=value;

is wrong. temp->rows[i] is not pointing to any valid object.

You did allocate memory for rows , ie

temp->rows = malloc(row * sizeof(Node*));

but you never assigned any values to row[0], row[1], ... so you are dereferencing uninitialized pointers.

Answer 2

Works here:

---

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

typedef struct cellNode {
        int cell;
        struct cellNode *next;
}   Node;

// and a function to add nodes in my code, but I get the 0xC0000005 error when i try to allocate memory for the node inside the function:

Node *createNode()
{
    int n;
    Node *newNode = malloc(sizeof(Node));
    if (newNode==NULL)
        exit(1);
    scanf("%d",&n);
    printf("n is %d\n",n);
    newNode->cell=n;
    newNode->next = NULL;
    return newNode;
}

// The function allocates memory for a node and returns it to another function that appends it to an array of nodes. so the call for the createNode function looks like this :

int main(void)
{
Node *someNode=NULL;

printf("Enter row 0 data\n");
someNode = createNode();

printf("Some node: %d\n", someNode->cell);

return 0;
}