C: Heap block at ### modified at ### past requested size of ### - c

Question

So I'm storing a 2D dynamic Array into a matrix struct:
struct Matrix {
int ncol;
int nrow;
double **mat;
};
typedef struct Matrix Matrix;
I then have a function that takes the contents from a 2D array and stores it into the matrix:
// Initializes matrix mat whose values are the passed in 2D array
// Made Matrix **mat a double pointer so that I can initialize the Matrix *pointer from Main
void matrix_initializeFromArray(Matrix **mat, int nrow, int ncol, double array[][ncol]) {
(*mat) = (Matrix*) malloc(sizeof(Matrix*));
(*mat)->mat = (double**) malloc(nrow*sizeof(double*));
for(int i = 0; i < nrow; i++) {
(*mat)->mat[i] = (double*) malloc(ncol*sizeof(double*));
for(int j = 0; j < ncol; j++) { // intialize all values to array values
(*mat)->mat[i][j] = array[i][j];
}
}
(*mat)->ncol = ncol;
(*mat)->nrow = nrow;
}
Where this is the destructor for the matrix:
// Destructor
void matrix_destructor(Matrix **mat) {
for(int i = 0; i < (*mat)->nrow; i++) {
free((*mat)->mat[i]);
}
free((*mat)->mat);
free(*mat);
}
A small example of this is the following:
void main() {
Matrix *temp;
double array[1][1];
array[0][0] = 34;
matrix_initializeFromArray(&temp, 1, 1, array);
matrix_print(temp);
matrix_destructor(&temp);
}
This code executes normally on gdb and valgrind in my Linux Ubuntu but for some reason it creates this error while I run it on Windows.
warning: HEAP[a.exe]:
warning: Heap block at 00B51710 modified at 00B5171C past requested size of 4
I ran through the gdb on Windows and it occurs at this line in the destructor on the first loop: free((*mat)->mat[i]);
Any Help?

Answer 1

I have simplified your code, matrix_print is missing
The issue was with the malloc
when you allocate something you get a pointer to the memory, for example
malloc(sizeof(double)); returns a pointer to a memory area that can store a double so a double *
malloc(sizeof(double*)); returns a pointer to a memory are that can store a pointer to a double, so a double **`
#include <stdio.h>
#include <stdlib.h>
struct Matrix {
int ncol;
int nrow;
double **mat;
};
typedef struct Matrix Matrix;
void matrix_initializeFromArray(Matrix *mat, int nrow, int ncol, double array[][ncol]) {
mat->ncol = ncol;
mat->nrow = nrow;
mat->mat = malloc(nrow * sizeof(double*));
for(int i = 0; i < nrow; i++) {
mat->mat[i] = malloc(ncol*sizeof(double));
for(int j = 0; j < ncol; j++) { // intialize all values to array values
mat->mat[i][j] = array[i][j];
}
}
}
void matrix_wipe(Matrix *mat) {
for(int i = 0; i < mat->nrow; i++) {
free(mat->mat[i]);
}
free(mat->mat);
}
int main(void) {
Matrix temp;
double array[1][1];
array[0][0] = 34;
matrix_initializeFromArray(&temp, 1, 1, array);
matrix_wipe(&temp);
return 0;
}