int matrix with pointers in C - memory allocation confusion

Question

I\'m having some issues with producing an int matrix without creating memory leaks. I want to be able to make a given (global) matrix into any size dynamically via read_matr

Answer 1

Just because the memory has been free'd doesn't mean you can't access it! Of course, it's a very bad idea to access it after it's been free'd, but that's why it works in your example.

Note that free( *first_matrix ) only free's first_matrix[0], not the other arrays. You probably want some kind of marker to signify the last array (unless you will always know when you free the outer array how many inner arrays you allocated). Something like:

int** read_matrix(int size_x, int size_y)
{
    int** matrix;
    matrix = calloc(size_x, 1+sizeof(int*)); // alloc one extra ptr
    for(int i = 0;i

Then when you're freeing them:

// keep looping until you find the NULL one
for( int i=0; first_matrix[i] != NULL; i++ ) {
    free( first_matrix[i] );
}
free( first_matrix );