How to free 2d array in C?

Question

I have the following code:

int **ptr = (int **)malloc(sizeof(int*)*N);  for(int i=0;i<N;i++)       ptr[i]=(int*)malloc(sizeof(int)*N)); 

How can I free ptr using free? Should I loop over ptr and free ptr[i] or should I just do

free(ptr)  

and ptr will be freed?

Answer 1

Just the opposite of allocation:

for(int i = 0; i < N; i++)     free(ptr[i]); free(ptr); 

Answer 2

You will have to loop over ptr[i], freeing each int* that you traverse, as you first suggest. For example:

for (int i = 0; i < N; i++) {     int* currentIntPtr = ptr[i];     free(currentIntPtr); }