Using realloc on a 2D array c

Question

I\'m kinda new to C sorry if my questions is somewhat vague;

I need to use realloc on a 2D array without losing it\'s previous data, I have this function in my progr

Answer 1

On success, realloc frees the pointer you pass to it and returns a pointer to the newly allocated memory. You're getting "junk values" because dereferencing a pointer to freed memory is undefined behavior.

It's not pretty, but the way to fix this (as another answer pointed out) is to pass a triple pointer (int***). That way the function can modify the original value of the pointer. This is how you simulate reference semantics in C, which is a strictly "pass by value" language.

void modifyMatrix(int ***iMat, int iRow, int iRow2, int iCol)
{
    int i;
    int **newMatrix = realloc(*iMat, iRow2 * sizeof(int*));
    if (newMatrix == NULL) {
           /* handle realloc error here */
    }
    else {
          *iMat = newMatrix; /* assign pointer to the new memory */
    }

    for(i=iRow; i

You've also got to add some error checking. If realloc fails and returns a NULL pointer, you've just created a memory leak: you no longer have the previous value of the pointer.

Note that I removed all of your casts. It's bad practice to cast the return of malloc and friends in C.