How does free know how much to free?

Question

In C programming, you can pass any kind of pointer you like as an argument to free, how does it know the size of the allocated memory to free? Whenever I pass a pointer to s

Answer 1

To answer the second half of your question: yes, you can, and a fairly common pattern in C is the following:

typedef struct {
    size_t numElements
    int elements[1]; /* but enough space malloced for numElements at runtime */
} IntArray_t;

#define SIZE 10
IntArray_t* myArray = malloc(sizeof(intArray_t) + SIZE * sizeof(int));
myArray->numElements = SIZE;