free_sized

Defined in header `<stdlib.h>`
void free_sized( void* ptr, size_t size );		(since C23)

Deallocates the space previously allocated by malloc(), calloc(), or realloc() (but not aligned_alloc()).

free_sized is thread-safe: it behaves as though only accessing the memory locations visible through its argument, and not any static storage.

A call to free_sized that deallocates a region of memory synchronizes-with a call to any subsequent allocation function that allocates the same or a part of the same region of memory. This synchronization occurs after any access to the memory by the deallocating function and before any access to the memory by the allocation function. There is a single total order of all allocation and deallocation functions operating on each particular region of memory.

Parameters

ptr	-	pointer to the memory to deallocate
size	-	size of memory previously passed to an allocation function

Return value

(none)

Notes

Possible implementation

void free_sized(void* ptr, size_t /*size*/)
{
    free(ptr);
}

Example

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>

typedef struct
{
    size_t size;     // current number of elements
    size_t capacity; // reserved number of elements
    void** data;
} PtrVector;

PtrVector vector_create(size_t initial_capacity)
{
    PtrVector ret =
    {
        .capacity = initial_capacity,
        .data = (void**) malloc(initial_capacity * sizeof(void*))
    };
    return ret;
}

void vector_delete(PtrVector* self)
{
    free_sized(self->data, self->capacity * sizeof(void*));
}

void vector_push_back(PtrVector* self, void* value)
{
    if (self->size == self->capacity)
    {
        self->capacity *= 2;
        self->data = (void**) realloc(self->data, self->capacity * sizeof(void*));
    }
    self->data[self->size++] = value;
}

int main()
{
    int data = 42;
    float pi = 3.141592f;
    PtrVector v = vector_create(8);
    vector_push_back(&v, &data);
    vector_push_back(&v, &pi);
    printf("data[0] = %i\n", *(int*)v.data[0]);
    printf("data[1] = %f\n", *(float*)v.data[1]);
    vector_delete(&v);
}

Output:

data[0] = 42
data[1] = 3.141592

References

C23 standard (ISO/IEC 9899:2024):

7.24.3.4 The free_sized function (p: 365-366)

free	deallocates previously allocated memory (function)
free_aligned_sized (C23)	deallocates previously allocated sized and aligned memory (function)
malloc	allocates memory (function)