Flexible Array Members in C

A flexible array member is an unsized array declared as the last member of a struct to support contiguous variable-length payload allocation.

• sizeof returns the size of the struct excluding the Flexible Array Member. Hence the need to add size * sizeof(type) in dynamic allocation.
• The Flexible Array has to be the last member of the struct.
• The Flexible Array can't be the only member of the struct.

#include <stdlib.h>

struct S {
    int size;
    int array[];
};

int main(void) {
    int size = 5;
    struct S* s;
    s = malloc(sizeof(struct S) + size * sizeof(int));

    return 0;
}

sizeof returns the size of struct S excluding the Flexible Array Member. Hence the need to add size * sizeof(int) in malloc. The Flexible Array has to be the last member of the struct. The Flexible Array can't be the only member of the struct.