vla.c

/* # VLA
 *
 * # Variable length array
 *
 * Implementation:
 *
 * - increase/decrease stack pointer
 * - requires one addition and one multiplication per declaration
 *
 * Pros and cons:
 *
 * - http://stackoverflow.com/questions/2034712/is-there-any-overhead-for-using-variable-length-arrays
 * - http://stackoverflow.com/questions/16672322/malloced-array-vs-variable-length-array
 */

#include "common.h"

#if __STDC_VERSION__ >= 199901L
/* # [*]
 *
 *  The "[*]" declaration syntax is possible to avoid naming parameters.
 */
void vla_arg(size_t, int vla[*]);
void vla_arg(size_t size, int vla[size]) {}

void vla_arg_k_and_r(size, vla)
/*int vla[size];*/ /* ERROR: must come after. */
size_t size;
int vla[size];
{}
#endif

int main(void) {
#if __STDC_VERSION__ >= 199901L
    {
        srand(time(NULL));
        int size = 1 + (rand() % 10);
        int vla[size];

        /* sizeof is evaluated at runtime for VLAs */
        assert(sizeof(vla) == size * sizeof(int));
    }

    /* VLAs can be passed to functions.
     *
     * http://stackoverflow.com/questions/17371645/parameter-of-a-function
     */
    {
        size_t size = 2;
        int vla[size];
        vla_arg(size, vla);
    }

    /* If the size must come after the vla (for example, to interface witha FORTRAN
     * interface that does so), the only possibility is to use K&R function definition syntax!
     *
     * This is one of the very few application of K&R syntax to C99.
     */
    {
        size_t size = 2;
        int vla[size];
        vla_arg_k_and_r(vla, size);
    }

    /* Initialize VLA: nope:
     * http://stackoverflow.com/questions/17332360/initializing-variable-length-array
     */
#endif
    return EXIT_SUCCESS;
}