#if __FreeBSD__ == 0            /* 1.0 did not define __FreeBSD__ */
#define __FreeBSD_version 199401
#elif __FreeBSD__ == 1          /* 1.1 defined it to be 1 */
#define __FreeBSD_version 199405
#else                           /* 2.0 and higher define it to be 2 */
#include <osreldate.h>          /* and this works */
#endif
#include <stdio.h>
#include <unistd.h>

int
main(void) {
        printf("Compilation release date: %d\n", __FreeBSD_version);
#if __FreeBSD_version >= 199408
        printf("Execution environment release date: %d\n", getosreldate());
#else
        printf("Execution environment release date: can't tell\n");
#endif
        return (0);
}