static unsigned char db[] = { 0xDE, 0xAD, 0xBE, 0xEF };
static unsigned char buff[SOME_RANDOM_LENGTH];

int main()
{
    int n = sizeof buff / sizeof db;
    unsigned char *ptr = buff;

    for ( ; n ; n--, ptr+=4 ) {
        memcpy( ptr, db, 4 );
    }

    switch ( sizeof buff % sizeof db ) {
    case 3:
        ptr[2] = db[2];
    case 2:
        ptr[1] = db[1];
    case 1:
        ptr[0] = db[0];
        break;
    }

    return 0;
}