PHP7：当我从变量中分配一个长度为字符串的字符串时，内存泄漏了吗？

Question

当我从常量int或size_t变量中分配长度的字符串时，它会让我感到困惑。它会造成内存泄漏。

另一方面，当我用数字分配时，它运行良好。发生了什么事？

    PHP_FUNCTION(aa_encrypt64) {
    const char *key = "";  // base64
    char *str = NULL;
    char *datetime = NULL;
    char *private_key = NULL;

    const size_t rtn_len = 32;       
    char rtn[rtn_len];           // char rtn[rtn_len]  leaves memory leak

    int argc = ZEND_NUM_ARGS();
    size_t str_len;
    size_t datetime_len;
    size_t private_key_len;

    if (zend_parse_parameters(argc, "sss", &str, &str_len, &datetime, &datetime_len, &private_key, &private_key_len) == FAILURE) 
        return;
        md5(str, rtn);
    RETURN_STRINGL(rtn, rtn_len);
}
PHP_FUNCTION(aa_decrypt64)
{

内存泄漏.....

   PHP_FUNCTION(aa_encrypt64) {
  const char *key = "";  // base64
  char *str = NULL;
  char *datetime = NULL;
  char *private_key = NULL;

  const size_t rtn_len = 32;       
  char rtn[32];           // char rtn[rtn_len]  leaves memory leak

  int argc = ZEND_NUM_ARGS();
  size_t str_len;
  size_t datetime_len;
  size_t private_key_len;

  if (zend_parse_parameters(argc, "sss", &str, &str_len, &datetime, &datetime_len, &private_key, &private_key_len) == FAILURE) 
    return;
  md5(str, rtn);
  RETURN_STRINGL(rtn, rtn_len);

}