Memory leak lefts when I allocate a string with the length from a variable?

[Deleted user]

It confuses me when I allocate a string with the length from a constant int or size_t variable. It'll make memory leak.

On the other hand, it works well when I allocate it with a number. What's going on with it?

`

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)
{

`
Memory leaks .....

`

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

  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);
 }

`
Fine...