Avoid using `mrb_str_to_cstr` if possible

Because it always allocate new string. Replace with the followings:

- Use `RSRING_PTR` if string is guaranteed to be null-terminated.
- Use `mrb_string_value_cstr` or `mrb_get_args("z")` if return value isn't
  modified.

1 files changed, 2 insertions, 4 deletions

diff --git a/mrbgems/mruby-io/test/mruby_io_test.c b/mrbgems/mruby-io/test/mruby_io_test.c
index 71239a827..3312d6c7e 100644
--- a/mrbgems/mruby-io/test/mruby_io_test.c
+++ b/mrbgems/mruby-io/test/mruby_io_test.c
@@ -215,11 +215,9 @@ mrb_io_test_mkdtemp(mrb_state *mrb, mrb_value klass)
 static mrb_value
 mrb_io_test_rmdir(mrb_state *mrb, mrb_value klass)
 {
-  mrb_value str;
-  char *cp;
+  const char *cp;
 
-  mrb_get_args(mrb, "S", &str);
-  cp = mrb_str_to_cstr(mrb, str);
+  mrb_get_args(mrb, "z", &cp);
   if (rmdir(cp) == -1) {
     mrb_sys_fail(mrb, "rmdir");
   }