Core cannot handle null system directory

[geajack]

Libretro provides a "RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY" environment variable, which according to the comments in the code is intended to be optional:

#define RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY 9
                                           /* const char ** --
                                            * Returns the "system" directory of the frontend.
                                            * This directory can be used to store system specific
                                            * content such as BIOSes, configuration data, etc.
                                            * The returned value can be NULL.
                                            * If so, no such directory is defined,
                                            * and it's up to the implementation to find a suitable directory.
                                            *
                                            * NOTE: Some cores used this folder also for "save" data such as
                                            * memory cards, etc, for lack of a better place to put it.
                                            * This is now discouraged, and if possible, cores should try to
                                            * use the new GET_SAVE_DIRECTORY.
                                            */

However, code in this project crashes if the libretro frontend gives a value of NULL:

// libgambatte/libretro/libretro.cpp:73
bool file_present_in_system(std::string fname)
{
   const char *systemdirtmp = NULL;
   bool worked = environ_cb(RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY, &systemdirtmp);
   if (!worked)
      return false;

   std::string fullpath  = systemdirtmp;
   fullpath             += "/";
   fullpath             += fname;

   RFILE *fp             = filestream_open(fullpath.c_str(), RETRO_VFS_FILE_ACCESS_READ,
         RETRO_VFS_FILE_ACCESS_HINT_NONE);

   if (fp)
   {
      filestream_close(fp);
      return true;
   }

   return false;
}

The line at which fullpath is declared raises an exception and kills the app. I'm only just getting started with libretro, but this seems like non-compliance with the spec.

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[negativeExponent]

• RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY can't be NULL or false, since this will return CONTENT_DIR instead (probably depends on platform). (replaced with "default" in retroarch.cfg)

• file_present_in_system() is used to look for and load "gbc_bios.bin", which in this case will look for it in the roms folder. the "/" can probably be changed to what is usually used in the cores like so:

  #ifdef _WIN32
  static char slash = '\\';
  #else
  static char slash = '/';
  #endif

[inactive123]

I have been told by @jdgleaver this should be fine now, closing...