#include <stdio.h>#include <stdlib.h>#ifndef EXIT_FAILURE#  define EXIT_FAILURE	1#  define EXIT_SUCCESS	0#endif#include <limits.h>#ifndef PATH_MAX#  define PATH_MAX 255#endif#include <dlfcn.h>/* This is missing from very old Linux libc. */#ifndef RTLD_NOW#  define RTLD_NOW 2#endiftypedef int entrypoint (const char *argument);/* Save and return a copy of the dlerror() error  message,   since the next API call may overwrite the original. */static char *dlerrordup (char *errormsg);intmain (int argc, const char *argv[]){  const char modulepath[1+ PATH_MAX];  const char *errormsg = NULL;  void *module = NULL;  entrypoint *run = NULL;  int errors = 0;  if (argc != 3)    {      fprintf (stderr, "USAGE: main MODULENAME ARGUMENT\n");      exit (EXIT_FAILURE);    }  /* Set the module search path. */  getcwd (modulepath, PATH_MAX);  strcat (modulepath, "/");  strcat (modulepath, argv[1]);    /* Load the module. */  module = dlopen (modulepath, RTLD_NOW);  if (!module)    {      strcat (modulepath, ".so");      module = dlopen (modulepath, RTLD_NOW);    }  if (!module)    errors = 1;  /* Find the entry point. */  if (!errors)    {      run = dlsym (module, "run");      /* In principle, run might legitimately be NULL, so	 I don't use `run == NULL' as an error indicator. */      errormsg = dlerrordup (errormsg);      if (errormsg != NULL)	errors = dlclose (module);    }  /* Call the entry point function. */  if (!errors)    {      int result = (*run) (argv[2]);      if (result < 0)	errormsg = strdup ("module entry point execution failed");      else	printf ("\t=> %d\n", result);    }  /* Unload the module, now that we are done with it. */  if (!errors)    errors = dlclose (module);  if (errors)    {      /* Diagnose the encountered error. */      errormsg = dlerrordup (errormsg);      if (!errormsg)	{	  fprintf (stderr, "%s: dlerror() failed.\n", argv[0]);	  return EXIT_FAILURE;	}    }    if (errormsg)    {      fprintf (stderr, "%s: %s.\n", argv[0], errormsg);      free (errormsg);      return EXIT_FAILURE;    }    return EXIT_SUCCESS;}/* Be careful to save a copy of the error message,   since the next API call may overwrite the original. */static char *dlerrordup (char *errormsg){  char *error = (char *) dlerror ();  if (error && !errormsg)    errormsg = strdup (error);  return errormsg;}