dltest.c

linux 学习的课件

/*************************************************************/
/*     Test Linux Dynamic Function Loading              */
/*                                      */
/*     void       *dlopen(const char *filename, int flag)           */
/*          Opens dynamic library and return handle     */
/*                                      */
/*     const char *dlerror(void)                    */
/*          Returns string describing the last error.           */
/*                                      */
/*     void       *dlsym(void *handle, char *symbol)            */
/*          Return pointer to symbol's load point.          */
/*          If symbol is undefined, NULL is returned.           */
/*                                      */
/*     int        dlclose (void *handle)                    */
/*          Close the dynamic library handle.               */
/*                                      */
/*                                      */
/*                                      */
/*************************************************************/
#include<stdio.h>
#include    <stdlib.h>
 
/*                              */
/* 1-dll include file and variables */
/*                              */
#include    <dlfcn.h>

void  *FunctionLib;     /*  Handle to shared lib file   */
int   (*Function)();        /*  Pointer to loaded routine   */
const char *dlError;        /*  Pointer to error string     */


main( argc, argv )
{
  int   rc;             /*  return codes            */
  char HelloMessage[] = "HeLlO WoRlD\n";
 
/*                              */
/* 2-print the original message                 */
/*                              */
  printf("  dlTest  2-Original message \n");
  printf("%s", HelloMessage);
/*                                               */
/*  3-Open Dynamic Loadable Libary with absolute path      */
/*                                              */
  FunctionLib = dlopen("/home/dlTest/UPPERCASE.so",RTLD_LAZY);
  dlError = dlerror();
  printf("  dlTest  3-Open Library with absolute path return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 4-Find the first loaded function */
/*                              */
  Function    = dlsym( FunctionLib, "printUPPERCASE");
  dlError = dlerror();
  printf("  dlTest  4-Find symbol printUPPERCASE return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 5-Execute the first loaded function              */
/*                              */
  rc = (*Function)( HelloMessage );
  printf("  dlTest  5-printUPPERCASE return-%s- \n", dlError);
/*                              */
/* 6-Close the shared library handle                    */
/* Note:  after the dlclose, "printUPPERCASE" is not loaded     */
/*                              */
  rc = dlclose(FunctionLib);
  dlError = dlerror();
  printf("  dlTest  6-Close handle return-%s-\n",dlError); 
  if( rc ) exit(1);
/*                              */
/*  7-Open Dynamic Loadable Libary using LD_LIBRARY path        */
/*                              */
  FunctionLib = dlopen("lowercase.so",RTLD_LAZY);
  dlError = dlerror();
  printf("  dlTest  7-Open Library with relative path return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 8-Find the second loaded function                */
/*                              */
  Function    = dlsym( FunctionLib, "printLowercase");
  dlError = dlerror();
  printf("  dlTest  8-Find symbol printLowercase return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 8-execute the second loaded function             */
/*                              */
  rc = (*Function)( HelloMessage );
  printf("  dlTest  9-printLowercase return-%s- \n", dlError);
/*                              */
/* 10-Close the shared library handle               */
/*                              */
  rc = dlclose(FunctionLib);
  dlError = dlerror();
  printf("  dlTest 10-Close handle return-%s-\n",dlError); 
  if( rc ) exit(1);
  return(0);
}