判断文件是否存在

int access(const char* szPathName)

{

                                   #ifdef _WIN32

                                   if ( _access(szPathName, 0) != 0 )

                                          return -1;

                                   #else

                                   if ( access(szPathName, F_OK) != 0 )

                                          return -1;

                                   #endif

                                   return 0;

}