gcc -o myProgramName myProgramName.o -ldllName

gcc -o myProgramName myProgramName.o -L/path/to/my/library/folder -ldllName

LD_LIBRARY_PATH=path/to/my/library/folder -ldllName

...
#include "dllName.h"
int main()
{
   ...
   // some code
   ...
}

// далі, як згадано вище - gcc ... -ldllName

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
int main(int argc, char **argv)
{
    void *handle;
    double (*cosine)(double);
    char *error;
    handle = dlopen ("libm.so", RTLD_LAZY);
    if (!handle) 
    {
        fprintf (stderr, "%s\n", dlerror());
        exit(1);
    }
    dlerror();    /* Clear any existing error */
    cosine = dlsym(handle, "cos");
    if ((error = dlerror()) != NULL)  
    {
        fprintf (stderr, "%s\n", error);
        exit(1);
    }
    printf ("%f\n", (*cosine)(2.0));
    dlclose(handle);
    return 0;
}

                                                                                ^
yoba_parser.cpp:46:23: error: ‘NET_DVR_Init’ was not declared in this scope
     if( !NET_DVR_Init() )
                       ^
yoba_parser.cpp:51:28: error: ‘NET_DVR_SetConnectTime’ was not declared in this scope
     NET_DVR_SetConnectTime();
                            ^
yoba_parser.cpp:52:26: error: ‘NET_DVR_SetReconnect’ was not declared in this scope
     NET_DVR_SetReconnect();
                          ^
yoba_parser.cpp:54:5: error: ‘NET_DVR_DEVICEINFO’ was not declared in this scope
     NET_DVR_DEVICEINFO device_info;
     ^
yoba_parser.cpp:54:24: error: expected ‘;’ before ‘device_info’
     NET_DVR_DEVICEINFO device_info;
                        ^
yoba_parser.cpp:56:9: error: expected ‘;’ before ‘ip’
  file_t ip( fopen( ip_file.val, "r" ), &fclose );
         ^
yoba_parser.cpp:59:43: error: ‘ip’ was not declared in this scope
     while( fgets( buffer, sizeof(buffer), ip.get() ) )
                                           ^
yoba_parser.cpp:62:83: error: ‘device_info’ was not declared in this scope
   UserID = NET_DVR_Login( buffer, atoi( port_num.val ), login.val, password.val, &device_info );
                                                                                   ^
yoba_parser.cpp:62:95: error: ‘NET_DVR_Login’ was not declared in this scope
   UserID = NET_DVR_Login( buffer, atoi( port_num.val ), login.val, password.val, &device_info );
                                                                                               ^
yoba_parser.cpp:69:27: error: ‘NET_DVR_Logout’ was not declared in this scope
    NET_DVR_Logout( UserID );
                           ^
yoba_parser.cpp:72:2: error: ‘ip’ was not declared in this scope
  ip.reset();
  ^
yoba_parser.cpp:73:21: error: ‘NET_DVR_Cleanup’ was not declared in this scope
     NET_DVR_Cleanup();
                     ^
yoba_parser.cpp: In function ‘void WriteData(const char*, ...)’:
yoba_parser.cpp:81:2: error: ‘file_t’ was not declared in this scope
  file_t outputFile( fopen( out_file.val, "a" ), &fclose );
  ^
yoba_parser.cpp:81:9: error: expected ‘;’ before ‘outputFile’
  file_t outputFile( fopen( out_file.val, "a" ), &fclose );
         ^
yoba_parser.cpp:83:7: error: ‘outputFile’ was not declared in this scope
  if( !outputFile.get() )
       ^
yoba_parser.cpp:88:28: error: ‘va_start’ was not declared in this scope
     va_start( list, format );
                            ^
yoba_parser.cpp:89:15: error: ‘outputFile’ was not declared in this scope
     vfprintf( outputFile.get(), format, list );
               ^
yoba_parser.cpp:90:18: error: ‘va_end’ was not declared in this scope
     va_end( list );