C++ Dll linking Curl - c++

Question

I am trying to create a dll which uses the curl library for a very simple function. Everything works just fine, the only problem is, that the curl linking does not seem to work properly.
I use the same linking, preprocessordefines and include directories like in my executable project where it works just fine so i am pretty sure it´s not about my linking or binary files of the libary.
Are there any special properties to link a libary to a dll?
My minimal sample code:
C++ Mainfile:
#include "main.h"
#include <Windows.h>
#include <curlpp/cURLpp.hpp>
#include <curlpp/Easy.hpp>
#include <curlpp/Info.hpp>
#include <curlpp/Options.hpp>
#include <curlpp/Exception.hpp>
namespace CurlDll
{
void CallHost::Try()
{
curlpp::Easy request;
request.setOpt(new curlpp::options::UserAgent("Mozilla/4.0"));
request.setOpt(new curlpp::options::AutoReferer(true));
request.setOpt(new curlpp::options::FollowLocation(true));
request.setOpt(new curlpp::options::Url("http://xml.utrace.de"));
request.perform();
MessageBox(0,"lololowwwwwwwwwwwl", "wqgqwwwwwgq", MB_OK |MB_ICONINFORMATION);
}
}
BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason)
{return 1;}
Header file:
#ifdef MAIN_EXPORTS
#define MAIN_API __declspec(dllexport)
#else
#define MAIN_API __declspec(dllimport)
#endif
#include <iostream>
namespace CurlDll
{
class CallHost
{
public:
static MAIN_API void Try();
};
}
i get following linking errors #drescherjm
(47 , i will just post a few, i think that shouls be enough)
ERROR 2 error LNK2001: unresolved external Symbol
"__imp__WSAStartup#8".
ERROR 11 error LNK2001: unresolved external Symbol
"__imp__WSAGetLastError#0".
ERROR 33 error LNK2001: unresolved external Symbol
"__imp__setsockopt#20".

Answer 1

The linker errors are telling you that the linker cannot find definitions for these functions: WSAStartup, WSAGetLastError, setsockopt. These functions are defined in the import library Ws2_32.lib. You need to supply that import library to the linker.
This information is given in the documentation for the functions. For instance, the documentation for WSAStartup. At the bottom of the documentation topic is a table listing requirements. Note the required library, Ws2_32.lib.

Answer 2

The symbols WSAStartup, WSAGetLastError and setsocketopt are part of the Windows API, in Ws2_32.lib (e.g. see http://msdn.microsoft.com/en-gb/library/windows/desktop/ms742213(v=vs.85).aspx )
You should include ws2_32.lib as an additional library when you link your DLL. If you're using Visual Studio, it's likely that the search path should already find it; just add it as an additional library.
So actually, I suspect you're not using the exact same linker options compared to your .exe
If you're building a .exe or a .dll, the linker needs to ensure it can resolve ALL known symbols at link time.