Unresolved external symbol LNK2019

Question

First of all, I know this question is all over this site but I have looked at almost all of them and can't seem to find out what is wrong. This is in VS 2012. Thanks.

//Socket.h #pragma once  #include <iostream> #include <WinSock2.h>  using namespace std;  const int STRLEN = 256;  class Socket {     protected:         WSADATA wsaData;         SOCKET mySocket;         SOCKET myBackup;         SOCKET acceptSocket;         sockaddr_in myAddress;     public:         Socket();         ~Socket();         bool SendData( char* );         bool RecvData( char*, int );         void CloseConnection();         void GetAndSendMessage(); };  class ServerSocket : public Socket {     public:         void Listen();         void Bind( int port );         void StartHosting( int port ); };  class ClientSocket : public Socket {     public:         void ConnectToServer( const char *ipAddress, int port ); }; 

Here's Socket.cpp

//Socket.cpp   #include "stdafx.h" #include "Socket.h"   Socket::Socket() {     if( WSAStartup( MAKEWORD(2, 2), &wsaData ) != NO_ERROR )     {         cerr<<"Socket Initialization: Error with WSAStartup\n";         system("pause");         WSACleanup();         exit(10);     }      //Create a socket     mySocket = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP );      if ( mySocket == INVALID_SOCKET )     {         cerr<<"Socket Initialization: Error creating socket"<<endl;         system("pause");         WSACleanup();         exit(11);     }      myBackup = mySocket; }  Socket::~Socket() {     WSACleanup(); }  bool Socket::SendData( char *buffer ) {     send( mySocket, buffer, strlen( buffer ), 0 );     return true; }  bool Socket::RecvData( char *buffer, int size ) {     int i = recv( mySocket, buffer, size, 0 );     buffer[i] = '\0';     return true; }  void Socket::CloseConnection() {     //cout<<"CLOSE CONNECTION"<<endl;     closesocket( mySocket );     mySocket = myBackup; }  void Socket::GetAndSendMessage() {     char message[STRLEN];     cin.ignore();//without this, it gets the return char from the last cin and ignores the following one!     cout<<"Send > ";     cin.get( message, STRLEN );     SendData( message ); }  void ServerSocket::StartHosting( int port ) {      Bind( port );      Listen(); }  void ServerSocket::Listen() {     //cout<<"LISTEN FOR CLIENT..."<<endl;      if ( listen ( mySocket, 1 ) == SOCKET_ERROR )     {         cerr<<"ServerSocket: Error listening on socket\n";         system("pause");         WSACleanup();         exit(15);     }      //cout<<"ACCEPT CONNECTION..."<<endl;      acceptSocket = accept( myBackup, NULL, NULL );     while ( acceptSocket == SOCKET_ERROR )     {         acceptSocket = accept( myBackup, NULL, NULL );     }     mySocket = acceptSocket; }  void ServerSocket::Bind( int port ) {     myAddress.sin_family = AF_INET;     myAddress.sin_addr.s_addr = inet_addr( "0.0.0.0" );     myAddress.sin_port = htons( port );      //cout<<"BIND TO PORT "<<port<<endl;      if ( bind ( mySocket, (SOCKADDR*) &myAddress, sizeof( myAddress) ) == SOCKET_ERROR )     {         cerr<<"ServerSocket: Failed to connect\n";         system("pause");         WSACleanup();         exit(14);     } }  void ClientSocket::ConnectToServer( const char *ipAddress, int port ) {     myAddress.sin_family = AF_INET;     myAddress.sin_addr.s_addr = inet_addr( ipAddress );     myAddress.sin_port = htons( port );      //cout<<"CONNECTED"<<endl;      if ( connect( mySocket, (SOCKADDR*) &myAddress, sizeof( myAddress ) ) == SOCKET_ERROR )     {         cerr<<"ClientSocket: Failed to connect\n";         system("pause");         WSACleanup();         exit(13);     }   } 

And here's stdafx.h

#pragma once  #include "targetver.h"  #define WIN32_LEAN_AND_MEAN             // Exclude rarely-used stuff from Windows headers // Windows Header Files: #include <windows.h>  // C RunTime Header Files #include <stdlib.h> #include <malloc.h> #include <memory.h> #include <tchar.h>   // TODO: reference additional headers your program requires here #include "Socket.h" 

And here are my error messages:

1>------ Build started: Project: Client, Configuration: Debug Win32 ------ 1>  stdafx.cpp 1>  Socket.cpp 1>  Client.cpp 1>  Generating Code... 1>Socket.obj : error LNK2019: unresolved external symbol __imp__accept@12 referenced in function "public: void __thiscall ServerSocket::Listen(void)" (?Listen@ServerSocket@@QAEXXZ) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__bind@12 referenced in function "public: void __thiscall ServerSocket::Bind(int)" (?Bind@ServerSocket@@QAEXH@Z) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__closesocket@4 referenced in function "public: void __thiscall Socket::CloseConnection(void)" (?CloseConnection@Socket@@QAEXXZ) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__connect@12 referenced in function "public: void __thiscall ClientSocket::ConnectToServer(char const *,int)" (?ConnectToServer@ClientSocket@@QAEXPBDH@Z) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__htons@4 referenced in function "public: void __thiscall ServerSocket::Bind(int)" (?Bind@ServerSocket@@QAEXH@Z) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__inet_addr@4 referenced in function "public: void __thiscall ServerSocket::Bind(int)" (?Bind@ServerSocket@@QAEXH@Z) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__listen@8 referenced in function "public: void __thiscall ServerSocket::Listen(void)" (?Listen@ServerSocket@@QAEXXZ) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__recv@16 referenced in function "public: bool __thiscall Socket::RecvData(char *,int)" (?RecvData@Socket@@QAE_NPADH@Z) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__send@16 referenced in function "public: bool __thiscall Socket::SendData(char *)" (?SendData@Socket@@QAE_NPAD@Z) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__socket@12 referenced in function "public: __thiscall Socket::Socket(void)" (??0Socket@@QAE@XZ) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__WSAStartup@8 referenced in function "public: __thiscall Socket::Socket(void)" (??0Socket@@QAE@XZ) 1>Socket.obj : error LNK2019: unresolved external symbol __imp__WSACleanup@0 referenced in function "public: __thiscall Socket::Socket(void)" (??0Socket@@QAE@XZ) 1>C:\Users\ajayp_000\documents\visual studio 2012\Projects\Client\Debug\Client.exe : fatal error LNK1120: 12 unresolved externals ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== 

Answer 1

The problem is you are not linking against the Ws2_32.lib library. To fix this you can add that to your additional dependencies tab of linker/Input settings for your project. Alternatively (as pointed out by SChepurin in the comments) you can add

#pragma comment(lib, "Ws2_32.lib") 

to a source file of your project.