C error: undefined reference to

Question

I have created the following socket server in C (Windows) making use of the library Winsock.

#undef UNICODE

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <stdlib.h>

// Need to link with Ws2_32.lib
#pragma comment(lib, "WS2_32.lib")

#define DEFAULT_PORT "27015"
#define DEFAULT_BUFLEN 512

int __cdecl main(void) {

WSADATA wsaData;
int iResult;

SOCKET ListenSocket = INVALID_SOCKET;
SOCKET ClientSocket = INVALID_SOCKET;

struct addrinfo *result = NULL; 
struct addrinfo hints;

char recvbuf[DEFAULT_BUFLEN];
int iSendResult;
int recvbuflen = DEFAULT_BUFLEN;

// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if(iResult != 0) {
    printf("WSAStartup failed: %d\n", iResult);
    return 1;
}

ZeroMemory(&hints, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
hints.ai_flags = AI_PASSIVE;

// Resolve the local address and port to be used by the server
iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
if(iResult != 0) {
    printf("getaddrinfo failed: %d\n", iResult);
    WSACleanup();
    return 1;
}

// Create a SOCKET for the server to listen for client connections
ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
if(ListenSocket == INVALID_SOCKET) {
    printf("Error at socket(): %ld\n",  WSAGetLastError());
    freeaddrinfo(result);
    WSACleanup();
    return 1;
}

// Set up a TCP listening socket
iResult = bind(ListenSocket, result->ai_addr, (int)result->ai_addrlen);
if (iResult == SOCKET_ERROR) {
    printf("bind failed with error: %d\n", WSAGetLastError());
    freeaddrinfo(result);
    closesocket(ListenSocket);
    WSACleanup();
    return 1;
}
freeaddrinfo(result), // to free the memory allocated by getaddrinfo function

// Listen on a socket
iResult = listen(ListenSocket, SOMAXCONN);
if(iResult == SOCKET_ERROR) { // SOMAXCONN indicates the backlog value, maximum length of the queue of pending connections to accept
    printf("Listen failed with error: %d\n", WSAGetLastError());
    closesocket(ListenSocket);
    WSACleanup();
    return 1;
}

// Accept connection on a socket
ClientSocket = accept(ListenSocket, NULL, NULL);
if(ClientSocket == INVALID_SOCKET) {
    printf("accept failed: %d\n", WSAGetLastError());
    closesocket(ListenSocket);
    WSACleanup();
    return 1;
}
closesocket(ListenSocket); // No longer need server socket

// Receive until the peer shuts down the connection
do {
    iResult = recv(ClientSocket, recvbuf, recvbuflen, 0);
    if(iResult > 0) {
        printf("Bytes received: %d\n", iResult);

        // Echo buffer back to the sender
        iSendResult = send(ClientSocket, recvbuf, iResult, 0);
        if(iSendResult == SOCKET_ERROR) {
            printf("send failed: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        printf("Bytes sent: %d\n", iSendResult);
    } else if(iResult == 0) {
        printf("Connection closing...\n");
    } else {
        printf("recv failed: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }
} while(iResult > 0);

// Shutdown the send half of the connection since no more data will be sent
iResult = shutdown(ClientSocket, SD_SEND);
if(iResult == SOCKET_ERROR) {
    printf("shutdown failed: %d\n", WSAGetLastError());
    closessocket(ClientSocket);
    WSACleanup();
    return 1;
}

//cleanup
closesocket(ClientSocket);
WSACleanup();

return 0;
}

And when I try to compile it I get the following error for every function from the Winsock library:

C:\Users\Victor\AppData\Local\Temp\ccOwFjRF.o:socketServer.c:(.text+0x4a): undef
ined reference to `WSAStartup@8'

I added the directory where the Winsock library is to the path but it seems that I need to do something else. Does anyone have any idea about the problem? Thanks.

Answer 1

In order to get the compilation successful, you would require to perform the following changes:

1. In your source file, you would have to define #define _WIN32_WINNT 0x0501 before the inclusion of headers. Please refer to this earlier post for more details.

2. There is a typo in the sources. Please replace closessocket to closesocket at line no. 121 of your source file.

3. Compile with the following command

   gcc -o socketServer socketServer.c -lws2_32 -lwsock32 -L $MinGW\lib

Where $MinGW is the installation directory of MinGW softare

With these changes, I am able to compile your code successfully.