WSASTARTUP()

this function is used to initialize the Winsock library, which provides the API for socket programming in Windows. This function must be called before using any socket-related functions such as socket(), bind(), connect(), etc. It sets up the internal data structures and loads the appropriate version of the Winsock DLL for network communication.

#include <stdio.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")
 
int main() 
{
  WSADATA d;
 
  // Initialize Winsock version 2.2
  if (WSAStartup(MAKEWORD(2, 2), &d)) {
    printf("Failed to initialize.\n");
    return -1;
  }
 
  WSACleanup();
  printf("Ok.\n");
  return 0;
}

 * the WSADATA structure will be filled in by WSAStartup() with details about the 
   Windows Sockets implementation. The WSAStartup() function returns 0 upon success, 
   and non-zero upon failure.
   
 * for Visual Studio the #pragma comment(lib, "ws2_32.lib") tells Microsoft Visual C to 
   link the executable with the Winsock library, ws2_32.lib.
    - this is ignored on MinGW
       - to explicitly tell the MinGW compiler to link in the library, add the
         cmdline option, -lws2_32.
          - gcc win_init.c -o win_init.exe -lws2_32