winSocket第一步WSAStartup

寫了很多socket了，很少關注socket的第一步

#define WIN32_LEAN_AND_MEAN

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

// Need to link with Ws2_32.lib
#pragma comment(lib, "ws2_32.lib")


int __cdecl main()
{

    WORD wVersionRequested;
    WSADATA wsaData;
    int err;

/* Use the MAKEWORD(lowbyte, highbyte) macro declared in Windef.h */
    wVersionRequested = MAKEWORD(2, 2);

    err = WSAStartup(wVersionRequested, &wsaData);
    if (err != 0) {
        /* Tell the user that we could not find a usable */
        /* Winsock DLL.                                  */
        printf("WSAStartup failed with error: %d\n", err);
        return 1;
    }

/* Confirm that the WinSock DLL supports 2.2.*/
/* Note that if the DLL supports versions greater    */
/* than 2.2 in addition to 2.2, it will still return */
/* 2.2 in wVersion since that is the version we      */
/* requested.                                        */

    if (LOBYTE(wsaData.wVersion) != 2 || HIBYTE(wsaData.wVersion) != 2) {
        /* Tell the user that we could not find a usable */
        /* WinSock DLL.                                  */
        printf("Could not find a usable version of Winsock.dll\n");
        WSACleanup();
        return 1;
    }
    else
        printf("The Winsock 2.2 dll was found okay\n");
        

/* The Winsock DLL is acceptable. Proceed to use it. */

/* Add network programming using Winsock here */

/* then call WSACleanup when done using the Winsock dll */
    
    WSACleanup();

}

其實這段代碼也不用過多關注。

從WSAStartup入手：

int WSAStartup(
  WORD      wVersionRequired,
  LPWSADATA lpWSAData
);

該 調用WSAStartup函數初始化了一個進程使用Winsock DLL的使用信息

第一個參數不用關注。

typedef struct WSAData {
  WORD           wVersion;
  WORD           wHighVersion;
} WSADATA;

該 WSADATA結構包含在Windows Sockets實現信息。其他字段只是爲了兼容版本。再socket2之後已經只有這兩個字段有意義了。就是制定soocket的版本號。

一旦應用程序或DLL成功進行了 WSAStartup調用，它就可以根據需要繼續進行其他Windows套接字調用。完成使用Winsock DLL的服務後，應用程序必須調用 WSACleanup，以允許Winsock DLL釋放應用程序使用的內部Winsock資源。

在每次成功調用WSAStartup函數時，應用程序都必須調用WSACleanup函數。舉例來說，這意味着如果一個應用程序調用 WSAStartup 3次，則它必須調用 WSACleanup 3次。對WSACleanup的前兩個調用 除了減少內部計數器外沒有任何作用。該任務的最後 WSACleanup調用完成了該任務的所有必要資源重新分配。