socket编程：send()函数的使用和本质_winsock_api_linkage int wsaapi send怎么调用

1. 函数原型

发送功能在连接的套接字上发送数据。

int WSAAPI send(
  SOCKET     s,
  const char *buf,
  int        len,
  int        flags
);
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2. 作用

• 向目标发送数据
• 本质
  • send函数将我们的数据复制黏贴进系统的协议发送缓冲区，计算机伺机发送出去
  • 最大传输单元是1500字节

3. 函数使用

#ifndef UNICODE
#define UNICODE
#endif

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <Ws2tcpip.h>
#include <stdio.h>

// Link with ws2_32.lib
#pragma comment(lib, "Ws2_32.lib")

#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT 27015

int main() {

    //----------------------
    // Declare and initialize variables.
    int iResult;
    WSADATA wsaData;

    SOCKET ConnectSocket = INVALID_SOCKET;
    struct sockaddr_in clientService; 

    int recvbuflen = DEFAULT_BUFLEN;
    char *sendbuf = "Client: sending data test";
    char recvbuf[DEFAULT_BUFLEN] = "";

    //----------------------
    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != NO_ERROR) {
        wprintf(L"WSAStartup failed with error: %d\n", iResult);
        return 1;
    }

    //----------------------
    // Create a SOCKET for connecting to server
    ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (ConnectSocket == INVALID_SOCKET) {
        wprintf(L"socket failed with error: %ld\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    //----------------------
    // The sockaddr_in structure specifies the address family,
    // IP address, and port of the server to be connected to.
    clientService.sin_family = AF_INET;
    clientService.sin_addr.s_addr = inet_addr( "127.0.0.1" );
    clientService.sin_port = htons( DEFAULT_PORT );

    //----------------------
    // Connect to server.
    iResult = connect( ConnectSocket, (SOCKADDR*) &clientService, sizeof(clientService) );
    if (iResult == SOCKET_ERROR) {
        wprintf(L"connect failed with error: %d\n", WSAGetLastError() );
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
  }

    //----------------------
    // Send an initial buffer
    iResult = send( ConnectSocket, sendbuf, (int)strlen(sendbuf), 0 );
    if (iResult == SOCKET_ERROR) {
        wprintf(L"send failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    printf("Bytes Sent: %d\n", iResult);

    // shutdown the connection since no more data will be sent
    iResult = shutdown(ConnectSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        wprintf(L"shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    // Receive until the peer closes the connection
    do {

        iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
        if ( iResult > 0 )
            wprintf(L"Bytes received: %d\n", iResult);
        else if ( iResult == 0 )
            wprintf(L"Connection closed\n");
        else
            wprintf(L"recv failed with error: %d\n", WSAGetLastError());

    } while( iResult > 0 );


    // close the socket
    iResult = closesocket(ConnectSocket);
    if (iResult == SOCKET_ERROR) {
        wprintf(L"close failed with error: %d\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    WSACleanup();
    return 0;
}
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4. 函数参数

• 参数1：s
  • 标识已连接套接字的描述符。
• 参数2：buf
  • 指向包含要传输的数据的缓冲区的指针。
• 参数3：len
  • buf参数指向的缓冲区中数据的长度（以字节为单位）。
• 参数4：flags（一般写0）
  • 一组标志，指定进行呼叫的方式。 通过将按位或运算符与以下任何值一起使用来构造此参数。
  • MSG_DONTROUTE:指定不应对数据进行路由。 Windows套接字服务提供者可以选择忽略此标志。
  • MSG_OOB:发送OOB数据（仅SOCK_STREAM之类的流式套接字。

5. 返回值

• 成功返回写入的字节数
• 执行失败，返回SOCKET_ERROR