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本节通过一个Windows控制台应用程序实现基于流式套接字的回射功能。回射是指服务器接收客户发来的字符，并将接收到的内容再次发送回客户端，以检测网络和主机运行状态。本节设计客户和服务器两个独立的网络应用程序，结合网络操作的基本步骤讲述流式套接字编程中各函数的使用方法。
客户端程序接收命令行参数argv[1]传入的服务器端地址，与服务器进行连接。Visual Studio编译器设置命令行参数方法：项目（右键）属性——》调试——》命令参数。
客户端完整代码：
#define WIN32_LEAN_AND_MEAN#include#include #include #include #include #pragma comment (lib, "Ws2_32.lib")#pragma comment (lib, "Mswsock.lib")#pragma comment (lib, "AdvApi32.lib")#define DEFAULT_BUFLEN 512#define DEFAULT_PORT "27015"int __cdecl main(int argc, char **argv) { WSADATA wsaData; SOCKET ConnectSocket = INVALID_SOCKET; struct addrinfo *result = NULL, *ptr = NULL, hints; char sendbuf[] = "this is a test"; char recvbuf[DEFAULT_BUFLEN]; int iResult; int recvbuflen = DEFAULT_BUFLEN; if (argc != 2) { printf("usage: %s server-name\n", argv[0]); return 1; } iResult = WSAStartup(MAKEWORD(2, 2), &wsaData); if (iResult != 0) { printf("WSAStartup failed with error: %d\n", iResult); return 1; } ZeroMemory(&hints, sizeof(hints)); hints.ai_family = AF_UNSPEC; hints.ai_socktype = SOCK_STREAM; hints.ai_protocol = IPPROTO_TCP; iResult = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result); if (iResult != 0) { printf("getaddrinfo failed with error: %d\n", iResult); WSACleanup(); return 1; } for (ptr = result; ptr != NULL; ptr = ptr->ai_next) { ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype, ptr->ai_protocol); if (ConnectSocket == INVALID_SOCKET) { printf("socket failed with error: %ld\n", WSAGetLastError()); WSACleanup(); return 1; } iResult = connect(ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen); if (iResult == SOCKET_ERROR) { closesocket(ConnectSocket); ConnectSocket = INVALID_SOCKET; continue; } break; } freeaddrinfo(result); if (ConnectSocket == INVALID_SOCKET) { printf("Unable to connect to server!\n"); WSACleanup(); return 1; } iResult = send(ConnectSocket, sendbuf, (int)strlen(sendbuf), 0); if (iResult == SOCKET_ERROR) { printf("send failed with error: %d\n", WSAGetLastError()); closesocket(ConnectSocket); WSACleanup(); return 1; } printf("Bytes Sent: %ld\n", iResult); iResult = shutdown(ConnectSocket, SD_SEND); if (iResult == SOCKET_ERROR) { printf("shutdown failed with error: %d\n", WSAGetLastError()); closesocket(ConnectSocket); WSACleanup(); return 1; } do { iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0); if (iResult > 0) { printf("Bytes received: %d\n", iResult); } else if (iResult == 0) { printf("Connection closed\n"); } else { printf("recv failed with error: %d\n", WSAGetLastError()); closesocket(ConnectSocket); WSACleanup(); return 1; } } while (iResult > 0); closesocket(ConnectSocket); WSACleanup(); return 0;}
服务器端完整代码：
#undef UNICODE#define WIN32_LEAN_AND_MEAN#include#include #include #include #include #pragma comment (lib, "Ws2_32.lib")#define DEFAULT_BUFLEN 512#define DEFAULT_PORT "27015"int __cdecl main(void) { WSADATA wsaData; int iResult; SOCKET ListenSocket = INVALID_SOCKET; SOCKET ClientSocket = INVALID_SOCKET; struct addrinfo *result = NULL; struct addrinfo hints; int iSendResult; char recvbuf[DEFAULT_BUFLEN]; int recvbuflen = DEFAULT_BUFLEN; iResult = WSAStartup(MAKEWORD(2, 2), &wsaData); if (iResult != 0) { printf("WSAStartup failed with error: %d\n", iResult); return 1; } ZeroMemory(&hints, sizeof(hints)); hints.aifamily = AF_INET; hints.aisocktype = SOCK_STREAM; hints.aiprotocol = IPPROTO_TCP; hints.aiflags = AI_PASSIVE; iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result); if (iResult != 0) { printf("getaddrinfo failed with error: %d\n", iResult); WSACleanup(); return 1; } ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol); if (ListenSocket == INVALID_SOCKET) { printf("socket failed with error: %ld\n", WSAGetLastError()); freeaddrinfo(result); WSACleanup(); return 1; } 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); iResult = listen(ListenSocket, SOMAXCONN); if (iResult == SOCKET_ERROR) { printf("listen failed with error: %d\n", WSAGetLastError()); closesocket(ListenSocket); WSACleanup(); return 1; } ClientSocket = accept(ListenSocket, NULL, NULL); if (ClientSocket == INVALID_SOCKET) { printf("accept failed with error: %d\n", WSAGetLastError()); closesocket(ListenSocket); WSACleanup(); return 1; } closesocket(ListenSocket); do { iResult = recv(ClientSocket, recvbuf, recvbuflen, 0); if (iResult > 0) { printf("Bytes received: %d\n", iResult); iSendResult = send(ClientSocket, recvbuf, iResult, 0); if (iSendResult == SOCKET_ERROR) { printf("send failed with error: %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 with error: %d\n", WSAGetLastError()); closesocket(ClientSocket); WSACleanup(); return 1; } } while (iResult > 0); iResult = shutdown(ClientSocket, SD_SEND); if (iResult == SOCKET_ERROR) { printf("shutdown failed with error: %d\n", WSAGetLastError()); closesocket(ClientSocket); WSACleanup(); return 1; } closesocket(ClientSocket); WSACleanup(); return 0;}
运行环境：Visual Studio 2019，Windows 10专业版。
新建工程，并创建两个项目，分别用于编写服务器端和客户端的程序。将上述代码写入各自的.cpp文件中。
设置客户端命令行参数：鼠标右键cli项目——》属性，选择调试，在命令参数中输入服务器IP地址。由于是本地测试，这里使用本地环回地址127.0.0.1。
由于需要同时运行服务器和客户端两个程序，这里设置编译器为多项目启动方式。
右键解决方案——》属性，选择通用属性——》启动项目——》多个启动项目，将ser和cli都设置为启动。
在项目依赖项中选择cli项目依赖于ser。
点击运行，运行结果如图所示。
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