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前言

大多数项目都在Linux系列的操作系统下开发服务器端，而多数客户端是在Windows平台下开发的。不仅如此，有时应用程序还需要在两个平台之间相互切换。因此，学习套接字编程的过程中，有必要兼顾Windows和Linux两大平台。另外，这两大平台下的套接字编程非常类似，如果把其中相似的部分放在一起讲解，将大大提高学习效率。只要理解好其中一个平台下的网络编程方法，就很容易通过分析差异掌握另一平台。因为不论什么方式实现，底层的逻辑都是完全一致的。

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一、Windows环境下实现TCP通信

为了在Winsock基础上开发网络程序，需要做如下准备，以下两个文件都是系统自带的，包含时注意目标平台版本与库的版本一致。
导入头文件winsock2.h。
链接ws2_32.lib库（库名称和链接目录）。

1.服务器

#include <stdio.h>
#include <stdlib.h>
#include <WinSock2.h>

void ErrorHandling(char *message)
 {
	fputs(message, stderr);
	fputs("\n", stderr);
	exit(1);
}

int main(int argc, char * argv[])
 {
	WSADATA wsaData;
	SOCKET hServSock, hClntSock;
	SOCKADDR_IN servAddr, clntAddr;
	int szClntAddr;
	char message[] = "Hello World!";
	if (argc != 2) 
	{
		printf("Usage : %s <port>", argv[0]);
		exit(1);
	}

	if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0)
		ErrorHandling("WSAStartup() error!");

	hServSock = socket(PF_INET, SOCK_STREAM, 0);
	if (hServSock == INVALID_SOCKET)
		ErrorHandling("socket() error!");

	memset(&servAddr, 0, sizeof(servAddr));
	servAddr.sin_family = AF_INET;
	servAddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servAddr.sin_port = htons(atoi(argv[1]));

	if (bind(hServSock, (SOCKADDR *)&servAddr, sizeof(servAddr)) == SOCKET_ERROR)
		ErrorHandling("bind() error!");

	if (listen(hServSock, 5) == SOCKET_ERROR)
		ErrorHandling("listen() error!");

	szClntAddr = sizeof(clntAddr);
	hClntSock = accept(hServSock, (SOCKADDR*)&clntAddr, &szClntAddr);
	if (hClntSock == INVALID_SOCKET)
		ErrorHandling("accept() error!");
	fputs("sending message...", stderr);
	fputs("", stderr);
	send(hClntSock, message, sizeof(message), 0);
	closesocket(hClntSock);
	closesocket(hServSock);
	WSACleanup();
	return 0;
}

2.客户端

#include <stdio.h>
#include <stdlib.h>
#include <WinSock2.h>
void ErrorHandling(char* message);

int main(int argc, char *argv[]) 
{
	WSADATA wsaData;
	SOCKET hSocket;
	SOCKADDR_IN servAddr;

	char message[30];
	int strlen;
	if (argc != 3) 
	{
		printf("Usage: %s <IP> <port>", argv[0]);
	exit(1);
	}

	if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0)
		ErrorHandling("WSAStartup() error!");

	hSocket = socket(PF_INET, SOCK_STREAM, 0);
	if (hSocket == INVALID_SOCKET)
		ErrorHandling("socket() error!");

	memset(&servAddr, 0, sizeof(servAddr));
	servAddr.sin_family = AF_INET;
	servAddr.sin_addr.s_addr = inet_addr(argv[1]);
	servAddr.sin_port = htons(atoi(argv[2]));

	if (connect(hSocket, (SOCKADDR*)&servAddr, sizeof(servAddr)) == SOCKET_ERROR)
		ErrorHandling("connect() error!");

	strlen = recv(hSocket, message, sizeof(message) - 1, 0);
	if (strlen == -1)
		ErrorHandling("read() error!");

	printf("Message from server:%s", message);
	closesocket(hSocket);
	WSACleanup();
	return 0;
}

void ErrorHandling(char * message) {
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}

3.运行

运行时直接进入到可执行程序文件，使用命令行运行

C:\tcpip>tcp_win_server 9190

C:\tcpip>tcp_win_client 127.0.0.1 9190

二、Linux环境下实现TCP通信

1.服务端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
void error_handling(char *message);
int main(int argc,char *argv[])
{
	int serv sock;
	int clnt sock;
	struct sockaddr in serv addr;
	struct sockaddr in clnt addr;
	socklen t clnt addr size;
	char message[]="Hello World!";
	if(argc!=2)
	{
		printf("Usage :%s<port>\n",argv[0]);
		exit(1);
	}
	serv sock=Socket(PF INET,SOCK STREAM，0);
	if(serv sock ==-1)
		error_handling("socket() error");
	memset(&serv_addr,0,sizeof(serv addr));
	serv_addr.sin_family=AF INET;
	serv_addr.sin_addr.s addr=htonl(INADDR ANY);
	serv_addr.sin_port=htons(atoi(argv[1]));
	if(bind(serv_sock,(struct sockaddr*)&serv_addr, sizeof(serv_addr))==-1)
		error_handling("bind() error");
	if(listen(serv sock,5)==-1)
		error_handling("listen() error");
	clnt addr size=sizeof(clnt addr);
	cInt sock=accept(sery sock,(struct sockaddr*)&cInt addr,&cInt addr size);
	if(clnt sock==-1)
		error_handling("accept() error");
	write(clnt_sock,message,sizeof(message));
	close(clnt sock);
	close(serv sock);return 0;
}
void error handling(char *message)
{
	fputs(message, stderr);
	fputc('\n',stderr);
	exit(1);
}

2.客户端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
void error handling(char *message);
int main(int argc, char* argv[])
{
	int sock;
	struct sockaddr_in serv_addr;
	char message[30];
	int str_len;
	if(argc!-3)
	{
		printf("Usage :%s<IP><port>\n",argv[0]);
		exit(1);
	}
	sock=socket(PF INET,SOCK STREAM, 0);
	if(sock == -1)
		error_handling("socket() error")
	memset(&serv addr,0,sizeof(serv addr));
	serv addr.sin family=AF INET;
	serv addr.sin addr.s addr-inet addr(argv[1]);
	serv_addr.sin port=htons(atoi(argv[2]));
	if(connect(sock,(struct sockaddr*)&serv addr,sizeof(serv_addr))==-1)
		error_handling("connect() error!");
	str len=read(sock,message,sizeof(message)-1);
	if(str len=--1)
		error_handling("read()error!");
	printf("Message from server :Xs n",message);
	close(sock);
	return 0;
}
void error handling(char*message)
{
	fputs(message, stderr)fputc('\n',stderr);
	exit(1);
}

三、Qt实现TCP通信

相对于前边两种方法，QT进行了一定封装，使用起来更加简洁。

1.服务端

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include  <QtNetwork>
#if _MSC_VER >= 1600
#pragma execution_character_set("utf-8")
#endif

QString MainWindow::getLocalIP()
{
    //获取本机IPv4地址
    //! 本地主机名, QHostInfo 的静态函数 localHostName()可获取本机的主机名
    QString hostName = QHostInfo::localHostName();
    //! 返回指定的主机名的IP地址
    QHostInfo hostInfo = QHostInfo::fromName(hostName);
    QString localIP = "";
    //! 返回与 hostName()主机关联的IP地址列表
    QList<QHostAddress> addList = hostInfo.addresses();//

    for (int i = 0; i < addList.count(); i++)
    {
        QHostAddress aHost = addList.at(i);
        if (QAbstractSocket::IPv4Protocol == aHost.protocol())
        {
            //192.168.23.114
            localIP=aHost.toString();
            break;
        }
    }
    return localIP;
}

void MainWindow::closeEvent(QCloseEvent *event)
{//关闭窗口时停止监听
    if (tcpServer->isListening())
        tcpServer->close();;//停止网络监听
    event->accept();
}

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    LabListen=new QLabel("监听状态:");
    LabListen->setMinimumWidth(150);
    ui->statusBar->addWidget(LabListen);

    LabSocketState=new QLabel("Socket状态：");//
    LabSocketState->setMinimumWidth(200);
    ui->statusBar->addWidget(LabSocketState);
    //本机IP
    QString localIP = getLocalIP();
    this->setWindowTitle(this->windowTitle()+"----本机IP："+localIP);
    ui->comboIP->addItem(localIP);
    //! tcp服务端
    tcpServer = new QTcpServer(this);
    //! 如果有新的连接
    connect(tcpServer, SIGNAL(newConnection()), this, SLOT(onNewConnection()));
}

MainWindow::~MainWindow()
{
    delete ui;
}

//! 服务端有新的连接时
void MainWindow::onNewConnection()
{
//    ui->plainTextEdit->appendPlainText("有新连接");
    //! 创建socket,返回下一个等待接入的连接
    tcpSocket = tcpServer->nextPendingConnection();
    //! connectToHost()成功连接到服务器后发射此信号,连接成功后显示
    connect(tcpSocket, SIGNAL(connected()), this, SLOT(onClientConnected()));
    //! 客户端接入时
    onClientConnected();
    //! 当socket断开连接后发射此信号
    connect(tcpSocket, SIGNAL(disconnected()), this, SLOT(onClientDisconnected()));
    //! 当socket的状态变化时发射此信号,参数socketState表示了socket当前的状态
    connect(tcpSocket,SIGNAL(stateChanged(QAbstractSocket::SocketState)), this,
            SLOT(onSocketStateChange(QAbstractSocket::SocketState)));
    onSocketStateChange(tcpSocket->state());
    //! 当缓冲区有新数据需要读取时发射此信号，在此信号的槽函数里读取缓冲区的数据
    connect(tcpSocket, SIGNAL(readyRead()), this, SLOT(onSocketReadyRead()));
}

//socket状态变化时
void MainWindow::onSocketStateChange(QAbstractSocket::SocketState socketState)
{
    switch(socketState)
    {
    case QAbstractSocket::UnconnectedState:
        LabSocketState->setText("scoket状态：UnconnectedState");
        break;
    case QAbstractSocket::HostLookupState:
        LabSocketState->setText("scoket状态：HostLookupState");
        break;
    case QAbstractSocket::ConnectingState:
        LabSocketState->setText("scoket状态：ConnectingState");
        break;
    case QAbstractSocket::ConnectedState:
        LabSocketState->setText("scoket状态：ConnectedState");
        break;
    case QAbstractSocket::BoundState:
        LabSocketState->setText("scoket状态：BoundState");
        break;
    case QAbstractSocket::ClosingState:
        LabSocketState->setText("scoket状态：ClosingState");
        break;
    case QAbstractSocket::ListeningState:
        LabSocketState->setText("scoket状态：ListeningState");
    }
}

//客户端接入时
void MainWindow::onClientConnected()
{
    ui->plainTextEdit->appendPlainText("**client socket connected");
    ui->plainTextEdit->appendPlainText("**peer name:" + tcpSocket->peerName());
    //! 在已连接状态下，返回对方socket的地址
    ui->plainTextEdit->appendPlainText("**peer address:" + tcpSocket->peerAddress().toString());
    ui->plainTextEdit->appendPlainText("**peer port:" + QString::number(tcpSocket->peerPort()));
}

void MainWindow::onClientDisconnected()
{//客户端断开连接时
    ui->plainTextEdit->appendPlainText("**client socket disconnected");
    tcpSocket->deleteLater();
    //    deleteLater();//QObject::deleteLater();
}

void MainWindow::onSocketReadyRead()
{//读取缓冲区行文本
//    QStringList   lines;
    while(tcpSocket->canReadLine())
        ui->plainTextEdit->appendPlainText("[in] " + tcpSocket->readLine());
//        lines.append(clientConnection->readLine());
}

//开始监听
void MainWindow::on_actStart_triggered()
{
    //! IP地址
    QString IP = ui->comboIP->currentText();
    //! 端口
    quint16 port = ui->spinPort->value();
    QHostAddress addr(IP);
    tcpServer->listen(addr, port);//
//    tcpServer->listen(QHostAddress::LocalHost,port);// Equivalent to QHostAddress("127.0.0.1").
    ui->plainTextEdit->appendPlainText("**开始监听...");
    ui->plainTextEdit->appendPlainText("**服务器地址：" + tcpServer->serverAddress().toString());
    ui->plainTextEdit->appendPlainText("**服务器端口：" + QString::number(tcpServer->serverPort()));
    ui->actStart->setEnabled(false);
    ui->actStop->setEnabled(true);
    LabListen->setText("监听状态：正在监听");
}

void MainWindow::on_actStop_triggered()
{//停止监听
    if (tcpServer->isListening()) //tcpServer正在监听
    {
        tcpServer->close();//停止监听
        ui->actStart->setEnabled(true);
        ui->actStop->setEnabled(false);
        LabListen->setText("监听状态：已停止监听");
    }
}

void MainWindow::on_actClear_triggered()
{
    ui->plainTextEdit->clear();
}

void MainWindow::on_btnSend_clicked()
{//发送一行字符串，以换行符结束
    QString  msg=ui->editMsg->text();
    ui->plainTextEdit->appendPlainText("[out] "+msg);
    ui->editMsg->clear();
    ui->editMsg->setFocus();

    QByteArray  str=msg.toUtf8();
    str.append('\n');//添加一个换行符
    tcpSocket->write(str);
}

void MainWindow::on_actHostInfo_triggered()
{//获取本机地址
    QString hostName=QHostInfo::localHostName();//本地主机名
    ui->plainTextEdit->appendPlainText("本机主机名："+hostName+"\n");
    QHostInfo   hostInfo=QHostInfo::fromName(hostName);

    QList<QHostAddress> addList=hostInfo.addresses();//
    if (!addList.isEmpty())
    for (int i=0;i<addList.count();i++)
    {
        QHostAddress aHost=addList.at(i);
        if (QAbstractSocket::IPv4Protocol==aHost.protocol())
        {
            QString IP=aHost.toString();
            ui->plainTextEdit->appendPlainText("本机IP地址："+aHost.toString());
            if (ui->comboIP->findText(IP)<0)
                ui->comboIP->addItem(IP);
        }
    }

}

mainwindow.h

```cpp
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include    <QTcpServer>
#include    <QLabel>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
private:
    QLabel  *LabListen;//状态栏标签
    QLabel  *LabSocketState;//状态栏标签
    QTcpServer *tcpServer; //TCP服务器
    QTcpSocket *tcpSocket;//TCP通讯的Socket
    QString getLocalIP();//获取本机IP地址
protected:
    void   closeEvent(QCloseEvent *event);
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
private slots:
//自定义槽函数
    void    onNewConnection();//QTcpServer的newConnection()信号
    void    onSocketStateChange(QAbstractSocket::SocketState socketState);
    void    onClientConnected(); //Client Socket connected
    void    onClientDisconnected();//Client Socket disconnected
    void    onSocketReadyRead();//读取socket传入的数据
//UI生成的
    void on_actStart_triggered();
    void on_actStop_triggered();
    void on_actClear_triggered();
    void on_btnSend_clicked();
    void on_actHostInfo_triggered();
private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

1.客户端

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include  <QHostAddress>
#include  <QHostInfo>
#if _MSC_VER >= 1600
#pragma execution_character_set("utf-8")
#endif
QString MainWindow::getLocalIP()
{
    QString hostName = QHostInfo::localHostName();//本地主机名
    QHostInfo hostInfo = QHostInfo::fromName(hostName);
    QString localIP = "";
    QList<QHostAddress> addList = hostInfo.addresses();//
    for (int i = 0; i < addList.count(); i++)
    {
        QHostAddress aHost = addList.at(i);
        if (QAbstractSocket::IPv4Protocol == aHost.protocol())
        {
            localIP=aHost.toString();
            break;
        }
    }
    return localIP;
}
void MainWindow::closeEvent(QCloseEvent *event)
{
    if (tcpClient->state()==QAbstractSocket::ConnectedState)
        tcpClient->disconnectFromHost();
    event->accept();
}

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    tcpClient = new QTcpSocket(this); //创建socket变量
    LabSocketState=new QLabel("Socket状态：");//状态栏标签
    LabSocketState->setMinimumWidth(250);
    ui->statusBar->addWidget(LabSocketState);
    //本机IP
    QString localIP = getLocalIP();
    this->setWindowTitle(this->windowTitle() + "----本机IP：" + localIP);
    ui->comboServer->addItem(localIP);

    connect(tcpClient,SIGNAL(connected()),this,SLOT(onConnected()));
    connect(tcpClient,SIGNAL(disconnected()),this,SLOT(onDisconnected()));
    connect(tcpClient,SIGNAL(stateChanged(QAbstractSocket::SocketState)),this,
            SLOT(onSocketStateChange(QAbstractSocket::SocketState)));
    connect(tcpClient,SIGNAL(readyRead()),this,SLOT(onSocketReadyRead()));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::onConnected()
{ //connected()信号槽函数
    ui->plainTextEdit->appendPlainText("**已连接到服务器");
    ui->plainTextEdit->appendPlainText("**peer address:" + tcpClient->peerAddress().toString());
    ui->plainTextEdit->appendPlainText("**peer port:" + QString::number(tcpClient->peerPort()));
    ui->actConnect->setEnabled(false);
    ui->actDisconnect->setEnabled(true);
}

void MainWindow::onDisconnected()
{//disConnected()信号槽函数
    ui->plainTextEdit->appendPlainText("**已断开与服务器的连接");
    ui->actConnect->setEnabled(true);
    ui->actDisconnect->setEnabled(false);
}

void MainWindow::onSocketReadyRead()
{//readyRead()信号槽函数
    while(tcpClient->canReadLine())
        ui->plainTextEdit->appendPlainText("[in] "+tcpClient->readLine());
}

void MainWindow::onSocketStateChange(QAbstractSocket::SocketState socketState)
{//stateChange()信号槽函数
    switch(socketState)
    {
    case QAbstractSocket::UnconnectedState:
        LabSocketState->setText("scoket状态：UnconnectedState");
        break;
    case QAbstractSocket::HostLookupState:
        LabSocketState->setText("scoket状态：HostLookupState");
        break;
    case QAbstractSocket::ConnectingState:
        LabSocketState->setText("scoket状态：ConnectingState");
        break;
    case QAbstractSocket::ConnectedState:
        LabSocketState->setText("scoket状态：ConnectedState");
        break;
    case QAbstractSocket::BoundState:
        LabSocketState->setText("scoket状态：BoundState");
        break;
    case QAbstractSocket::ClosingState:
        LabSocketState->setText("scoket状态：ClosingState");
        break;
    case QAbstractSocket::ListeningState:
        LabSocketState->setText("scoket状态：ListeningState");
    }
}

void MainWindow::on_actConnect_triggered()
{//连接到服务器
    QString     addr=ui->comboServer->currentText();
    quint16     port=ui->spinPort->value();
    tcpClient->connectToHost(addr,port);
//    tcpClient->connectToHost(QHostAddress::LocalHost,port);
}

void MainWindow::on_actDisconnect_triggered()
{//断开与服务器的连接
    if (tcpClient->state()==QAbstractSocket::ConnectedState)
        tcpClient->disconnectFromHost();
}

void MainWindow::on_actClear_triggered()
{
    ui->plainTextEdit->clear();
}

void MainWindow::on_btnSend_clicked()
{//发送数据
    QString  msg=ui->editMsg->text();
    ui->plainTextEdit->appendPlainText("[out] "+msg);
    ui->editMsg->clear();
    ui->editMsg->setFocus();
    QByteArray str = msg.toUtf8();
    str.append('\n');
    tcpClient->write(str);
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include    <QTcpSocket>
#include    <QLabel>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
private:
    QTcpSocket  *tcpClient;  //socket
    QLabel  *LabSocketState;  //状态栏显示标签

    QString getLocalIP();//获取本机IP地址
protected:
    void    closeEvent(QCloseEvent *event);
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
//自定义槽函数
    void    onConnected();
    void    onDisconnected();
    void    onSocketStateChange(QAbstractSocket::SocketState socketState);
    void    onSocketReadyRead();//读取socket传入的数据
//
    void on_actConnect_triggered();

    void on_actDisconnect_triggered();

    void on_actClear_triggered();

    void on_btnSend_clicked();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

总结

以上就是今天要讲的内容，本文整理了三种实现TCP通信的方法，从上层到偏底层，对于新手理解通信原理有极大帮助。