原标题：在C++ Builder中用socket api来写网络通讯程序（同时支持TCP和UDP协议）
原文:  http://www.csdn.net/develop/read_article.asp?id=19883

在7月4日看完sockcomp.pas后，我决定用socket api来写一个客户端和服务器并且同时支持TCP,UDP协议，于是我就去做，现将代码贴出来（已调试通过）
Socket api Client:

#ifndef UDPClientH
#define UDPClientH
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <stdio.h>
#include "CCEdit.h"
#define WM_SOCK WM_USER+100
class TLANForm : public TForm
{
__published: // IDE-managed Components
   TEdit *Port;
   TLabel *Label1;
   TLabel *Label2;
   TComboBox *Prot;
   TButton *Button1;
   TLabel *Label3;
   TEdit *Addr;
   TCCEdit *TxtEdit;
   void __fastcall FormCreate(TObject *Sender);
   void __fastcall Button1Click(TObject *Sender);
   void __fastcall FormDestroy(TObject *Sender);
private: // User declarations
   void __fastcall OnRecv(TMessage &Message);
public:  // User declarations
   __fastcall TLANForm(TComponent* Owner);
   BEGIN_MESSAGE_MAP //建立消息映射表
      VCL_MESSAGE_HANDLER(WM_SOCK,TMessage,OnRecv);//指定消息处理函数
   END_MESSAGE_MAP(TForm);//映射表结束
};
extern PACKAGE TLANForm *LANForm;
#endif

.cpp File

#include <vcl.h>
#pragma hdrstop
#include "UDPClient.h"
#include "WinSock.h"
#pragma package(smart_init)
#pragma link "CCEdit"
#pragma resource "*.dfm"
TLANForm *LANForm;
enum PROTO {TCP=0,UDP=1};//枚举,socket协议类型
SOCKET m_Socket=INVALID_SOCKET; //定义一个socket对象
PROTO m_Protocol=TCP; //socket类型变量
__fastcall TLANForm::TLANForm(TComponent* Owner)
   : TForm(Owner)
{

}
void __fastcall TLANForm::FormCreate(TObject *Sender)
{
   ::SendMessage(Prot->Handle,CB_SETCURSEL,0,0);
}
void __fastcall TLANForm::OnRecv(TMessage &Message)
{
   char buf[4096];
   int nLen;
   struct sockaddr_in from;
   int nLength=sizeof(struct sockaddr_in);//结构长度
   switch(WSAGETSELECTEVENT(Message.LParam))
   {
      case FD_READ://收到消息
         switch(m_Protocol)
         {
            case TCP:
               nLen=recv(m_Socket,buf,4096,0);//接收
               if(nLen>0){
                  buf[nLen]='\0';
                  TxtEdit->Text="Received Length:"+String(nLen)+"\r\n"+StrPas(buf);
               }
               break;
            case UDP:
               nLen=recvfrom(m_Socket,buf,4096,0,(struct sockaddr*)&from,&nLength);
               if(nLen>0){
                  buf[nLen]='\0';
                  TxtEdit->Text="Received Length:"+String(nLen)+"\r\n"+StrPas(buf);
               }
               break;
         }
         break;
      case FD_CLOSE://关闭连接消息
         closesocket(m_Socket);
         break;
   }
}

void __fastcall TLANForm::Button1Click(TObject *Sender)
{
   char szTmp[256],buf[4096];
   int nSize=0;
   UINT m_Port;
   AnsiString addr;
   addr=Addr->Text.Trim();
   if(addr.IsEmpty()){//IP为空结束
      ::MessageBox(0,"Please enter the server IP!","Error",MB_OK+MB_ICONERROR);
      return;
   }
   unsigned long nAddr=inet_addr(addr.c_str());
   if(nAddr==INADDR_NONE){//IP地址无效
      ::MessageBox(0,"Bad Internet IP!","Error",MB_OK+MB_ICONERROR);
      return;}

try
   {
      m_Port=Port->Text.ToInt();//得到端口
   }
   catch(Exception &e)
   {
      ::MessageBox(0,e.Message.c_str(),"Error",MB_OK+MB_ICONERROR);
      return;
   }
   switch(Prot->ItemIndex)//得到协议类型
   {
      case 0:
         m_Protocol=TCP;
         break;
      case 1:
         m_Protocol=UDP;
         break;
   }
   if(TxtEdit->Text.IsEmpty()){//发送内容
      ::MessageBox(0,"Please enter the text you want to send!","Error",MB_OK+MB_ICONERROR);
      return;}

//1.初始化Winsock
   WSAData wsaData;
   ::ZeroMemory(&wsaData,sizeof(WSAData)); //0填充
   WORD version=MAKEWORD(2,0);
   if(::WSAStartup(version,&wsaData)){ //初始化
      sprintf(szTmp,"Failed to initial winsock enviroment!,error no:%d",::WSAGetLastError());
      return;}

//Obtain the active connection
   char ComputerName[255];
   gethostname(ComputerName,255);
   struct hostent* he=gethostbyname(ComputerName);
   if(!he){
      sprintf(szTmp,"Failed to get information to host!","Error",MB_OK+MB_ICONERROR);
      ::WSACleanup();
      return;
   }
   //2.建立新socket
   m_Socket=INVALID_SOCKET;
   switch(m_Protocol)
   {
      case TCP:
         m_Socket=socket(AF_INET,SOCK_STREAM,0);
         break;
      case UDP:
         m_Socket=socket(AF_INET,SOCK_DGRAM,0);
         break;
   }
   if(m_Socket==INVALID_SOCKET){//建立socket失败
      sprintf(szTmp,"Failed to create a new socket!,error no:%d",::WSAGetLastError());
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      ::WSACleanup();
      return;
   }
   //3.绑定SOCKET
   struct sockaddr_in client;
   unsigned long nClient;
   memcpy(&nClient,he->h_addr_list[0],sizeof(int));
   if(nClient==INADDR_NONE){
      sprintf(szTmp,"Failed to obtain the local machine's IP!","Error",MB_OK+MB_ICONERROR);
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      closesocket(m_Socket);
      ::WSACleanup();
      return;
   }
   client.sin_family=AF_INET;
   client.sin_port=0;
   client.sin_addr.S_un.S_addr=(int)nClient;
   if(bind(m_Socket,(struct sockaddr*)&client,sizeof(struct sockaddr))){
      sprintf(szTmp,"Failed to bind socket!","Error",MB_OK+MB_ICONERROR);
      closesocket(m_Socket);
      ::WSACleanup();
      return;}
 
   struct sockaddr_in To;
   To.sin_family=AF_INET;
   To.sin_port=htons(m_Port);
   To.sin_addr.S_un.S_addr=(int)nAddr;
   fd_set FDSET;
   FD_ZERO(&FDSET);
   FD_SET(m_Socket,&FDSET);

//4.连接远程主机
   if(m_Protocol==TCP){
      if(connect(m_Socket,(struct sockaddr*)&To,sizeof(struct sockaddr))){
         sprintf(szTmp,"Failed to connect the object!,error no:%d",::WSAGetLastError());
         ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
         closesocket(m_Socket);
         ::WSACleanup();
         return;
      }
      int nError=select(1,0,&FDSET,0,0);
      if(nError<=0){
      sprintf(szTmp,"Failed to select socket!,error no:%d",::WSAGetLastError());
      closesocket(m_Socket);
      ::WSACleanup();
      return;}
   }
   //5.发送数据
   int nLen=TxtEdit->Text.Length();
   if(nLen>4096){
      sprintf(szTmp,"The buffer is too size to send,it shoud not be more than 4096 bytes!");
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      closesocket(m_Socket);
      ::WSACleanup();
      return;
   }
   strncpy(buf,TxtEdit->Text.c_str(),nLen);
   switch(m_Protocol)
   {
      case TCP:
         nSize=send(m_Socket,buf,nLen,0);
         //ShowMessage(nSize);
         break;
      case UDP:
         nSize=sendto(m_Socket,buf,nLen,0,(struct sockaddr*)&To,sizeof(struct sockaddr));
         //ShowMessage(nSize);
         break;

}
   if(::WSAAsyncSelect(m_Socket,Handle,WM_SOCK,FD_READ|FD_CLOSE)){
      sprintf(szTmp,"Failed to register socket event!,error no:%d",::WSAGetLastError());
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      closesocket(m_Socket);
      ::WSACleanup();
      return;}
}

void __fastcall TLANForm::FormDestroy(TObject *Sender)//断开连接
{
   closesocket(m_Socket);
   ::WSACleanup();
}

Socket api Server:
.h File
#ifndef UDPServerH
#define UDPServerH
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <stdio.h>
#include "WinSock.h"
/*#define WM_SOCKET WM_USER+1000
#define INITSOCKETSUCCESS 0
#define INITSOCKETFAILURE 1
#define CREATELISTENSOCKETSUCCESS 2
#define CREATELISTENSOCKETFAILURE 3
#define SETLISTENSOCKETSUCCESS 4
#define SETLISTENSOCKETFAILURE 5
#define BINDLISTENSOCKETSUCCESS 6
#define BINDLISTENSOCKETFAILURE 7
#define LISTENSOCKETSUCCESS 8
#define LISTENSOCKETFAILURE 9
#define ACCEPTSOCKETSUCCESS 10
#define ACCEPTSOCKETFAILURE 11
*/
class TPSTNForm : public TForm
{
__published: // IDE-managed Components
   TEdit *Port;
   TLabel *Label1;
   TMemo *Memo1;
   TButton *Button1;
   TButton *Button2;
   TLabel *Label2;
   TComboBox *Prot;
   void __fastcall Button1Click(TObject *Sender);
   void __fastcall Button2Click(TObject *Sender);
   void __fastcall FormCreate(TObject *Sender);
   void __fastcall FormDestroy(TObject *Sender);
private: // User declarations
public:  // User declarations
   __fastcall TPSTNForm(TComponent* Owner);
};
enum PROTO {TCP,UDP};
class TCommunication:public TThread    //Communication Thread
{
private:
   SOCKET m_AcceptSocket;
   char szTmp[256];//ERROR MESSAGE
public:
   __fastcall TCommunication(SOCKET m_Socket,bool CreateSuspended);
   __fastcall ~TCommunication();
protected:
   virtual void __fastcall Execute();
};
class TListenThread:public TThread //Listen Thread
{
private:
   WSAData wsaData;
   struct sockaddr_in server;
   fd_set FDS;
   UINT m_Port;
   PROTO m_Protocol;
   char szTmp[256];//Error Message
public:
   SOCKET m_Socket;
   void __fastcall DoError();
   void __fastcall InitSocket();
   void __fastcall CreateListenSocket();
   void __fastcall SetListenSocket();
   void __fastcall BindListenSocket();
   void __fastcall ListenSocket();

public:
   __fastcall TListenThread(PROTO m_ProtocolA,UINT m_PortA,bool CreateSuspended);
   virtual __fastcall ~TListenThread();
protected:
   virtual void __fastcall Execute();
};
extern PACKAGE TPSTNForm *PSTNForm;
#endif
.cpp File
#include <vcl.h>
#pragma hdrstop
#include "UDPServer.h"
#pragma package(smart_init)
#pragma resource "*.dfm"
TPSTNForm *PSTNForm;
TListenThread *pThread=0;
//******************************CLASS TCommunication For TCP****************************************************
__fastcall TCommunication::TCommunication(SOCKET m_Socket,bool CreateSuspended):TThread(FALSE)
{
   m_AcceptSocket=m_Socket;
   szTmp[0]='\0';
   FreeOnTerminate=true;
}
__fastcall TCommunication::~TCommunication()
{
  // closesocket(m_AcceptSocket);
}
void __fastcall TCommunication::Execute()
{
   char buf[4096];
   int nSize=0;
   nSize=recv(m_AcceptSocket,(char FAR*)buf,4096,0);
   if(nSize>0)
   {
      buf[nSize]='\0';
      //Display
      PSTNForm->Memo1->Lines->Add("Received Length:"+String(nSize));
      PSTNForm->Memo1->Lines->Add("Received:"+StrPas(buf));
      //Deliver
      ::Sleep(100);
      send(m_AcceptSocket,buf,nSize,0);
   }

}
//******************************CLASS TListenThread*****************************************************
__fastcall TListenThread::TListenThread(PROTO m_ProtocolA,UINT m_PortA,bool CreateSuspended):TThread(FALSE)
{
   m_Socket=INVALID_SOCKET;
   m_Port=m_PortA;
   m_Protocol=m_ProtocolA;
   szTmp[0]='\0';
   ::ZeroMemory(&wsaData,sizeof(WSAData));
   ::ZeroMemory(&server,sizeof(struct sockaddr_in));
   FreeOnTerminate=TRUE;//Automatically delete while terminating.
}
__fastcall TListenThread::~TListenThread()
{
   closesocket(m_Socket);
   ::WSACleanup();
   m_Socket=INVALID_SOCKET;
   m_Port=0;
   m_Protocol=TCP;
   szTmp[0]='\0';
   ::ZeroMemory(&wsaData,sizeof(WSAData));
   ::ZeroMemory(&server,sizeof(struct sockaddr_in));
}
void __fastcall TListenThread::DoError()
{
   if(m_Socket!=INVALID_SOCKET) closesocket(m_Socket);
   WSACleanup();
   return;
}
void __fastcall TListenThread::InitSocket()
{
   WORD version=MAKEWORD(2,0);
   if(::WSAStartup(version,&wsaData)){
      sprintf(szTmp,"Failed to intiailize socket,error no:%d",::WSAGetLastError());
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      DoError();
      return;
   }
}
void __fastcall TListenThread::CreateListenSocket()
{
   switch(m_Protocol)
   {
      case UDP:
         m_Socket=socket(AF_INET,SOCK_DGRAM,0);
         break;
      case TCP:
         m_Socket=socket(AF_INET,SOCK_STREAM,0);
         break;
      default:
         sprintf(szTmp,"Error protocol!");
         ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
         DoError();
         break;
   }
   if(m_Socket==INVALID_SOCKET){
      sprintf(szTmp,"Failed to create socket!");
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      DoError();
      return;
   }
}
void __fastcall TListenThread::SetListenSocket()
{
   server.sin_family=AF_INET;
   server.sin_port=htons(m_Port);
   server.sin_addr.S_un.S_addr=INADDR_ANY;
   int NewOpenType=SO_SYNCHRONOUS_NONALERT;
   if(setsockopt(INVALID_SOCKET,SOL_SOCKET,SO_OPENTYPE,(char*)&NewOpenType,4)){
      sprintf(szTmp,"Set socket option error,error no:%d",::WSAGetLastError());
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      DoError();
      return;
   }
}
void __fastcall TListenThread::BindListenSocket()
{
    if(bind(m_Socket,(sockaddr*)&server,sizeof(struct sockaddr_in))){
      sprintf(szTmp,"Failed to bind socket,error no:%d",::WSAGetLastError());
      ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
      DoError();
      return;
   }

}
void __fastcall TListenThread::ListenSocket()
{
  if(listen(m_Socket,SOMAXCONN)){
     sprintf(szTmp,"listen error,error no:%d",::WSAGetLastError());
     ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
     DoError();
     return;
  }
  //Determine whether there is any connection
  FD_ZERO(&FDS);
  FD_SET(m_Socket,&FDS);
}
void __fastcall TListenThread::Execute()
{
   char buf[4096];
   struct sockaddr_in from; //for UDP
   int nLen=sizeof(from),nSize=0;  //for UDP
   InitSocket();
   CreateListenSocket();
   SetListenSocket();
   BindListenSocket();
   if(m_Protocol==UDP){
      while(!Terminated){
         int nSize=recvfrom(m_Socket,buf,4096,0,(struct sockaddr*)&from,&nLen);
         if(nSize>0){
            buf[nSize]='\0';
            PSTNForm->Memo1->Lines->Add("Received Length:"+String(nSize));
            PSTNForm->Memo1->Lines->Add("Received:"+StrPas(buf));
            ::Sleep(100);
            sendto(m_Socket,buf,nSize,0,(struct sockaddr*)&from,sizeof(struct sockaddr_in));
         }
         else return;

}
   }
   ListenSocket();
   struct sockaddr_in client;
   int nLength=sizeof(struct sockaddr_in);
   while(!Terminated){
      int nError=select(1,&FDS,0,0,0);
      if(nError<=0) Terminate();
      SOCKET m_AcceptSocket=accept(m_Socket,(struct sockaddr*)&client,&nLength);
      if(m_AcceptSocket==INVALID_SOCKET){
         sprintf(szTmp,"Failed to execute accept,error no:%d",::WSAGetLastError());
         ::MessageBox(0,szTmp,"Error",MB_OK+MB_ICONERROR);
         DoError();
         Terminate();
         return;
      }
      TCommunication *pCThread=new TCommunication(m_AcceptSocket,FALSE);
      pCThread->Terminate();
      pCThread->WaitFor();
   }
}
//************************PSTNForm*********************************************//
__fastcall TPSTNForm::TPSTNForm(TComponent* Owner)
   : TForm(Owner)
{
}
void __fastcall TPSTNForm::Button1Click(TObject *Sender)
{
   Close();
}
void __fastcall TPSTNForm::Button2Click(TObject *Sender)
{
   if(pThread){
      pThread->Suspend();
      pThread->Terminate();
      delete pThread;
      pThread=0;
   }
   UINT m_Port;
   try
   {
      m_Port=Port->Text.ToInt();
   }
   catch(Exception &e)
   {
      ::MessageBox(0,e.Message.c_str(),"Error",MB_OK+MB_ICONERROR);
      return;
   }
   PROTO m_Protocol;
   switch(Prot->ItemIndex)
   {
      case 0:
         m_Protocol=TCP;
         break;
      case 1:
         m_Protocol=UDP;
         break;
      default:
         break;
   }
   pThread=new TListenThread(m_Protocol,m_Port,FALSE);
   //pThread->Terminate();
}
void __fastcall TPSTNForm::FormCreate(TObject *Sender)
{
   ::SendMessage(Prot->Handle,CB_SETCURSEL,0,1);
}

void __fastcall TPSTNForm::FormDestroy(TObject *Sender)
{
   if(pThread){
      pThread->Suspend();
      pThread->Terminate();}
}