我在使用服务器-客户端 FTP 模拟程序时遇到了一些问题。该程序不断给我“未定义的引用”错误。我在 Windows 上使用 C::B 10.05，并尝试包括 winsock.h、winsock2.h 以及我在互联网上找到的更多解决方案，但没有奏效。这是源代码。
非常感谢任何帮助。
谢谢。
//Router Head file
#include <winsock.h>
#include <fstream>
#include <iostream>
#include <time.h>
#include <winsock2.h>
#include <list>
#include <stdio.h>
#define MAXBUFSIZE 2048 //maximum packet size
#define MAXHOSTNAMELEN 256 //maximum length of host name
#define ROUTER_PORT1 7000 //router port number 1
#define ROUTER_PORT2 7001 //router port number 2
#define PEER_PORT1 5000 //port number of peer host 1
#define PEER_PORT2 5001 //port number of peer host 2
#define TIMEOUT_USEC 300000 //time-out value
#define TRACE 1
using namespace std ;
struct EVENT_LIST
{
bool empty;
DWORD count; //count is the packet number
short destination; //destination of this packet
int len; //length of this packet
char Buffer[MAXBUFSIZE]; //buffer for packet
};
class Router
{
public:
char localhost[MAXHOSTNAMELEN]; //local host name
Router(char *fn="log.txt");
~Router();
void Run();
private:
ofstream fout;
float damage_rate, delay_rate; //damage rate: dropped and delayed
SOCKET Sock1, Sock2; //sockets used for communcation with peer host 1 and 2
EVENT_LIST FileBuf; //buffer for delayed packets
protected:
SOCKADDR_IN sa_in_peer1; // address structure for peer host 1 address
SOCKADDR_IN sa_in_peer2; // address structure for peer host 2 address
bool IsDamage() const;
bool IsDelayed() const;
void SendProc();
};
//Router.cpp
//////////////////////////////////////////////////////////
//
// Router Constructor
// arguements:
// fn: A string of log file name
//
//////////////////////////////////////////////////////////
Router::Router(char *fn) //Constructor
{
WSADATA wsadata;
HOSTENT* hp;
char peer_name1[MAXHOSTNAMELEN], peer_name2[MAXHOSTNAMELEN];
SOCKADDR_IN sa_in;
FileBuf.empty=true;
try
{
if (WSAStartup(0x0202,&wsadata)!=0)
throw "Error in starting WSAStartup()\n";
}
//Display any needed error response.
catch (char *str) { cerr<<str<<":"<<dec<<WSAGetLastError()<<endl; return;}
//Get Host name
gethostname(localhost,MAXHOSTNAMELEN);
cout<<"Router starting on host:"<<localhost<<endl<<flush;
//Open the log file
fout.open(fn);
try
{
//Create the Udp Sock1
if((Sock1 = socket(AF_INET,SOCK_DGRAM,0))==INVALID_SOCKET)
throw "Create UDP Socket1 failed\n";
//Fill-in UDP Port and Address info.
sa_in.sin_family = AF_INET;
sa_in.sin_port = htons(ROUTER_PORT1);
sa_in.sin_addr.s_addr = htonl(INADDR_ANY);
//Bind the UDP port1
if (bind(Sock1,(LPSOCKADDR)&sa_in,sizeof(sa_in)) == SOCKET_ERROR)
throw "can't bind the socket1";
//Create the Udp Sock2
if((Sock2 = socket(AF_INET,SOCK_DGRAM,0))==INVALID_SOCKET)
throw "Create UDP Socket2 failed\n";
//Fill-in UDP Port and Address info.
sa_in.sin_family = AF_INET;
sa_in.sin_port = htons(ROUTER_PORT2);
sa_in.sin_addr.s_addr = htonl(INADDR_ANY);
//Bind the UDP port2
if (bind(Sock2,(LPSOCKADDR)&sa_in,sizeof(sa_in)) == SOCKET_ERROR)
throw "can't bind the socket2";
cout<<"\nPlease enter the first peer host name:"<<flush; //enter the dropping rate.
cin>>peer_name1;
cout<<"\nPlease enter the second peer host name:"<<flush; //enter the dropping rate.
cin>>peer_name2;
cout<<"\nPlease enter the drop rate:"<<flush; //enter the dropping rate.
cin>>damage_rate;
cout<<"\nPlease enter the delay rate:"<<flush; //enter the dropping rate.
cin>>delay_rate;
//creat peer host1
if((hp=gethostbyname(peer_name1)) == NULL)
throw "get server name failed\n";
memset(&sa_in_peer1,0,sizeof(sa_in_peer1));
memcpy(&sa_in_peer1.sin_addr,hp->h_addr,hp->h_length);
sa_in_peer1.sin_family = hp->h_addrtype;
sa_in_peer1.sin_port = htons(PEER_PORT1);
//creat peer host2
if((hp=gethostbyname(peer_name2)) == NULL)
throw "get client name failed\n";
memset(&sa_in_peer2,0,sizeof(sa_in_peer2));
memcpy(&sa_in_peer2.sin_addr,hp->h_addr,hp->h_length);
sa_in_peer2.sin_family = hp->h_addrtype;
sa_in_peer2.sin_port = htons(PEER_PORT2);
if (TRACE)
{
fout<<"Peer host 1: "<<peer_name1<<endl;
fout<<"Peer host 2: "<<peer_name2<<endl;
fout<<"Damage Rate: "<<damage_rate<<endl;
}
}
catch (char *str) {cerr<<str<<":"<<dec<<WSAGetLastError()<<endl; exit(1);}
srand( (unsigned)time( NULL ) );
};
//////////////////////////////////////////////////////////
//
// Router::IsDamage
// The function that generates random damages according to damage rate.
//
//////////////////////////////////////////////////////////
bool Router::IsDamage() const
{
return ( (((float)rand())/RAND_MAX) < ((float)damage_rate/100));
}
//////////////////////////////////////////////////////////
//
// Router::IsDelayed
// The function that generates random delayed according to delay rate.
//
//////////////////////////////////////////////////////////
bool Router::IsDelayed() const
{
return ( (((float)rand())/RAND_MAX) < ((float)delay_rate/100));
};
//////////////////////////////////////////////////////////
//
// Router::Run
// The function receives packets from peer hosts and forwards to destinations.
// It also drops packets and stores delayed packets for future sending.
// It calls SendProc to send delayed packets.
//
//////////////////////////////////////////////////////////
void Router::Run()
{
fd_set readfds;
struct timeval *tp=new timeval;
SOCKADDR from;
int RetVal, fromlen, recvlen, wait_count;
EVENT_LIST temp;
DWORD CurrentTime, count1, count2;
count1=0;
count2=0;
wait_count=0;
tp->tv_sec=0;
tp->tv_usec=TIMEOUT_USEC;
while (1)
{
try
{
FD_ZERO(&readfds);
FD_SET(Sock1,&readfds);
FD_SET(Sock2,&readfds);
fromlen=sizeof(from);
if((RetVal=select(1,&readfds,NULL,NULL,tp))==SOCKET_ERROR) //check for incoming packets.
throw "Timer error!";
else if(RetVal>0) //There are incoming packets.
{
if(!FileBuf.empty) wait_count++;
if(FD_ISSET(Sock1, &readfds)) //incoming packet from peer host 1
{
if((recvlen=recvfrom(Sock1, temp.Buffer, sizeof(temp.Buffer), 0, &from, &fromlen))==SOCKET_ERROR)
throw " Get buffer error!";
if (TRACE)
{
fout<<"Router: Receive packet "<<count1<<" from peer host 1"<<endl;
cout<<"Router: Receive packet "<<count1<<" from peer host 1"<<endl;
}
temp.count=count1;
count1++;
temp.destination=2;
}
else if(FD_ISSET(Sock2, &readfds)) //incoming packet from peer host 2
{
if((recvlen=recvfrom(Sock2, temp.Buffer, sizeof(temp.Buffer), 0, &from, &fromlen))==SOCKET_ERROR)
throw " Get buffer error!";
if (TRACE)
{
fout<<"Router: Receive packet "<<count2<<" from peer host 2"<<endl;
cout<<"Router: Receive packet "<<count2<<" from peer host 2"<<endl;
}
temp.count=count2;
count2++;
temp.destination=1;
}
else continue;
temp.len=recvlen;
CurrentTime=GetTickCount();
if(FileBuf.empty&&IsDelayed()) //if the packet is delayed.
{
FileBuf=temp;
FileBuf.empty=false;
if (TRACE)
{
fout<<"Router: Packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1)<<" has been delayed!"<<endl;
cout<<"Router: Packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1)<<" has been delayed!"<<endl;
}
}
else if(IsDamage()) //if the packet is dropped: dropping packet by no forwarding the packet.
{
if (TRACE)
{
fout<<"Router: Packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1)<<" has been dropped by router!"<<endl;
cout<<"Router: Packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1)<<" has been dropped by router!"<<endl;
}
}
else //otherwise, packet is forwarded to destination
{
if(temp.destination==1) //forward packets received from 2 to 1.
{
if(sendto(Sock1, temp.Buffer, temp.len,0,(SOCKADDR*)&sa_in_peer1,sizeof(sa_in_peer1))==SOCKET_ERROR)
throw "Send packet error!";
if (TRACE)
{
fout<<"Router: Send packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1) <<" to host "<<temp.destination<<endl;
cout<<"Router: Send packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1) <<" to host "<<temp.destination<<endl;
}
if(!FileBuf.empty&&FileBuf.destination==1)
{
wait_count=0;
SendProc();
}
}
else
{ //forward packets received from 1 to 2.
if(sendto(Sock2, temp.Buffer, temp.len,0,(SOCKADDR*)&sa_in_peer2,sizeof(sa_in_peer2))==SOCKET_ERROR)
throw "Send packet error1";
if (TRACE)
{
fout<<"Router: Send packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1) <<" to host "<<temp.destination<<endl;
cout<<"Router: Send packet "<<temp.count<<" received from peer host "<<(temp.destination==1?2:1) <<" to host "<<temp.destination<<endl;
}
if(!FileBuf.empty&&FileBuf.destination==2)
{
wait_count=0;
SendProc();
}
}
}
}
else //If there is no incoming packet and there is a delayed packets storing in buffer for 3 cycle times (about 0.9 second), call SendProc to send delayed packet.
{
if(!FileBuf.empty)
{
wait_count++;
if(wait_count>=3)
{
SendProc();
wait_count=0;
}
}
}
} //end of try
catch(char *str) {cerr<<str<<":"<<dec<<WSAGetLastError()<<endl;}
}//end of while
};
//////////////////////////////////////////////////////////
//
// Router::SendProc
// Send delayed packets to the destinations.
//
//////////////////////////////////////////////////////////
void Router::SendProc()
{
try
{
if(FileBuf.destination==1)
{
if(sendto(Sock1, FileBuf.Buffer, FileBuf.len,0,(SOCKADDR*)&sa_in_peer1,sizeof(sa_in_peer1))==SOCKET_ERROR)
throw "Send packet error!";
}
else
{
if(sendto(Sock2, FileBuf.Buffer, FileBuf.len,0,(SOCKADDR*)&sa_in_peer2,sizeof(sa_in_peer2))==SOCKET_ERROR)
throw "Send packet error!";
}
if (TRACE)
{
fout<<"Router: Send delayed packet "<<FileBuf.count<<" received from peer host "<<(FileBuf.destination==1?2:1)<<" to host "<<FileBuf.destination<<endl;
cout<<"Router: Send delayed packet "<<FileBuf.count<<" received from peer host "<<(FileBuf.destination==1?2:1)<<" to host "<<FileBuf.destination<<endl;
}
}
catch(char *str){cerr<<str<<":"<<dec<<WSAGetLastError()<<endl;}
FileBuf.empty=true;
};
//////////////////////////////////////////////////////////
//
// Router Destructor
// arguements:
// fn: A string of log file name
//
//////////////////////////////////////////////////////////
Router :: ~Router()
{
closesocket(Sock1);
closesocket(Sock2);
/* When done, uninstall winsock.dll (WSACleanup()) and exit */
WSACleanup();
//close log file
fout.close();
};
//////////////////////////////////////////////////////////
//
// Main function
//
//////////////////////////////////////////////////////////
int main()
{
Router router;
router.Run();
return 0;
}
最佳答案
“ undefined reference ”错误是链接器错误。链接器错误无法通过包含其他头文件来解决。从概念上讲，头文件包含函数的声明(函数的名称、参数的类型、返回值的类型)。您包含头文件，以便您可以引用程序中头文件中声明的函数。在链接期间，这些引用被解析为指向包含这些函数的实际实现的库。
当您收到“ undefined reference ”错误时，这意味着链接器无法在链接器被告知链接的任何库中找到您在代码中引用的函数的实现。为了解决这个问题，你必须找到实现缺失函数的库，并告诉编译器链接到这个库。
当我编译你的程序时，我得到以下错误:
error LNK2019: unresolved external symbol "___WSAFDIsSet@8" referenced in function ""public: void __thiscall Router::Run(void)" (?Run@Router@@QAEXXZ)".
error LNK2019: unresolved external symbol "__imp__bind@12" referenced in function "__catch$??0Router@@QAE@PBD@Z$0".
error LNK2019: unresolved external symbol "__imp__closesocket@4" referenced in function ""public: __thiscall Router::~Router(void)" (??1Router@@QAE@XZ)".
error LNK2019: unresolved external symbol "__imp__htonl@4" referenced in function "__catch$??0Router@@QAE@PBD@Z$0".
error LNK2019: unresolved external symbol "__imp__htons@4" referenced in function "__catch$??0Router@@QAE@PBD@Z$0".
error LNK2019: unresolved external symbol "__imp__recvfrom@24" referenced in function ""public: void __thiscall Router::Run(void)" (?Run@Router@@QAEXXZ)".
error LNK2019: unresolved external symbol "__imp__select@20" referenced in function ""public: void __thiscall Router::Run(void)" (?Run@Router@@QAEXXZ)".
error LNK2019: unresolved external symbol "__imp__sendto@24" referenced in function ""public: void __thiscall Router::Run(void)" (?Run@Router@@QAEXXZ)".
error LNK2019: unresolved external symbol "__imp__socket@12" referenced in function "__catch$??0Router@@QAE@PBD@Z$0".
error LNK2019: unresolved external symbol "__imp__gethostbyname@4" referenced in function "__catch$??0Router@@QAE@PBD@Z$0".
error LNK2019: unresolved external symbol "__imp__gethostname@8" referenced in function "__catch$??0Router@@QAE@PBD@Z$0".
error LNK2019: unresolved external symbol "__imp__WSAStartup@8" referenced in function ""public: __thiscall Router::Router(char const *)" (??0Router@@QAE@PBD@Z)".
error LNK2019: unresolved external symbol "__imp__WSACleanup@0" referenced in function ""public: __thiscall Router::~Router(void)" (??1Router@@QAE@XZ)".
error LNK2019: unresolved external symbol "__imp__WSAGetLastError@0" referenced in function "__catch$??0Router@@QAE@PBD@Z$0".
Ws2_32.lib .我们现在必须告诉编译器链接到这个库。具体步骤取决于您的编译器/IDE。您表示您正在使用 Code::Blocks。引用给出的说明here关于如何在 Code::Blocks 中添加库(似乎 Code::Blocks 想要不带
.lib 后缀的库名称，因此名称将是 Ws2_32 ，而不是 Ws2_32.lib )。链接到此库后，您的代码将成功编译。
关于C++ 服务器-客户端 FTP 模拟，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13086888/