C++ 错误 LNK2001：未解析的外部符号函数 _main
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C++ error LNK2001: unresolved external symbol function _main
提问by Carlos Landeras
Possible Duplicate:
What is an undefined reference/unresolved external symbol error and how do I fix it?
I'm learning C++ and I have a compiling problem in my project. I have read tons of post with this error on the title but I cant find where the problem is.
我正在学习 C++，但我的项目中有一个编译问题。我已经阅读了大量标题上有此错误的帖子，但我找不到问题所在。
I have a method call in my Main function that is responsible for the error. Whenever I comment the line the project compiles perfect.
我的 Main 函数中有一个方法调用负责该错误。每当我评论该行时，该项目都会完美编译。
The code is the following:
代码如下：
Main.cpp
主程序
#pragma once
#include "stdafx.h"
#include <iostream>
#include <sstream>
#include <WinSock.h>
#include <Windows.h>
#include <string.h>
#include "NetUtils.h"
#include "Utils.h"
#include "FileUtils.h"
#include "SendMail.h"
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
SendMail *mail = new SendMail("[email protected]","Envio de C++","Cuerpo del mail");
char* msg="";
mail->SendNow();
...
This method mail->SendNow is the one I comment to solve the problem, so I guess I have some kind of header declaration problem inside of SendMail.cpp or SendMail.h
这个方法mail->SendNow是我评论解决问题的方法，所以我猜我在SendMail.cpp或SendMail.h内部有某种标题声明问题
Now the rest of the classes and headers:
现在剩下的类和标题：
SendMail.h
发送邮件.h
#pragma once
#ifndef SENDMAIL_H
#define SENDMAIL_H
class SendMail
{
public:
SendMail(char* c_to, char* c_subject, char* c_body);
void Check(int iStatus, char *szFunction);
void SendNow();
char * to;
char * subject;
char * body;
};
#endif
SendMail.cpp
发送邮件.cpp
#define WIN32_LEAN_AND_MEAN
#pragma once
#include "SendMail.h"
#include <stdio.h>
#include <stdlib.h>
#include <fstream>
#include <iostream>
#include <windows.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")
using namespace std;
// Insist on at least Winsock v1.1
const int VERSION_MAJOR = 1;
const int VERSION_MINOR = 1;
#define CRLF "\r\n" // carriage-return/line feed pair
SendMail::SendMail(char* c_to, char* c_subject, char* c_body)
{
to = c_to;
subject= c_subject;
body = c_body;
}
// Basic error checking for send() and recv() functions
void Check(int iStatus, char *szFunction)
{
if((iStatus != SOCKET_ERROR) && (iStatus))
return;
cerr << "Error during call to " << szFunction << ": " << iStatus << " - " << GetLastError() << endl;
}
void SendNow()
{
// WSADATA WSData;
///* Attempt to intialize WinSock (1.1 or later)*/
// if(WSAStartup(MAKEWORD(VERSION_MAJOR, VERSION_MINOR), &WSData))
// {
// cout << "Cannot find Winsock v" << VERSION_MAJOR << "." << VERSION_MINOR << " or later!" << endl;
// ErrMsg="Cannot find Winsock v";
// return;
// }
}
AS you can see the method Send is commented out so I cant figure out what the problem is.
如您所见，方法 Send 已被注释掉，因此我无法弄清楚问题是什么。
The compiler output is:
编译器输出是：
Error 6 error LNK1120: 1 unresolved externals C:\Users\clanderasm\Documents\Visual Studio 2010\Projects\LandeTestConsole\Debug\LandeCplusConsole.exe LandeCplusConsole
Error 5 error LNK2019: unresolved external symbol "public: void __thiscall SendMail::SendNow(void)" (?SendNow@SendMail@@QAEXXZ) referenced in function _main C:\Users\clanderasm\Documents\Visual Studio 2010\Projects\LandeTestConsole\LandeCplusConsole\LandeCplusConsole.obj LandeCplusConsole
回答by Jasper
Basically what that error means is that you have a function that you promise to implement in your header, but when it got to the part where it actually needed the function, it didn't find it.
基本上这个错误意味着你有一个你承诺在你的头文件中实现的函数，但是当它到达它实际需要该函数的部分时，它没有找到它。
If you comment out the function call, the promise that you will implement that function is still there. However, nobody is actually using the function, so it doesn't matter that you don't come through on your promise.
如果您注释掉函数调用，您将实现该函数的承诺仍然存在。但是，实际上没有人使用该功能，因此您不兑现承诺并不重要。
Once you know that it means, it's pretty easy to find what is wrong:
一旦你知道这意味着什么，就很容易找出问题所在：
You are defining the function as:
您将函数定义为：
void SendNow()
This is a global function and not a class function, as such you have not implemented the class function you promised to implement.
这是一个全局函数而不是类函数，因此您尚未实现您承诺实现的类函数。
You can fix this by turning it into:
您可以通过将其转换为以下内容来解决此问题：
void SendMail::SendNow()
Do note that you have the same problem in Check()even though that's not causing an error yet.
请注意，Check()即使尚未导致错误，您也遇到了同样的问题。
回答by Luchian Grigore
Did you mean
你的意思是
void SendMail::Check(int iStatus, char *szFunction)
void SendMail::SendNow()
instead of
代替
void Check(int iStatus, char *szFunction)
void SendNow()
