error: was not declared in this scope with C++ - c++

Question

I am trying to implement a simple protocol for sending emails. Till, now I implemented four commands and a server class that receives all the commands and check whether the commands are in the right order. However, when I am creating an instance of the server class, it shows an error: SMTPServer was not declared in this scope.I don't know what else to do. Any help is appreciated as I can't complete my program without solving this error.
SMTPServer header file:
#include <string>
#include <iostream>
#include "HELO.h"
using namespace std;
#ifndef HELO_H_INCLUDED
#define HELO_H_INCLUDED
class SMTPServer
{
public: SMTPServer();
private: string newMessage;
private: string newRec;
private: string newSender;
private: string newData;
// overload constructor
// public: SMTPServer(string, string, string, string);
void SMTPServer:: send(HELO h1);
};
#endif // HELO_H_INCLUDED
SMTPServer cpp
#include "SMTPServer.h"
SMTPServer::SMTPServer()
{
newMessage = NULL;
newRec = NULL;
newSender = NULL;
newData = NULL;
};
void SMTPServer:: send(HELO h1)
{
}
Main class
#include <iostream>
#include <string>
#include "SMTPServer.h"
using namespace std;
int main() {
string mes;
string rec;
string sen;
string dat;
SMTPServer test;
//cout << endl << "HELO message: " << test.send() << endl;
return 0;
}
Thanks in advance.

Answer 1

Looks to me like you've reused the include guards from HELO.h in SMTPServer.h. That is, they should be changed to something like:
#ifndef SMTPSERVER_H_INCLUDED
#define SMTPSERVER_H_INCLUDED
...
#endif
If you use the same include guards in both, only one of them can ever be included in another file. And in fact, SMTPServer.h itself includes HELO.h, so instantly makes its own content never get past the preprocessing stage.
If it's not clear yet, just read the top of SMTPServer.h:
#include <string>
#include <iostream>
#include "HELO.h"
using namespace std;
#ifndef HELO_H_INCLUDED
So we're checking if HELO_H_INCLUDED is defined. Since it just included HELO.h, and that file presumably defines HELO_H_INCLUDED, we'll always say "Yes, it is defined!". We'll never use the content of this #ifndef.

Answer 2

You can initialize string as below:
SMTPServer::SMTPServer()
{
newMessage = "";
newRec = "";
newSender = "";
newData = "";
}
Change code below:
void SMTPServer:: send(HELO h1);
to
void send(HELO h1);
Remove Semicolon after:
SMTPServer::SMTPServer()
{
newMessage = NULL;
newRec = NULL;
newSender = NULL;
newData = NULL;
};