C++ Class using header and implemenation files

Question

I've put together a simple C++ "Hello World" program to practice; unfortunately, upon compilation I get a few errors:

expected ')' before fName

error: prototype for 'HelloWorld::HelloWorld(std::string, std::string)' does not match any in class 'HelloWorld'

Below is my code, can anyone help me understand what I'm missing/overlooking? Thanks.

Header:

  1 #ifndef HELLOWORLD_H_ 
  2 #define HELLOWORLD_H_
  3 #include <string>
  4 
  5 class HelloWorld
  6 {
  7     public:
  8         HelloWorld();
  9         HelloWorld(string fName, string lName);
 10         ~HelloWorld();
 11 };
 12 
 13 #endif

Implementation:

  1 #include <iostream>
  2 #include <string>
  3 #include "HelloWorld.h"
  4 
  5 using namespace std;
  6 
  7 HelloWorld::HelloWorld()
  8 {
  9     cout << "Hello, anonymous!";
 10 }
 11 
 12 HelloWorld::HelloWorld(string fName, string lName)
 13 {
 14     cout << "Hello, " << fName << ' ' << lName << endl;
 15 }
 16 
 17 HelloWorld::~HelloWorld()
 18 {
 19     cout << "Goodbye..." << endl;
 20 }

Answer 1

You need to change your header file to reference std::string instead of string because they are defined inside the std namespace.

HelloWorld(std::string fName, std::string lName);

It works in your .cpp file because you specifically import this namespace. The solution however is not to import this namespace in your header file (generally speaking a bad idea in C++).

Answer 2

If the code is exactly like what you pasted into the question, the most probable cause of the error is that in the header, the compiler is not identifying what string means, as it is not a symbol in the global namespace. Try fully qualifying it:

class HelloWorld
{
//...
   HelloWorld( std::string fName, std::string lName );
};