Including header files in C++ (class definition and method implementation)

Question

I have already checked StackOverflow to find the solution to my problem, but I think I might be missing something. I am trying to define a class in a header file (.h) and implement its methods in a cpp file (.cpp), but it does not work.

main.cpp:

#include <iostream> #include "Message.h" using namespace std; int main() { Message *t = new (Message); t->display(); return 0; }

Message.h:

#ifndef MESSAGE_H_INCLUDED #define MESSAGE_H_INCLUDED class Message { public: void display(); }; #endif // MESSAGE_H_INCLUDED

Message.cpp:

#include "Message.h" void Message::display() { cout << "Hello!"; }

I don't understand why I keep getting the following error

undefined reference to 'Message::display()'

Your code is correct (aside from the memory leak). Message.cpp is not getting linked - possibly not compiled. — Drew Dormann
– Drew Dormann, Commented Aug 15, 2015 at 22:24
I am using CodeBlocks (GNU GCC Compiler), with the flags: -O2, -ansi, -Wall and -pedantic — Vinícius Lopes Simões
– Vinícius Lopes Simões, Commented Aug 15, 2015 at 22:29
CodeBlocks will show you the compilation command being run. Show us, please. — Drew Dormann
– Drew Dormann, Commented Aug 15, 2015 at 22:34
Thank you, I just fixed it. It was a compiling error, I solved it by going through Project->Properties...->Build Targets and then selecting all the files in the bottom section! — Vinícius Lopes Simões
– Vinícius Lopes Simões, Commented Aug 15, 2015 at 22:39

user4386938 · Accepted Answer · 2015-08-15 22:41:23Z

2

Compile this with the command g++ -std=c++11 Message.cpp main.cpp

answered Aug 15, 2015 at 22:41

user4386938

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