circular referencing Linker error 2005

constexpr (3)
Hi all,

Can you please suggest how I can avoid such a linker error without moving my function some where else?

So I have 3 header files: a.hpp, b.hpp, and c.hpp. a #include b, b #includes c, c include #a. All of the header files have header guard. There is a function in b.hpp, called addition which takes 2 integers and return the sum of them. When I call the addition() in my main, it doesn't compile and throws a linker error. I would think header guard on each file would avoid the error but it just doesn't. 


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 // a.hpp

#ifndef  A_HPP
#define A_HPP

#include "b.hpp"

#endif // ! A_HPP


// b.hpp

#ifndef  B_HPP
#define B_HPP

#include <iostream>
#include "c.hpp"

int addition(int x ,int y) {return x + y;}

#endif // ! B_HPP


// c.hpp

#ifndef  C_HPP
#define C_HPP

#include "a.hpp"

#endif // ! A_HPP

// source file

#include "a.hpp"
#include <iostream>

int main() {

    std::cout << addition(10, 10);
}
highwayman (582)
Why would you make this?
salem c (3715)
No idea, works for me.
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$ for i in *.hpp *.cpp ; do  echo ===== $i ===== ; cat $i ; echo; done
===== a.hpp =====
#ifndef  A_HPP
#define A_HPP

#include "b.hpp"

#endif // ! A_HPP

===== b.hpp =====
#ifndef  B_HPP
#define B_HPP

#include <iostream>
#include "c.hpp"

int addition(int x ,int y) {return x + y;}

#endif // ! B_HPP

===== c.hpp =====
#ifndef  C_HPP
#define C_HPP

#include "a.hpp"

#endif // ! A_HPP
===== d.cpp =====
#include "a.hpp"
#include <iostream>

int main() {

    std::cout << addition(10, 10);
}
$ g++ d.cpp
$ ./a.out 
20$


And without iostream ballooning the output, the include guards do what they're supposed to.
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$ g++ -E d.cpp 
# 1 "d.cpp"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "<command-line>" 2
# 1 "d.cpp"
# 1 "a.hpp" 1



# 1 "b.hpp" 1




# 1 "c.hpp" 1



# 1 "a.hpp" 1
# 5 "c.hpp" 2
# 6 "b.hpp" 2

int addition(int x ,int y) {return x + y;}
# 5 "a.hpp" 2
# 2 "d.cpp" 2


int main() {

    std::cout << addition(10, 10);
}


constexpr (3)
//highwayman

It's from my school project. We were given a solution that already has codes in, and we need to extend it to complete some tasks. Some header files directly or indirectly include each other.


//salem c

Thank you for testing this. I run my codes on visual studio and it doesn't compile.
Last edited on
Enoizat (1343)
Just out of curiosity, could you please tell us if Visual Studio accepts this structure?

a.hpp:
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#ifndef A_HPP
#define A_HPP


#include "b.hpp"


#endif // ! A_HPP


b.hpp:
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#ifndef B_HPP
#define B_HPP


#include "c.hpp"


int addition(int x, int y);


#endif // ! B_HPP


b.cpp:
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#include "b.hpp"


int addition(int x, int y)
{
    return x + y;
}


c.hpp
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#ifndef C_HPP
#define C_HPP


#include "a.hpp"


#endif // ! C_HPP


main.cpp
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#include "a.hpp"
#include <iostream>

int main() {

    std::cout << addition(10, 10);
}

constexpr (3)
// Enoizat

It worked! Could you please explain why?
Enoizat (1343)
I don't have Visual Studio, so I don't know exactly why :-) but it's a good habit to put the function prototypes into the headers and the definitions into the 'source' files.
Maybe Visual Studio is set to consider it more an obligation than a habit (just an hypothesis).
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