Question about include problems

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I include the header file, it says cannot find the function definition,
but when I include the cpp file, it works,
why...

in A.h

C++

#ifndef A_H
#define A_H

#include <stdlib.h>

class A{
  int member1;
 public:
  void Assign(int v);
  void Print();
};

#endif

in A.cpp

C++

#include "A.h"
#include <iostream>

using namespace std;

void A::Assign(int v){
  member1 = v;
}
void A::Print(){
  cout<<member1<<endl;
}

in main.cpp

C++

#include <stdlib.h>
#include "A.h";

int main(){
  A a1;
  a1.Assign(1);
  a1.Print();
  return 0;

error:
in main.cpp: undefined ref to A::Assign...

Thanks

Posted 21-Feb-13 11:20am

zhaoyilong1

Updated 21-Feb-13 20:14pm

v2

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4 solutions

Solution 1

All correct. Well, included <stdlib.h> it totally redundant. You should not have this error. Maybe the files are actually different, or some files are not actually included in project, or something. The files themselves are correct. Well, try to recreate the project from scratch (with such files, don't use precompiled headers) accurately, with the same exact content; it will work.

—SA

Posted 21-Feb-13 11:41am

Sergey Alexandrovich Kryukov

Comments

zhaoyilong1 22-Feb-13 2:14am

it can actually find the function, but says theres no definition of it~...

Sergey Alexandrovich Kryukov 22-Feb-13 11:29am

You do have the definition. This is tiny code, and the problem can be only in project structure/options. It compiles if you do it right. Start over, make sure you understand each step; and use the code you already have. Ask a question is you don't understand some steps...
—SA

Solution 2

In Main.cpp, try using #include "A.h", not #include <A.h>.
Cheers
Andi

Posted 21-Feb-13 11:52am

Andreas Gieriet

Comments

zhaoyilong1 22-Feb-13 2:12am

oh. that's a typo. I did the right thing there, but it is not working ~ However when I include A.cpp rather than A.h, it all works...... it makes no sense to me now.

Solution 3

Have you included A.cpp in you project. Looks like the linker is complaining that it doesn't find the definition of A::Assign.

You should give us the exact error message that you are receiving. That could show if my assumption is true.

Posted 21-Feb-13 20:20pm

nv3

Comments

enhzflep 22-Feb-13 2:22am

exactly! That's where "undefined reference" comes from - the linker.

zhaoyilong1 22-Feb-13 2:43am

yea ~ I forgot to include a.cpp into makefile

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parths · Accepted Answer · 2013-02-21T20:23:00

Solution 4

How are you compiling your project?
If you're using an IDE, did you ensure that A.cpp is added to the project?
If you're compiling from the command line or a makefile, did you ensure you added both main.cpp and A.cpp as dependencies for the output executable?

Posted 21-Feb-13 20:23pm

parths

v2

Comments

zhaoyilong1 22-Feb-13 2:42am

yeayea ,,,, I forgot to compile a.cpp in my makefile ...