What's a link error?

What does this mean?

I keep getting

Link error : Undefined symbol: ??.........

http://msdn.microsoft.com/library/de...d_Warnings.asp

ok, so how do I fix this?

we would need the code, at least a bit of code to determnine where the problem is...

deleted

i just looked over the code but everything seams ok.......let me try it on my compiler......

You need to define your AminoAcidAnalyzer and Element constructors. Even if they're empty, the linker requires that they be defined somewhere, which they aren't as is.

-Prelude

The linker is what matches function calls to declaractions in different units. An undefined symbol or unresolved external happens if a function definition is not found.

1: You need to #include the corresponding .cpp file at the bottom of a .h file. aminoacid_analyzyer.cpp is never included into the program, so the funtion defined therein is never defined for your main() to use it.

2: Its is generally bad practice for an implementation file to include things. move all the #includes in aminoacid_analyzer.cpp into the top of aminoacid_analyzer.h. That way you know from the interface what includes a header needs.

3: If element is part of the implementation of aminoacid_analyzer, you can safely remove the #include for it in your main program. If you use them as two distinct concrete types, then best to leave it as is.

4: I find it is helpful to explicitly define blank constructors. Some compilers might handle this for you, but it is good practice, and tells users that it is intentional, and not a work in progress.

So, in short:

remove all includes from the top of aminoacid_analyzer.cpp, and place <iostream> and "element.h" at the top of aminoacid_analyzer.h.

add an #include "aminoacid_analyzer.cpp" to the bottom of aminoacid_analyzer.h

remove the include from the top of element.h (element does not need aminoacid to work, you got it the other way round)

remove the include to element.h from the top of your main file. (unless used as a concrete type)

Imperito, I followed what you said but now aminoacid_analyzer.cpp does not recognize the class from aminoacid_analyzer.h

Did you put the #include "aminoacid_analyzer.cpp" line at the bottom of the .h file, just above the #endif? Also, make sure that you include the .h in your main file, not the .cpp.

[EDIT]
Also, as prelude mentioned, define your constructors. If this does not help, post your source again.
[/EDIT]

Here is what I got now. The error is "unknowed identifier 'AminoAcidAnalyzer'

Also, I'm not sure if I need to pass a acidCount as a parameter in the constructor?

aminoacid_main.cpp

Code:

---

#include "aminoacid_analyzer.h"
//#include "element.h"

int main( void )
{
        char elementFile[] = "elements.dat";
       
        AminoAcidAnalyzer *aaa = new AminoAcidAnalyzer;
       
        aaa->populate(elementFile);
       
        return 0;
}

---

aminoacid_analyzer.cpp

Code:

---

//#include <iostream.h>
//#include "aminoacid_analyzer.h"

AminoAcidAnalyzer::AminoAcidAnalyzer()
{
        acidCount = 0;
}

void AminoAcidAnalyzer::populate(char *elementFile)
{
        cout<<"It's Working!";
}

---

aminoacid_analyzer.h

Code:

---

#ifndef _AMINO_ACID_ANALYZER_
#define _AMINO_ACID_ANALYZER_

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

class AminoAcidAnalyzer
{
        Element elements[5];
        int acidCount;
       
        public:
                AminoAcidAnalyzer();
                void populate(char * elementFile);               
};

#include "aminoacid_analyzer.cpp"

#endif

---

element.h

Code:

---

#ifndef __ELEMENT_H__
#define __ELEMENT_H__

class Element
{
        char atomic_symbol;
        double atomic_mass;
};

#endif

---

element.h
still yet to be implemented

Odd, that example compiles and runs fine for me.

First of all, no, you don't have to pass member data from a class to member functons. There is something called a *this pointer that handles that for you. Just know that any member funciton of a class has all other memeber functions and data member in scope. For this reason, it is a good idea to declare member functions const unless they need to modify data members.

As for your problem. what system/compiler do you use? Are you sure you have LFN support? What file/line number is given with the error?

Ok I bolded my errors (all in the aminoacid_analyzer.cpp file)

As for the compiler I am using Metroworks CodeWarrior Learning Edition v1.0. Don't know if it's got LFN support. I would love to use another compiler as CW is crap but my program has to work on the CW compiler at school!

Well, I'm out. That's compilant and it compiles for me. anybody got knowledge of CW know what is missing? Prelude, any thoughts?

>That's compilant and it compiles for me
Really? What compiler do you use? I get 7 errors with the code that was posted. Also make sure that you try to run the program, if all you do is compile it will go through cleanly because the linker activates after the compiler.

>Prelude, any thoughts?
Hehe :)

Try this:

Code:

---

main.cpp:

#include <iostream.h>
#include "element.h"
#include "aminoacid_analyzer.h"
#include "aminoacid_analyzer_fleshy.h"

int main( void )
{
  char elementFile[] = "elements.dat";       
  AminoAcidAnalyzer *aaa = new AminoAcidAnalyzer;       
  aaa->populate(elementFile);       
  return 0;
}

---

Code:

---

aminoacid_analyzer.h:

#ifndef AMINO_ACID_ANALYZER__
#define AMINO_ACID_ANALYZER__

class AminoAcidAnalyzer
{
  Element elements[5];
  int acidCount;       
public:
  AminoAcidAnalyzer();
  void populate(char * elementFile);               
};

#endif

---

Code:

---

aminoacid_analyzer_fleshy.h:

AminoAcidAnalyzer :: AminoAcidAnalyzer()
{
  acidCount = 0;
}

void AminoAcidAnalyzer :: populate(char *elementFile)
{
  cout<<"It's Working!";
}

---

Code:

---

element.h:

#ifndef ELEMENT_H__
#define ELEMENT_H__

class Element
{
  char atomic_symbol;
  double atomic_mass;
};

#endif

---

Notes: The double underscore prefix in your mangled names is reserved by the implementation, avoid using it. You want to avoid #include'ing headers and source files anywhere but your main driver files or you risk linkage problems due to the spaghetti effect.

Personally, I prefer to define my class methods in another header if the class is large or in the same header as the declaration if the class is small. This is mostly because I don't like to include source files as a matter of style, it keeps things simpler to follow.

-Prelude

I comped, linked, and ran all four of the second set of sources, and it sent "it's working!" to the screen. I did this on djgpp.

Also, prelude, I find it quite helpful to include files needed for a class's implemenetation in that class's header. That way, if a class needs something that the rest of the program does not, I won't forget to include it. Also, including all fiels in the main sets up dependancies between them, so you can get subtle errors if you include things in the wrong sequence.

>I find it quite helpful to include files needed for a class's
>implemenetation in that class's header.
General rules of thumb aren't written in stone. I do the same thing as well when the situation warrants it.

-Prelude

Ok I don't know what I did but I got it working now! Hopefully I can finish this program for monday. Thanks for all your help.

Prelude, I think you might be right about the double underscore prefix. That's odd because in the assignment they didn't have that.

Ok now I am trying to link the element files as well. The setAWeight function will be called from the aminoacid_analyzer but it is endefined identifier.

aminoacid_main.cpp

Code:

---

#include "aminoacid_analyzer.h"

int main( void )
{
        char elementFile[] = "elements.dat";
        char acidFile[] = "aminoacids.dat";
       
        AminoAcidAnalyzer *aaa = new AminoAcidAnalyzer;
       
        aaa->populate(elementFile, acidFile);
       
        return 0;
}

---

aminoacid_analyzer.h

Code:

---

#ifndef AMINO_ACID_ANALYZER__
#define AMINO_ACID_ANALYZER__

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

class AminoAcidAnalyzer
{
        Element elements[5];
        int acidCount;
       
        public:
                AminoAcidAnalyzer();
                void populate(char * elementFile, char * acidFile);               
               
        private:
                void populateElements(char * elementFile);
                void populateAminoAcids(char * acidFile);
};

#endif

---

aminoacid_analyzer.cpp

Code:

---

#include <iostream.h>
#include "aminoacid_analyzer.h"
//#include "element.h"

AminoAcidAnalyzer::AminoAcidAnalyzer()
{
        acidCount = 0;
}

void AminoAcidAnalyzer::populate(char *elementFile, char *acidFile)
{
        populateElements(elementFile);
        populateAminoAcids(acidFile);
}

void AminoAcidAnalyzer::populateElements(char * elementFile)
{
        setAWeight(); <--- undefined identifier
}

void AminoAcidAnalyzer::populateAminoAcids(char * acidFile)
{
        cout<<"populateAminoAcids";
}

---

element.h

Code:

---

#ifndef ELEMENT__
#define ELEMENT__

class Element
{
        char atomic_symbol;
        double atomic_mass;
       
        public:
                void setAWeight();
                void getAWeight(char * elementFile);
};

#endif

---

element.cpp

Code:

---

#include "element.h"

void Element::setAWeight()
{

}

void Element::getAWeight(char * elementFile)
{
}

---

This is getting to be an interesting project.

The problem now is that Element::setAWeight() is called from outside the class Element without qualification. You will need to call the setAWeight() member of one of your class' Element element[]'s. Remember, class AminoAcid has data members of type Element, but Element is not a nested class declaration, so only the instantiations of Element are in scope, not the member functions of Element.

So if you want to setAWeight for one of your elements, you will need to make a pub function in AminoAcid that takes an int, and have it call a member of one of it's Element objects, like this:

Code:

---

AminoAcid::Weight(int e, whatever) {
element[e]->setAWeight(whatever);
}

---

If Element is to be an implementation detail of AminoAcid, then any required functons in Element need to be made available via AminoAcid.

Hehe, you have too many more problems and I'm gonna need to retake chem 1101