Error LNK2019: unresolved external symbol...

smack1878 · #1 18-Feb-2009, 10:02

Hi, I´m new to c++ and inheritance therefore I have a problem with this code. Please help

I want to create two classes ("leaf" and "internal") that inherit from "node". I removed everything from the code to reproduced the error.
When I call a function that uses "node" in "leaf.cpp" a link error occurs :S

The error is:
Linking...
leaf.obj : error LNK2019: unresolved external symbol "public: void __thiscall node::test(class node *)" (?test@node@@QAEXPAV1@@Z) referenced in function "public: void __thiscall leaf::test(class node *)" (?test@leaf@@QAEXPAVnode@@@Z)
C:\Documents and Settings\MiguelDeVezEmQuando\My Documents\Visual Studio 2005\Projects\tree\Debug\tree.exe : fatal error LNK1120: 1 unresolved externals
Build log was saved at "file://c:\Documents and Settings\MiguelDeVezEmQuando\My Documents\Visual Studio 2005\Projects\tree\tree\Debug\BuildLog.htm"
tree - 2 error(s), 0 warning(s)

I got three ".h"s
Node.h

CPP / C++ / C Code:

 
#ifndef nodeH
#define nodeH

class node {
	public:
	node* k;
	void test(node* in);
};

#endif

Leaf.h

CPP / C++ / C Code:

 
#include "node.h"

#ifndef leafH
#define leafH

class leaf : public node {
public:
void test(node* in);
};

#endif

Internal.h

CPP / C++ / C Code:

 
#include "node.h"

#ifndef internalH
#define internalH

class internal : public node{
	public:
	node* j;
	void test(node* in);
};

#endif

And one CPP
Leaf.cpp

CPP / C++ / C Code:

 
#include "leaf.h"

#ifndef leafCPP
#define leafCPP


void leaf::test(node* in)
{
	in->test(in);
}

int main()
{
	return 0;
}

#endif

smack1878 · #2 18-Feb-2009, 11:22

The solution for this lnk2019 error is solved (Hurray) with a virtual destructor in class Node (though I dont understand why :S).

Alexandra · #3 19-Feb-2009, 06:06

For future reference, let's look at the error again. It's very informative, actually.
leaf.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall node::test(class node )"
"unresolved external symbol" basically means the linker could not find a variable or function.
And...
virtual void __thiscall node::test(class node *)
Tells us that the function in question is the member function test inside class node that takes a node as argument.

Possible reasons as to why it cannot find it is that...
1) You have a function which you forgot to implement (ie, you simply forgot or you misspelled the name).
2) Misspelled variable.
3) All source files weren't compiled properly (can sometimes happen; a rebuild will likely solve that in VS

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Error LNK2019: unresolved external symbol...

Re: inheritance problem, please help :P

Re: Error LNK2019: unresolved external symbol...