c++ undefined symbol when compiling

Question

FIXED: had the method twice in the header file

I get the following error when trying to compile my project

% make
g++ -o p4 testTree.o tree.o node.o check.o
Undefined                       first referenced
 symbol                             in file
Tree::inTree(int)                   tree.o
ld: fatal: Symbol referencing errors. No output written to p4
collect2: ld returned 1 exit status
*** Error code 1
make: Fatal error: Command failed for target `p4'

Makefile

p4: testTree.o tree.o node.o check.o
    g++ -o p4 testTree.o tree.o node.o check.o
testTree.o: testTree.cc tree.h node.h check.h
    g++ -c -Wall -Werror testTree.cc

tree.o: tree.h tree.cc node.h check.h
    g++ -c -Wall -Werror tree.cc
node.o: node.h node.cc check.h
    g++ -c -Wall -Werror node.cc
check.o: check.h check.cc
    g++ -c -Wall -Werror check.cc
clean:
    rm -f *~ *.o p4

Relevant code from tree.cc and tree.h:

tree.cc

...
bool Tree::inTree(int k) const
{
     return locate(k,root) != NULL;
}
...

tree.h

#ifndef TREE_H
#define TREE_H

#include "node.h"
#include "check.h"
using namespace std;
class Tree
{
  private:
    Node *root;
  public:
    Tree();
    Tree(const Tree & t);
    const Tree & operator=(const Tree &t);
    friend ostream & operator<<(ostream &out, const Tree &t);
    bool inTree(int k) const;
    double & operator[](int k);
    double & operator[](int k) const;
    ~Tree();
    bool inTree(int index);
  private:
    Node * locate(int k, Node *rt) const;
    ostream & display(ostream &out, Node *r, int dir=Node::L) const;
    void add(int k, Node*&r);
    void kill(Node *&rt);
    void copy(Node *rt, Node *&newRt);
};
#endif

I get the feeling that it's something really simple, but I can't seem to figure it out.

Why is inTree declaraed twice in the .h file? :v (One const and one non-const) — user123, Mar 18 '13 at 21:00
Yup, that was the error. Thanks a bunch. That's what I get for copying function declarations from one file to another... — LucienK, Mar 18 '13 at 21:03
Happens all the time, except in my case, it's usually entire classes :p — user123, Mar 18 '13 at 21:03

Andy Prowl · Accepted Answer · 2013-03-18T21:04:11.830

15

The message you are getting actually comes from the linker, not from the compiler.

One of your member functions, bool Tree::inTree(int index);, is correctly declared and defined as a const member function:

 // Declaration in tree.h
 bool inTree(int index) const;

 // Definition in tree.cc
 bool Tree::inTree(int k) const
 //                       ^^^^^

However, in tree.h you also define this non-const overload of inTree():

// Declaration in tree.h, definition (supposedly) nowhere
bool Tree::inTree(int k)

For which no definition is provided. This is what the linker complains about.

edited Mar 18 '13 at 21:04

answered Mar 18 '13 at 20:58

Andy Prowl

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I had it declared twice, once with (int k), once with (int index). Thanks for the help. – LucienK Mar 18 '13 at 21:05
1

@Dazedy: The problem is **not** that you declared it twice with different argument names. Argument names are irrelevant. The problem is that in one case you used the `const` qualifier, and in the other you didn't. – Andy Prowl Mar 18 '13 at 21:06
huh. so without that const, would it just overload depending on the variable name, rather than just the number/type of parameters? – LucienK Mar 18 '13 at 21:13
@Dazedy: No, you would have two declarations of the exact same member function - and the compiler would reject it. Parameter names are irrelevant, only parameter *types* determine a function's signature. – Andy Prowl Mar 18 '13 at 21:15

score 7 · Answer 2 · answered Mar 18 '13 at 20:59

7

Here is your error:

bool Tree::inTree(int k) const
{
 return locate(k,root) != NULL;
}

in your .h you define

bool inTree(int);

This is a difference!

answered Mar 18 '13 at 20:59

bash.d

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c++ undefined symbol when compiling

2 Answers2