Re: undefined reference(compile error), plz help

From:

Paavo Helde <myfirstname@osa.pri.ee>

Newsgroups:

comp.lang.c++

Date:

Thu, 09 Jun 2011 02:44:02 -0500

Message-ID:

<Xns9EFF6D31B8C19myfirstnameosapriee@216.196.109.131>

eric <cneric12lin0@gmail.com> wrote in news:33ca3f4e-bbef-4072-9fc6-
dec670fffaa7@x38g2000pri.googlegroups.com:

class IntArray {
public:
   // equality and inequality operations: #2b
   explicit IntArray( int size = DefaultArraySize );
   IntArray( int *array, int array_size );
   IntArray( const IntArray &rhs );

   // virtual destructor!
   virtual ~IntArray() { delete [] ia; }

   // equality and inequality operations:
   bool operator==( const IntArray& ) const;
   bool operator!=( const IntArray& ) const;

   // assignment operator: #2a
   IntArray& operator=( const IntArray& );
   int size() const { return _size; }

// we've removed the check on the index...
   virtual int& operator[](int index) { return ia[index]; }
   // int size() const; // #1
   virtual void sort(); // #4

[...]

but my compile result( errors) is
--
eric@eric-laptop:~/CppPrimer3$ g++ IntArray.cpp pg49.cpp
/tmp/ccOnEojJ.o: In function `IntArray::IntArray(int*, int)':
IntArray.cpp:(.text+0x8): undefined reference to `vtable for IntArray'

With g++ this typically means you have not provided definition of the
first non-inline virtual function in this class. As far as I can see,
this would be IntArray::Sort(). Provide a definition of this function
(and all other non-defined virtual functions) in the relevant .cpp file.

In C++ one can in principle leave out definitions for functions which are
not used, but all virtual functions are effectively "used" for populating
the vtable entries, so they must be all present in the program.

hth
Paavo