There are some compiler and loader error messages that shout obviously as to their cause, but there are others that simply don't give the new user much of an indication as to what's really wrong. And most of those I get to know pretty quickly, so that I can whip around a room during a course, making suggestions to delegate to check for missing ; characters or double quotes, to check that they have used the right type of brackets for a list subscript and haven't unintentionally written a function call, etc.

Here's one of the more obscure messages from the Gnu C++ compiler - or rather from the loader:

g++ -o polygon shape.o circle.o square.o polygon.o
circle.o(.gnu.linkonce.r._ZTI6Circle+0x8): undefined reference to `typeinfo for Shape'
square.o(.gnu.linkonce.r._ZTI6Square+0x8): undefined reference to `typeinfo for Shape'
polygon.o(.gnu.linkonce.t._ZN5ShapeC2Ev+0x8): In function `Shape::Shape()':
: undefined reference to `vtable for Shape'
collect2: ld returned 1 exit status


And you can be scratching you head for hour over that one!

The error? shape.o contains a base class from which classes are derived in circle.o and square.o .. but virtual function(s) in shape's definition are missing null bodies.

The fix? You've got line(s) like
virtual float getarea() ;
that should read
virtual float getarea() {} ;

The complete (working) source code files for this example are available here
(written 2006-07-15, updated 2008-05-04)

Commentator	says ...
Radha:	This really helped me..I wasted a lot of time over that error. (comment added 2006-07-19 07:00:03)

C234 - C and C based languages - Further C++ Object Oriented features
  [3509] Operator Overloading, Exceptions, Pointers, References and Templates in C++ - new examples from our courses - (2011-11-06)
  [3430] Sigils - the characters on the start of variable names in Perl, Ruby and Fortran - (2011-09-10)
  [3238] Bradshaw, Ben and Bill. And some C and C++ pointers and references too. - (2011-04-09)
  [3124] C++ - putting the language elements together into a program - (2011-01-08)
  [3069] Strings, Garbage Collection and Variable Scope in C++ - (2010-11-25)
  [3057] Lots of things to do with and within a C++ class - (2010-11-16)
  [2849] What are C++ references? Why use them? - (2010-07-02)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2673] Multiple Inheritance in C++ - a complete example - (2010-03-12)
  [2576] What does const mean? C and C++ - (2010-01-15)
  [2005] Variables and pointers and references - C and C++ - (2009-01-23)
  [2004] Variable Scope in C++ - (2009-01-22)
  [1819] Calling base class constructors - (2008-10-03)
  [1159] It can take more that one plus one to get two. - (2007-04-22)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [801] Simple polymorphism example - C++ - (2006-07-14)

Back to Simple polymorphism example - C++

Previous and next or Horse's mouth home

Forward to Not shouting

Check your user is human. Have him retype a word in a graphic
Melksham Carnival Parade
The Courts, Holt
Not shouting
undefined reference to typeinfo - C++ error message
Effective web campaign?
The case for exceptions
References and Pointers in C++
Writing up new C / C++ notes.