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Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
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undefined reference to typeinfo - C++ error message

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)

Commentatorsays ...
Radha:This really helped me..I wasted a lot of time over that error.
(comment added 2006-07-19 07:00:03)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
C234 - C and C based languages - Further C++ Object Oriented features
  [801] Simple polymorphism example - C++ - (2006-07-14)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [1159] It can take more that one plus one to get two. - (2007-04-22)
  [1819] Calling base class constructors - (2008-10-03)
  [2004] Variable Scope in C++ - (2009-01-22)
  [2005] Variables and pointers and references - C and C++ - (2009-01-23)
  [2576] What does const mean? C and C++ - (2010-01-15)
  [2673] Multiple Inheritance in C++ - a complete example - (2010-03-12)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2849] What are C++ references? Why use them? - (2010-07-02)
  [3057] Lots of things to do with and within a C++ class - (2010-11-16)
  [3069] Strings, Garbage Collection and Variable Scope in C++ - (2010-11-25)
  [3124] C++ - putting the language elements together into a program - (2011-01-08)
  [3238] Bradshaw, Ben and Bill. And some C and C++ pointers and references too. - (2011-04-09)
  [3430] Sigils - the characters on the start of variable names in Perl, Ruby and Fortran - (2011-09-10)
  [3509] Operator Overloading, Exceptions, Pointers, References and Templates in C++ - new examples from our courses - (2011-11-06)
  [3982] Using a vector within an object - C++ - (2013-01-19)
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [4377] Designing a base class and subclasses, and their extension, in C++ - (2015-01-01)
  [4559] When do I use the this keyword in C++? - (2015-10-29)


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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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Comment: "Had exactly the same problem, with an abstract class, one ..."
Visitor Ranking 5.0 (5=excellent, 1=poor)
1 unpublished comment pending on this page

Comment by Jonas Baeklund (published 2011-02-18)
Had exactly the same problem, with an abstract class, one method missed the =0 [#3884]

Comment by Anon (published 2011-01-16)
Phew. Exact the same problem here. Thanks for the solution. [#3862]

Comment by Anon (published 2010-10-25)
Quickly and easily solved my problem. Thanks Much. [#3809]

Comment by Anon (published 2010-10-08)
You just saved me a lot of time with this page! It was indeed an obscure error message and I appreciate your clear and helpful explanation about what I needed to fix. [Also, your mentioning how weird the error message itself seems made me feel less foolish about having no idea what it was trying to tell me!] Many thanks. [#3802]

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