Item 14 in 'Effective C++'

[Bart Vandewoestyne]

I'm trying to run one of the examples from item 14 in Scott Meyer's Effective C++ book. As suggested in the book, I already made the EnemyTarget destructor virtual, so I assume the code should compile and run just fine. This is what I have:

https://github.com/BartVandewoestyne/cpp/tree/master/books/Effective_C++/item14

I'm compiling with g++ 4.6.2 and get:

$ g++ main.cpp
/tmp/ccOt7F5P.o: In function `EnemyTarget::EnemyTarget()':
main.cpp.gnu.linkonce.t._ZN11EnemyTargetC2Ev+0xf): undefined reference to `vtable for EnemyTarget'
/tmp/ccOt7F5P.o: In function `EnemyTank::EnemyTank()':
main.cpp.gnu.linkonce.t._ZN9EnemyTankC1Ev+0x1f): undefined reference to `vtable for EnemyTank'
main.cpp.gnu.linkonce.t._ZN9EnemyTankC1Ev+0x26): undefined reference to `EnemyTank::numTanks'
main.cpp.gnu.linkonce.t._ZN9EnemyTankC1Ev+0x31): undefined reference to `EnemyTank::numTanks'
collect2: ld returned 1 exit status

but I don't see why... I already checked the errate on Scott's website, but can't find anything that helps me forward.

What am I missing here?

Regards,
Bart

 

[Ian Collins]

I'm trying to run one of the examples from item 14 in Scott Meyer's Effective C++ book. As suggested in the book, I already made the EnemyTarget destructor virtual, so I assume the code should compile and run just fine. This is what I have:

https://github.com/BartVandewoestyne/cpp/tree/master/books/Effective_C++/item14

I'm compiling with g++ 4.6.2 and get:

$ g++ main.cpp
/tmp/ccOt7F5P.o: In function `EnemyTarget::EnemyTarget()':
main.cpp.gnu.linkonce.t._ZN11EnemyTargetC2Ev+0xf): undefined reference to `vtable for EnemyTarget'
/tmp/ccOt7F5P.o: In function `EnemyTank::EnemyTank()':
main.cpp.gnu.linkonce.t._ZN9EnemyTankC1Ev+0x1f): undefined reference to `vtable for EnemyTank'
main.cpp.gnu.linkonce.t._ZN9EnemyTankC1Ev+0x26): undefined reference to `EnemyTank::numTanks'
main.cpp.gnu.linkonce.t._ZN9EnemyTankC1Ev+0x31): undefined reference to `EnemyTank::numTanks'
collect2: ld returned 1 exit status

but I don't see why... I already checked the errate on Scott's website, but can't find anything that helps me forward.

What am I missing here?

You don't define EnemyTank::numTanks in the programme.

Do you intend to use the destroy() method?

 

[Bart Vandewoestyne]

Even before reading your answer, i figured out my 'mistakes' myself... I just love it when I find things myself! ;-)

1) You're right about EnemyTank::numTanks.

2) I also discovered that the destroy() method is virtual in both EnemyTarget and EnemyTank. The book doesn't show an implementation of it. Apparently, the fact that it's virtual in both EnemyTarget and EnemyTank is causingthe linker error. Commenting the function out in both classes makes stuffto compile.

I guess I should have been more critical about the code-example before simply brain-dead trying to compile it ;-)

Thanks!