Question

My project is to write a program in C++ that creates a user-defined, list-implemented stack and queue that checks for letter-by-letter palindromes and word-by-word palindromes. So I would need to have a stack and queue that checks for char and string types. Since it’s a project for intermediate programming (third course in my C++ sequence), we can’t use the STL list/queue/stack objects, and we haven’t learned templates yet. But I figure it’s annoying to have to write a different implementation for string or char input and want to use templates.

I got the program to run just fine when all the code is under a single file – the classes and their implementations are all in my main.cpp. But I split the code up, putting the class definitions in a list.h and the implementation in a list.cpp, and kept the driver code in main.cpp.

Now when I run, I get these errors:

Error   1   error LNK2019: unresolved external symbol "public: void __thiscall  Stack<int>::push_front(int)" (?push_front@?$Stack@H@@QAEXH@Z) referenced in function _main  
Error   3   error LNK2019: unresolved external symbol "public: void __thiscall Queue<char>::push_back(char)" (?push_back@?$Queue@D@@QAEXD@Z) referenced in function _main   d:\my documents\visual studio 2012\Projects\DACUNTO_HW5P2_TEMP\DACUNTO_HW5P2_TEMP\main.obj  DACUNTO_HW5P2_TEMP
Error   2   error LNK2019: unresolved external symbol "public: int __thiscall Stack<int>::pop_front(void)" (?pop_front@?$Stack@H@@QAEHXZ) referenced in function _main  d:\my documents\visual studio 2012\Projects\DACUNTO_HW5P2_TEMP\DACUNTO_HW5P2_TEMP\main.obj  DACUNTO_HW5P2_TEMP
Error   4   error LNK2019: unresolved external symbol "public: char __thiscall Queue<char>::pop_back(void)" (?pop_back@?$Queue@D@@QAEDXZ) referenced in function _main  d:\my documents\visual studio 2012\Projects\DACUNTO_HW5P2_TEMP\DACUNTO_HW5P2_TEMP\main.obj  DACUNTO_HW5P2_TEMP
Error   5   error LNK1120: 4 unresolved externals   d:\my documents\visual studio 2012\Projects\DACUNTO_HW5P2_TEMP\Debug\DACUNTO_HW5P2_TEMP.exe 1   1   DACUNTO_HW5P2_TEMP

I don’t know why this happens, but the program runs fine when it’s all under one file. Here’s my code:

main.cpp: http://pastebin.com/mQW4EV99

list.h: http://pastebin.com/Lze6jZv2

list.cpp: http://pastebin.com/7bks6Bt1

Thank you

Answer 1

The compiler wants the templates’ definitions visible where used.

Either:

• Move the definitions to the class declaration (e.g. similar to your constructor for List)
• or #include the .cpp (and change its extension for your sanity)

When you hear templates can increase compile times, this is the primary reason why.