1. Templates (again)
Professor Hugh C. Lauer CS-2303, System Programming Concepts
(Slides include materials from The C Programming Language, 2nd edition, by Kernighan and Ritchie, Absolute C++, by Walter Savitch, The C++ Programming Language, Special Edition, by Bjarne Stroustrup, and from C: How to Program, 5th and 6th editions, by Deitel and Deitel)
CS-2303, A-Term 2012
Templates (again)

2. Outline Function templates and related (overloaded) functions
Distinguishing between function templates and function-template specializations
Class templates to create a group of related types
Distinguishing between class templates and class-template specializations
Overloading function templates
Relationships among templates, inheritance, friends, and static members
CS-2303, A-Term 2012
Templates (again)

3. Review — Function Templates
Written by programmer once
Defines a whole family of overloaded functions
Begins with the template keyword
Contains template parameter list of formal types
Formal type parameters
Enclosed in angle brackets (<>)
Preceded by keyword typename or keyword class
Placeholders for fundamental or user-defined types
Similar to macros in C, but with full type checking
Week 5, Miscellaneous C++ topics §16.1 of Absolute C++
CS-2303, A-Term 2012
Templates (again)

4. Software Engineering Note
Most C++ compilers require complete definition of template in client source-code using the template
 Templates often defined in header files
Included via #include into the appropriate client files
For class templates, member functions must also be defined in header file
CS-2303, A-Term 2012
Templates (again)

5. Function Template — Example Forms
Common Programming error:– Forgetting to say class or typename
template<typename T> f() { }
template<class ElementType> g(){ }
template<typename BorderType, typename Filltype> h() { }
Another common Programming error:– Forgetting to say class or typename for every parameter
CS-2303, A-Term 2012
Templates (again)

6. Common Programming Error
If template is invoked with user-defined type, and …
… if template uses functions or operators (e.g., ==, +, <=) with objects of class type, then …
… those functions and operators must be overloaded for the user-defined type
Forgetting to overload such operators causes compilation errors
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Templates (again)

7. Function Template Specialization
Definition:–
Function Template Specialization
Specialization:– the automatic generation of a new “overloaded function” from the template as needed
I.e., whenever a function template is called with a particular type
Example for function template max with type parameter T called with int arguments
Compiler detects a max invocation in the program code.
int is substituted for T throughout the template definition.
This produces function-template specialization max<int>
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Templates (again)

8. Overloading Function Templates
Other function templates that specify the same name but different parameters
Non-template functions that specify the same name but different parameters
The compiler chooses best function or specialization to match the function call
A non-template function is chosen over a template specialization in case of a tie
Otherwise, multiple matches results in a compilation error (the compiler considers the function call to be an ambiguous function call )
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Templates (again)

9. Questions about Function Templates?
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10. Class Templates Class-template definitions are preceded by a header
Also known as Parameterized Types
Class Templates
Class-template definitions are preceded by a header
Such as template< typename T >
Type parameter T can be used as data type in members functions and data
Multiple type parameters can be specified using comma-separated list – e.g.,
template< typename T1, typename T2 >
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11. Class Templates (continued)
Class templates encourage software reusability …
… by enabling type-specific versions of generic classes to be instantiated
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12. Example
Stack.h (1 of 3)
Create class template Stack with type parameter T
Member functions with type parameter T in parameter lists
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13. Example (continued) Stack.h (2 of 3)
Data member stackPtr is pointer to T
Member-function template definitions appearing outside class-template definition begin with template header
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14. Note: function bodies are spelled out in class header file!
Stack.h (3 of 3)
Note: function bodies are spelled out in class header file!
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15. T might have to overload operator =
Stack.h (3ʹ of 3)
T might have to overload operator =
Why?
Digression: What if T
is an abstract class with subclasses?
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16. Example.cpp (1 of 2) Create specialization Stack< double >
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17. Example.cpp (2 of 2) Create specialization Stack< int >
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18. Test.cpp (1 of 2)
Use a function template to process Stack class-template specializations
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19. Test.cpp (2 of 2)
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20. Questions?
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21. Non-type Parameters and Default Types for Class Templates
Nontype template parameters
Can have default arguments
Are treated as const
Example
Template header: template<typename T, int elements>... Declaration: Stack< double, 100 > salesFigures;
Type parameters can have default arguments – example:–
Template header: template< typename T = string >... Declaration: Stack<> jobDescriptions;
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22. Templates and Inheritance
A class template can be derived from a class-template specialization
A class template can be derived from a non-template class
A class-template specialization can be derived from a class-template specialization
A non-template class can be derived from a class-template specialization
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23. Templates and Friends Assume:– template<typename T> class X
A function can be a friend of every class-template specialization instantiated from a class template
friend void f1();
f1 is a friend of X<double>, X<string>, etc.
A function can be the friend of only a class-template specialization with the same type argument
friend void f2( X<T> & );
f2( X<float> & ) is a friend of X<float> but not a friend of X<string>
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Templates (again)

24. Templates and Friends (continued)
A member function of another class can be a friend of every class-template specialization instantiated from a class template
friend void A::f3();
f3 of class A is a friend of X< double >, X< string >, etc.
A member function of another class can be a friend of only a class-template specialization with the same type argument
friend void C<T>::f4( X<T> & );
C<float>::f4( X<float> & ) is a friend of X<float> but not a friend of X<string>
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Templates (again)

25. Templates and Friends (continued)
Another class can be a friend of every class-template specialization instantiated from a class template
friend class Y;
Every member function of class Y is a friend of X<double>, X<string>, etc.
A class-template specialization can be the friend of only a class-template specialization with the same type parameter
friend class Z< T >;
Class-template specialization Z<float> is a friend of X<float>, Z<string> is a friend of X<string>, etc.
CS-2303, A-Term 2012
Templates (again)

26. Templates and static members
Each class-template specialization has own copy of each static data member
All objects of that specialization share that one static data member
static data members must be defined and, if necessary, initialized at file scope
Each class-template specialization gets its own copy of the class template’s static member functions
CS-2303, A-Term 2012
Templates (again)

27. Questions about Class Templates?
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28. Templates in the C++ Standard Library
Strings
<basic_string> is the template class
string is typedef basic_string<char>
There are lots of other kinds of strings
Japanese, Chinese, w_char, etc.
Vector
Generalization of one-dimensional array
Includes (stack operations, etc.)
vector<bool> is a specialization for one bit per bool item
List
Ditto
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29. Templates in the C++ Standard Library (continued)
ValArray
bitset
Bitwise operations on bits
Iterators
For sequencing through collections of objects …
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30. Questions?
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31. CS-2303, A-Term 2012
Templates (again)