Templates

Templates 

Advantages of templates:

• Code reuse
• Allows container classes (e.g. lists, arrays, etc.) to be simply defined without loss of static type checking or run-time efficiency.
• Allows definition of generic functions (e.g., sort) to be defined once for a family of types

Function template and template function:

• Function templates are used to implement an entire range of related(overloaded) functions.
• When the actual parameter is substituted in the template the process is called instantiating the function template and each instantiated version is called a template function. i.e. template function is a specific instance of function template.

Class templates and template class:

• Class templates are used to implement an entire range of related classes.
• Template class is the instantiation with the type argument.

 Auto_ptr:

• Auto_ptr is a template class and is initialized with a pointer and can be derefenced in the way a pointer can.
• Auto_ptr supports resource acquisition is initialization technique.
• Auto_ptr has ownership semantics or destructive copy semantics: When an auto_ptr is copied into another, the source no longer points to anything.
• Copying a auto_ptr modifies it – a const auto_ptr cannot be copied.
• The purpose of the auto_ptr scheme is that dynamically allocated objects are properly destroyed in all circumstances i.e. the object’s destructor is properly executed.
• Template specification of auto_ptr:

template

class auto_ptr

{

public:

        typedef T element_type;

        explicit auto_ptr(T *p = 0) throw();

        auto_ptr(const auto_ptr& rhs) throw();

        auto_ptr& operator=(auto_ptr& rhs) throw();

        ~auto_ptr();

        T& operator*() const throw();

        T *operator->() const throw();

        T *get() const throw();

        T *release() const throw();

};

Example:

#include

#include

using namespace std;

class X

{

public:

X() { cout << “X::X()\n” ;}

~X() { cout << “X::~X()\n” ;}

void f() { cout << “X::f()\n”; }

};

int main()

{

auto_ptr p1(new X), p2;

p2 = p1;       // ownership transfer

p2->f();

X *ptr = p2.get();

ptr ->f();

return 0;

}

Result:

X::X()

X::f()

X::f()

X::~X()         (Destructor called when scope ends)