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For example, basic_fstream<CharT,Traits> refers to the generic class template that implements input/output operations on file streams. It is usually used as fstream which is an alias for basic_fstream<char,char_traits<char>> , or, in other words, basic_fstream working on characters of type char with the default character operation set.
The C++ Standard Library provides several generic containers, functions to use and manipulate these containers, function objects, generic strings and streams (including interactive and file I/O), support for some language features, and functions for common tasks such as finding the square root of a number.
For example, a vector would have a random-access iterator, but a list only a bidirectional iterator. Iterators are the major feature that allow the generality of the STL. For example, an algorithm to reverse a sequence can be implemented using bidirectional iterators, and then the same implementation can be used on lists, vectors and deques.
Each time an object of class X is created, the constructor of counter<X> is called, incrementing both the created and alive count. Each time an object of class X is destroyed, the alive count is decremented. It is important to note that counter<X> and counter<Y> are two separate classes and this is why they will keep separate counts of Xs and Ys.
Other uses, however, include calling a constructor directly, something which the C++ language does not otherwise permit. [ 3 ] The C++ language does allow a program to call a destructor directly, and, since it is not possible to destroy the object using a delete expression, that is how one destroys an object that was constructed via a pointer ...
For example, the compiler generated destructor will destroy each sub-object (base class or member) of the object. The compiler generated functions will be public , non- virtual [ 3 ] and the copy constructor and assignment operators will receive const& parameters (and not be of the alternative legal forms ).
Any call to a class (static or constructor call), triggers the static constructor execution. Static constructors are thread safe and implement a singleton pattern. When used in a generic programming class, static constructors are called at every new generic instantiation one per type. [8]: 38 [4]: 111 Static variables are instantiated as well.
The factory method design pattern solves problems such as: How can an object's subclasses redefine its subsequent and distinct implementation? The pattern involves creation of a factory method within the superclass that defers the object's creation to a subclass's factory method.