Template initial level template

1. Generic Programming

Write generic type independent code , Is a means of code reuse . Templates are the foundation of generic programming

2. Templates

2.1 Function templates

Concept : Function templates represent a family of functions , The function template is type independent , Parameterized when used , Generate a specific type version of the function based on the argument type , Template function .

Format :template<typename T1,typenameT2,......typename Tn>

return type Function name ( parameter list ){}

template<typename T>
void Swap( T& left, T& right) {
 T tmp = left;
 left = right;
 right = tmp; }

Function template itself is not a function , It is a tool used by the compiler to generate specific types of functions . So in fact, the template is to give the compiler the repeated things we should have done

In the compiler compilation phase , For the use of template functions , The compiler needs to deduce and generate the function of the corresponding type according to the input argument type For calling . such as ： When used double Type when using function templates , The compiler deduces the type of arguments , take T Determined as double type , however A special treatment is produced after double Type of code , The same is true for character types .

Instantiation of template function : Different types of When parameter uses function template , Called a function template Instantiation . Template parameter instantiation is divided into ： Implicit instantiation and explicit instantiation turn .

(1) Implicitly instantiate : Let the compiler deduce the actual type of template parameters according to the actual parameters

(2) Explicitly instantiate : After the function name <> Add parameter type in

(3) Matching principle of template parameters : A template function can exist simultaneously with a non template function with the same name , And this function can also be instantiated as this non template function ; For non template functions and functions with the same name , If all other conditions are the same , When transferring, priority will be given to calling non template functions instead of from this template The board produces an example . If the template can produce a function with a better match , Then the template will be selected, and the template function does not allow automatic type conversion , However, ordinary functions can perform automatic type conversion .

2.2 Class template

Format :

template<class T1, class T2, ..., class Tn>
class  Class template name 
{
 //  Definition of members within a class 
};

Functions in class templates are function templates ; 

Class template instantiation is different from function template instantiation , Class template instantiation needs to be followed by the class template name <>, Then place the instantiated type in <> Then you can , Class template name is not a real class , The result of instantiation is the real class .

template<size_t N>  Non type template parameters