The concept and significance of function template in the 56th lesson

1. divergence Problem: A method of several exchange variables in C + +

(1) macro code block VS function

Exchange of "programming experiment" variables

#include <iostream>#include<string>using namespacestd;//macro Definition code block#defineSWAP (T, a, B) Do{T C=A; A=b; b=C; } while(0);//define function ModevoidSwap (int& A,int&b) {    intc =A; A=b; b=C;}voidSwap (Double& A,Double&b) {    Doublec =A; A=b; b=C;}voidSwap (string& A,string&b) {    stringc =A; A=b; b=C;}intMain () {intA =0; intb =1;   Swap (A, b); //Swap (int&, int&)cout<<"A ="<< a <<Endl; cout<<"B ="<< b <<Endl; SWAP (int, A, b);//Macro Codecout<<"A ="<< a <<Endl; cout<<"B ="<< b <<Endl; Doublem =2; Doublen =3;  Swap (M, n); //Swap (double&, double&)cout <<"m ="<< m <<Endl; cout<<"n ="<< N <<Endl; SWAP (Double, M, n);//Macro Codecout <<"m ="<< m <<Endl; cout<<"n ="<< N <<Endl; strings ="Santa"; stringc ="Claus";        Swap (S, c); cout<<"s ="<< s <<Endl; cout<<"C ="<< C <<Endl; SWAP (string, S, c); cout<<"s ="<< s <<Endl; cout<<"C ="<< C <<Endl; return 0;}

(2) Comparison of advantages and disadvantages

	Hong Yihong code block	Defining functions
Advantages	code reuse for all types	A real function call , the compiler checks the type
Disadvantages	compiler does not know the existence of macros, missing type checking	Duplicate a function by type, cannot code reuse

2. New Solution-Generic programming

(1) Regardless of the specific data types of programming, the combination of the advantages of the above two scenarios.

(2) function template: Generics in C + +

① a special function can be called with different types

② looks similar to normal functions, except that types can be parameterized , such as

Template<typename t>

void Swap (t& A, t& B)

(3) Syntax rules for function templates

The ①template keyword is used to declare the beginning of generic programming

②TypeName keyword for declaring a generic type

3. Use of function templates

(1) automatic type deduction call

int a = 0, b = 1;

Swap (A, b); Automatic derivation

(2) Explicit invocation of a specific type

float c = 2, d = 3;

Swap<float> (c, D); Explicitly called

On the use of "programming experiment" function template

#include <iostream>#include<string>using namespacestd;template<typename t>voidSwap (t& A, t&b) {T C=A; A=b; b=C;} Template<typename t>voidSelectsort (T a[],intLen) {     for(inti =0; i < Len; i++)    {         for(intj = i; J < Len; J + +)        {            if(A[i] < a[j])//Descending{Swap (a[i], a[j]); }}}}template<typename t>voidPrintln (T a[],intLen) {     for(inti =0; i < Len; i++) {cout<< A[i] <<", "; } cout<<Endl;}intMain () {inta[5] = {5,3,2,4,1}; Println (A,5); Selectsort (A,5); Println (A,5); strings[5] = {"Java","C + +","Pascal","Ruby","Basic"}; Println (s),5); Selectsort (s),5); Println (s),5); return 0;}

4. Summary

(1) function template is one of the ways that generic programming is applied in C + +

(2) function template can deduce parameter types based on actual parameters

(3) Function templates support explicitly specifying parameter types

(4) Function template is an important method of code reuse in C + +

The concept and significance of function template in the 56th lesson