foreword

A template parameter classifies type parameters into non-type parameters. A type parameter is a parameter type name that appears in a template parameter list, followed by a class or typename. A non-type parameter is to use a constant as a parameter of a class (function) template, which can be used as a constant in a class (function) template.

1. Template parameters

A reference to a non-type template parameter, which solves part of our problem,

Floating point numbers, class objects, and strings are not allowed as non-type template parameters.
Non-type template parameters must have a compile-time confirmation result.

namespace ljh
{
    
    
 // 定义一个模板类型的静态数组
	 template<class T =int, size_t N = 10>
	 class array
	 {
    
    
	 private:
	 T _array[N];
	 size_t _size;
	 }
 }
 int main()
 {
    
    
 	ljh::array<int,100> s1;
 	ljh::array<int,70> s2;
 }

Similar to the above situation, when our two stacks need to open up different spaces, if there is no template parameter, we need to write two classes.
If it is a full default class, we also need to call ljh::array<> s1;

Template specialization

When do you need to use it?
When we implement an Is_empty function to determine whether two values are the same. However, since different types may be compared in different ways, we can use specialization at this time, or use the matching principle of templates.

template<class T>
bool Is_empty(T left,T right)
{
    
    
	cout << "hah" << endl;
	return left == right;
}
template<>//特化
bool Is_empty<char*>(char* left,char* right)
{
    
    
	return strcmp(left,right) == 0;
}
//模板的匹配原则
bool Is_empty(char* left,char* right)
{
    
    
	return strcmp(left,right) == 0;
}

int main()
{
    
    
	int left = 0;
	int right = 0;
	//cout << Is_empty(left, right)<<endl;
	char str1[] = "woaini";
	char str2[] = "woaini";
	cout<<typeid(str1).name()<<endl;
	cout << Is_empty(str1, str2) << endl;

	
	return 0;
}

Note that str1 and str2 here are essentially array names. When passing parameters, there is type conversion, so if we change the template function to the following const T& in the above parameter passing process, there will be problems with the specialized version. .

template<class T>
bool Is_empty(const T& left,const T& right)//error！
{
    
    
	cout << "hah" << endl;
	return left == right;
}
template<>
bool Is_empty<char*>(char* left,char* right)
{
    
    
	return strcmp(left,right) == 0;
}

Second, separate compilation

1. Import the library

Solution 1: Explicitly specify instantiation.
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Solution 2: Do not separate compilation. Declarations and definitions are in a .h file. Because this way, the address of his function has been confirmed when compiling.

Summarize

Template advanced is here! !

[c++] template advanced

Template advanced