May 11, 2021 C++
Templates are the foundation of generic programming, which writes code in a way that is independent of any particular type.
A template is a blueprint or formula for creating a generic class or function. Library containers, such as iterators and algorithms, are examples of generic programming, and they all use the concept of templates.
Each container has a single definition, such as vector, and we can define many different types of vectors, such as vectors.
You can use templates to define functions and classes, so let's take a look at how to use them.
The general form of a template function definition is as follows:
template <typename type> ret-type func-name(parameter list) { // 函数的主体 }
Here, type is the placeholder name of the data type used by the function. This name can be used in function definitions.
The following is an example of a function template that returns the maximum of two numbers:
#include <iostream>
#include <string>
using namespace std;
template <typename T>
inline T const& Max (T const& a, T const& b)
{
return a < b ? b:a;
}
int main ()
{
int i = 39;
int j = 20;
cout << "Max(i, j): " << Max(i, j) << endl;
double f1 = 13.5;
double f2 = 20.7;
cout << "Max(f1, f2): " << Max(f1, f2) << endl;
string s1 = "Hello";
string s2 = "World";
cout << "Max(s1, s2): " << Max(s1, s2) << endl;
return 0;
}
When the above code is compiled and executed, it produces the following results:
Max(i, j): 39 Max(f1, f2): 20.7 Max(s1, s2): World
Just as we define function templates, we can also define class templates. Generic class declarations are generally described as follows:
template <class type> class class-name { . . . }
Here, type is the placeholder type name that can be specified when the class is instantiated. You can use a comma-separated list to define multiple generic data types.
The following example defines the class Stack and implements a generic approach to stacking elements out of the stack:
#include <iostream>
#include <vector>
#include <cstdlib>
#include <string>
#include <stdexcept>
using namespace std;
template <class T>
class Stack {
private:
vector<T> elems; // 元素
public:
void push(T const&); // 入栈
void pop(); // 出栈
T top() const; // 返回栈顶元素
bool empty() const{ // 如果为空则返回真。
return elems.empty();
}
};
template <class T>
void Stack<T>::push (T const& elem)
{
// 追加传入元素的副本
elems.push_back(elem);
}
template <class T>
void Stack<T>::pop ()
{
if (elems.empty()) {
throw out_of_range("Stack<>::pop(): empty stack");
}
// 删除最后一个元素
elems.pop_back();
}
template <class T>
T Stack<T>::top () const
{
if (elems.empty()) {
throw out_of_range("Stack<>::top(): empty stack");
}
// 返回最后一个元素的副本
return elems.back();
}
int main()
{
try {
Stack<int> intStack; // int 类型的栈
Stack<string> stringStack; // string 类型的栈
// 操作 int 类型的栈
intStack.push(7);
cout << intStack.top() <<endl;
// 操作 string 类型的栈
stringStack.push("hello");
cout << stringStack.top() << std::endl;
stringStack.pop();
stringStack.pop();
}
catch (exception const& ex) {
cout << "Exception: " << ex.what() <<endl;
}
}
When the above code is compiled and executed, it produces the following results:
7 hello Exception: Stack<>::pop(): empty stack