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C++ template


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 that creates a generic class or function. Library containers, such as iterators and algorithms, are examples of generic programming that use the concept of templates.

Each container has a single definition, such as vector, we can define many different types of vectors, such as or vector <string>

You can use templates to define functions and classes, so let's take a look at how to use them.

function template

The general form of the

template function definition is as follows:

template <class type> ret-type func-name(parameter list) { // The body of the function }

Here, type is the placeholder name for the data type used by the function. This name can be used in the function definition.

The following is an example of a function template that returns the maximum of two numbers:

example

#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

class template

As we define function templates, we can also define class templates. The general form of a generic class declaration is as follows:

template <class type> class class-name {
.
.
.
}

Here, type is a placeholder type name that can be specified when the class is instantiated. You can define multiple generic data types using a comma-separated list.

The following example defines the class Stack<>,And implement a generic method to pop the stack on the stack:

example

#include <iostream> #include <vector> #include <cstdlib> #include <string> #include <stdexcept> using namespace std; template <class T> class Stack { private: vector<T> elems; // element public: void push(T const&); // Push into the stack void pop(); // Popping T top() const; // Return to the top element of the stack bool empty() const{ // Returns true if it is empty. return elems.empty(); } }; template <class T> void Stack<T>::push (T const& elem) { // Append a copy of the incoming element elems.push_back(elem); } template <class T> void Stack<T>::pop () { if (elems.empty()) { throw out_of_range("Stack<>::pop(): empty stack"); } // Delete the last element elems.pop_back(); } template <class T> T Stack<T>::top () const { if (elems.empty()) { throw out_of_range("Stack<>::top(): empty stack"); } // Return a copy of the last element return elems.back(); } int main() { try { Stack<int> intStack; // int Type stack Stack<string> stringStack; // string Type stack // Manipulating the stack of type int intStack.push(7); cout << intStack.top() <<endl; // Operation string type stack stringStack.push("hello"); cout << stringStack.top() << std::endl; stringStack.pop(); stringStack.pop(); } catch (exception const& ex) { cerr << "Exception: " << ex.what() <<endl; return -1; } }

When the above code is compiled and executed, it produces the following results:

7
hello
Exception: Stack<>::pop(): empty stack