Explore the power of C++ templates, from function and class basics to advanced features like instantiation and concepts, enhancing code flexibility, reusability, and abstraction without performance loss.

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C++17

C++20

Templates are one of the many powerful features of Modern C++ programming. And with each new C++ standard, they become more important. 

Templates provide an efficient way to make your code more flexible and reusable, this way you can avoid repeating code that would otherwise be identical except for different types. Templates also give you the ability to provide abstraction without a performance penalty.

However, templates can be difficult to apply, can be counterintuitive, and have tricky error messages.

This course gives you the necessary information to overcome these hurdles and dive into the advanced topics. You’ll visit the basics such as function and class templates, and then explore the details to templates such as instantiation and fold expressions. Our journey also includes techniques based on templates, the design, and future directions of templates such as concepts. Based on this exhaustive tour of templates, a basic understanding of C++ is sufficient to master this course.

Let’s get started!

Generic Programming Templates in C++

// templateFunctionsTemplates.cpp

#include <iostream>
#include <string>
#include <vector>

template <typename T>
void xchg(T& x, T& y){
  T t = x;
  x =y;
  y =t;
}

template <int N>
int nTimes(int n){
  return N * n;
}

int main(){

  std::cout << std::endl;

  bool t = true;
  bool f = false;
  std::cout << "(t, f):  (" << t << ", " << f << ") "<< std::endl;
  xchg(t, f);
  std::cout << "(t, f):  (" << t << ", " << f << ") "<< std::endl;

  std::cout << std::endl;

  int int2011 = 2011;
  int int2014 = 2014;
  std::cout << "(int2011, int2014):  (" << int2011 << ", " << int2014 << ") "<< std::endl;
  xchg(int2011, int2014);
  std::cout << "(int2011, int2014):  (" << int2011 << ", " << int2014 << ") "<< std::endl;

  std::cout << std::endl;

  std::string first{"first"};
  std::string second{"second"};
  std::cout << "(first, second):  (" << first << ", " << second << ") "<< std::endl;
  xchg(first, second);
  std::cout << "(first, second):  (" << first << ", " << second << ") "<< std::endl;

  std::cout << std::endl;
  std::vector<int> intVec1{1, 2, 3, 4, 5};
  std::vector<int> intVec2{5, 4, 3, 2, 1};

  std::cout << "vec1: ";
  for (auto v: intVec1)std::cout  << v << " ";
  std::cout << "\nvec2: ";
  for (auto v: intVec2)std::cout << v << " ";
  std::cout << std::endl;
  xchg(intVec1, intVec2);

  std::cout << "vec1: ";
  for (auto v: intVec1)std::cout  << v << " ";
  std::cout << "\nvec2: ";
  for (auto v: intVec2)std::cout << v << " ";
  std::cout << std::endl;


  std::cout << "\n\n";

  std::cout << "nTimes<5>(10): " << nTimes<5>(10) << std::endl;
  std::cout << "nTimes<10>(5): " << nTimes<10>(5) << std::endl;

  std::cout << std::endl;
}

## Explanation

In the example above, we've declared two function templates: `xchg` and `nTimes` in lines 8 and 15. `xchg` swaps the values passed as arguments. The only non-type, we use is `N` in the function templates `nTimes`. `nTimes` returns the `N` times of the number passed `n`.  We have initialized multiple instances to check for functions in lines 31 and 32, lines 39 and 40, and lines 46 and 47.

Let's take a look at the examples of function templates in this lesson.

Introduction

Basics

Details

Techniques

Design

Future

Conclusion

- Examples