Generic Programming Templates in C++/

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- Examples

- Examples

Let's check out the examples of template arguments.

We'll cover the following...

Example 1: Deduction of Template Arguments

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// templateArgumentDeduction.cpp
#include <iostream>
template <typename T>
bool isSmaller(T fir, T sec){
  return fir < sec;
}
template <typename T, typename U>
bool isSmaller2(T fir, U sec){
  return fir < sec;
}
template <typename R, typename T, typename U>
R add(T fir, U sec){
  return fir + sec;
}
int main(){
  std::cout << std::boolalpha << std::endl;
  std::cout << "isSmaller(1,2): " << isSmaller(1,2) << std::endl;
  // std::cout << "isSmaller(1,5LL): "  << isSmaller(1,5LL) << std::endl; // ERROR
  std::cout << "isSmaller<int>(1,5LL): " << isSmaller<int>(1,5LL) << std::endl;
  std::cout << "isSmaller<double>(1,5LL): " << isSmaller<double>(1,5LL) << std::endl;
  std::cout << std::endl;
  std::cout << "isSmaller2(1,5LL): "  << isSmaller2(1,5LL) << std::endl;
  std::cout << std::endl;
  std::cout << "add<long long int>(1000000,1000000): " << add<long long int>(1000000, 1000000) << std::endl;
  std::cout << "add<double,double>(1000000,1000000): " << add<double,double>(1000000, 1000000) << std::endl;
  std::cout << "add<double,double,float>(1000000,1000000): " << add<double,double,float>(1000000, 1000000) << std::endl;
  std::cout << std::endl;
}

Explanation

In the above example, we have defined 3 function templates

  • isSmaller takes two arguments which have the same type and returns true if the first element is less than the second element (line 6). Invoking the function with arguments of different types would give a compile-time error (line 25).
  • isSmaller2 takes two arguments which can have a different type. The function returns true if the first element is less than the second element (line 11).
  • add takes two arguments which can have different types (line 16). The return type must be specified because it cannot be deduced from the function arguments.

Example 2: Template Default Arguments

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// templateDefaultArgument.cpp
#include <functional>
#include <iostream>
#include <string>
class Account{
public:
  explicit Account(double b): balance(b){}
  double getBalance() const {
    return balance;
  }
private:
  double balance;
};
template <typename T, typename Pred= std::less<T> >
bool isSmaller(T fir, T sec, Pred pred= Pred() ){
  return pred(fir,sec);
}
int main(){
  std::cout << std::boolalpha << std::endl;
  std::cout << "isSmaller(3,4): " << isSmaller(3,4) << std::endl;
  std::cout << "isSmaller(2.14,3.14): "  << isSmaller(2.14,3.14) << std::endl;
  std::cout << "isSmaller(std::string(abc),std::string(def)): " << isSmaller(std::string("abc"),std::string("def")) << std::endl;
  bool resAcc= isSmaller(Account(100.0),Account(200.0),[](const Account& fir, const Account& sec){ return fir.getBalance() < sec.getBalance();});
  std::cout << "isSmaller(Account(100.0),Account(200.0)): " << resAcc << std::endl;
  bool acc= isSmaller(std::string("3.14"),std::string("2.14"),[](const std::string& fir, const std::string& sec){ return std::stod(fir) < std::stod(sec);});
  std::cout << "isSmaller(std::string(3.14),std::string(2.14)): " << acc << std::endl;
  std::cout << std::endl;
}
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