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Generic Programming Templates in C++

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Explore multiple examples demonstrating template argument deduction in C++. Understand function templates accepting same or different types, default template parameters, and the effects of passing arguments by reference, universal reference, or value. This lesson builds a strong foundation in template usage and prepares you for practical template programming.

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Example 1: Deduction of Template Arguments

C++
// 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
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