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C++ Fundamentals for Professionals

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Explore C++ function and class templates through practical examples. Understand template argument deduction, default template parameters, and how automatic return type deduction works to enhance your programming skills.

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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 example above, 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
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