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C++ Fundamentals for Professionals

Functions and Function Objects

Explore how functions and function objects work in C++. Understand their role as callables, including stateful behavior and usage in algorithms. Learn about predefined function objects for arithmetic, comparison, logical, and bitwise operations to modify container behavior effectively.

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Functions

Functions are the simplest callables. They can have, apart from static variables, no state. Because the definition of a function is often widely separated from its use or even in a different translation unit, the compiler has fewer opportunities to optimize the resulting code.

C++
#include <iostream>
#include <vector>
#include <algorithm>
void square(int& i) { i = i * i; }
int main(){
  std::vector<int> myVec{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  std::for_each(myVec.begin(), myVec.end(), square);
  for (auto v: myVec) std::cout << v << " ";      // 1 4 9 16 25 36 49 64 81 100
  return 0;
}

The code above takes squares for each of the values in the given set by using std::for_each algorithm.

Function objects

At first, don’t call them functors. That’s a well-defined term from the category theory.

Function objects are objects ...