C++ Coding Standard

Rule: CFL#025

Synopsis:	Use a reference to a range based loop "auto" variable if it is modified in its body
Language:	C++
Severity Level:	2
Category:	Control Flow

Description:

Consider the following code

  std::vector<int> ints{ 10, 20, 30 };
  for(auto i : ints) {
    if (i == 30) {
      i = 40; 
    }
  }
  do something with "ints"

Then after the for loop the "ints" variable will still be unchanged! Instead a reference to the "auto" variable should be used:

  std::vector<int> ints{ 10, 20, 30 };
  for(auto& i : ints) {
    if (i == 30) {
      i = 40; 
    }
  }
  do something with "ints"

Literature References: