Loop performance for local variable

Question

Is there any performance penalties has 1st sample vs. 2nd one and why?

// 1. variable is declared inside the loop body
while(isSomethingTrue == true) {
  std::string str;
  findStr(str); // str initialization
  processStr(str); // processStr does not change its argument
}

// 2. variable is declared outside the loop body
std::string str;
while(isSomethingTrue == true) {
  findStr(str);
  processStr(str);
}

Answer 1

In general there will be the overhead of running the constructor/deconstructor of your object per loop iteration, if it isn't plain old data. In case of string: allocating and deallocating str's internal buffer. This only impacts performance if findStr and processStr are both highly performant too.