What is the lifetime and scope of the enclosed loop variable?

Question

Possible Duplicate:
What is the scope of a while and for loop?

for (int32 segNo = 0; segNo < 10; ++segNo)
{
    my_Object cm;
}

Will the constructor and destructor of object cm be called on each pass through the loop?

If so, will the destructor be called before or after the loop variable is incremented?

@bames53 Your link doesn't answer whether the variable is destroyed prior or after the increment. — Nikos C., Dec 07 '12 at 22:09

score 8 · Answer 1 · answered Dec 07 '12 at 21:37

8

Yes. And the destructor is called before the increment. I know, short answer, but that's it.

answered Dec 07 '12 at 21:37

Nikos C.

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score 6 · Answer 2 · answered Dec 07 '12 at 21:42

#include <iostream>
struct Int {
  int x;
  Int(int value):x(value){}
  bool operator<(int y)const{return x<y;}
  void increment() { std::cout << "incremented to " << ++x << "\n";}
};
struct Log {
  Log() { std::cout << "Log created\n";}
  ~Log() { std::cout << "Log destroyed\n";}
};

int main()
{
    for(Int i=0; i<3; i.increment())
    {
        Log test;
    }
}

Result:

Log created
Log destroyed
incremented to 1
Log created
Log destroyed
incremented to 2
Log created
Log destroyed
incremented to 3

score 5 · Accepted Answer · answered Dec 07 '12 at 21:39

The life of the object is inside of those curly braces.

The default constructor gets called on line 3 of your code. The destructor would be called when you get to the }. Then your loop is incremented, then the conditional is checked. If it returns true then another object is created (and the constructor called).

What is the lifetime and scope of the enclosed loop variable?

3 Answers3