C++11 range based loop: How does it really work

Question

I know how this loop works, and how I can use it in practical problems. But I want to know what is happening under the hood. I thought that this loop was similar to a regular for loop in which for example

for(int i = 0 ; i < 5 ; i ++){
    // instructions
}

Variable i is initialized only once, so I thought that this was the same for range based loops. But if I for example write this code:

for(const int x : vec) {
    cout << x << endl;
}

The compiler lets me to do this, but I don't understand how this is possible. If variable x is const, how come in every iteration the x value is different?

Answer 1

Every iteration of the loop creates a local variable x and initializes it to the next element of vec. When the loop iteration ends, x goes out of scope. A single x is never modified.

See this link for the precise semantics.