Does the program become slow if I define variable in a loop?

[ImLazy]

For example, this code:

Code: Select all

for (int i = 0; i < 100; i++) {
    int a = i;
    f(a);
}

Will the variable "a" be allocated 100 times? Or it is allocated at the beginning of the loop and destroyed when the loop finishes?

[Darko]

Interesting - I just tried both versions (declared inside and outside) and they compile in exactly the same way. (gcc 3.4.3)

Well, I just printed a inside the loop, I don't know what would happen if you do something more complicated.

Darko

[Krzysztof Duleba]

This is because static variables are not really "allocated". Static variable is just an address on stack that is chosen during compilation.

[Moha]

These is no diffrence in running time. But the C++ draft suggest us to declare variable inside the loop as much as possible. and that is why C++ compiler can optimize on memory. And You should know that in C/C++ local variable alocated in stack, but sometimes there is some cost of changeing between memory farmes. So declaring a variable inside a loop is much easier and safer.