Very basic Code Performance

Question

Possible Duplicate:
Is there a performance difference between i++ and ++i in C++?

Can anybody explain me why ++i is faster then i++ when we want to increment integer value I guess it might refer to any programming language.

Answer 1

It absolutely is not. This is such a common fallacy which somehow keeps on perpetuating.

Note that, when "i" is an object, and an assignment is being made, "i++" will invoke a copy of that object (value before ++), whereas "++i" will not. Modern compilers will not perform a copy of the object if it is not needed.

Answer 2

Let's do some (pointless) benchmarking to show that it is irrelevant:

The Test Code: (Java)

public class TestIncrement
{
    public static void main(String[] av)
    {
        int x = 0;
        int y = 0;
        long startTime;

        // Postincrement
        startTime = System.currentTimeMillis();
        while ( startTime + 1000 > System.currentTimeMillis())
        {
            x++;
        }

        // Preincrement
        startTime = System.currentTimeMillis();
        while ( startTime + 1000 > System.currentTimeMillis())
        {
            ++y;
        }

        // Output
        System.out.println("Postincrement: " + x);
        System.out.println("Preincrement: " + y);
    }
}   

And the Output:

Postincrement: 16039755
Preincrement: 16069900

Answer 3

When you have an expression like

k = i++;

k gets the old value of i before incrementation and i gets incremented. This copy creates the performance impact and is not needed with pre-incrementation. But sometimes both are not interchangeable. In this example with

k = ++i;

you will get another value for k.