Use of "for (;;)" in a C# application?

Question

I've been looking through some sample source code for an application I use and I came across this line:

for (;;)
{
// The rest of the application's code
}

It looks like this is to create an infinite loop, but I'm not familiar with ";;" and it's very hard to Google unfortunately.

Solution 1

Yes, that is an infinite loop. It's an ordinary for loop with no condition expression.

From the documentation for for:

All of the expressions of the for statement are optional; for example, the following statement is used to write an infinite loop:

for (; ; )
{
    // ...
}

Solution 2

I just want to clarify :

;; is not a special operator or something - it's a regular for loop.

regular for loop looks like that:

for (do_before_loop**;** finish_loop_when_this_condition_is_false**;** do_after_each_iteration);

if you leave all 3 parts empty you get ;; - and since you don't have an exit condition - this is an infinite loop.

Solution 3

Normally You write Your loop like this:

for (int i = 0; i < 10; i++)
{
// The rest of the application's code
}

Now, when You want Your loop to be infinite one, You just have to remove the "int i = 0", condition "i < 10", and incrementation "i++". If You do this, then in a for statement You will see only ";;"

for (;;)
{
// The rest of the application's code
}

Solution 4

Yes, it's an infinite loop.

All parameters in the for statement are optional, and the condition defaults to true, so it's the same as:

for (;true;)

or:

while (true)

Solution 5

This is the same as for (<initial>; <condition>; <increment>), you're simply leaving out initial, condition and increment. In this case, condition will always be considered true.

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Comments

[JuniorDeveloper1208]

Thanks, is it common practice (IE: Not a hack?)

[Richard J. Ross III]

One thing to note is that you should have a condition on which to break from it, to have a non-ending loop is usually bad... @toleero, it is a matter of style. I like to use the while (true) {} loop instead, it is more straight to the point IMO, but either one is standard practice.

[Oded]

@t84 - Fairly common, though many use while(true){} for readability.

[Guffa]

@toleero: It's not a hack, but it has a slight smell to it... You should try to put the condition in the loop statement if practically possible, instead of breaking out of the loop.

[T.E.D.]

@toleero - I don't know about C#, but in C and C++, that is the cannocical way to do an infinite loop.

[Malcolm Tucker]

Technically, for the loop to be infinite, all you have to remove is the condition (i<10).