What does “for(;;)” mean?

Question

In C/C++, what does the following mean?

for(;;){
    ...
}

Answer 1

In C and C++ (and quite a few other languages as well), the for loop has three sections:

• a pre-loop section, which executes before the loop starts;
• an iteration condition section which, while true, will execute the body of the loop; and
• a post-iteration section which is executed after each iteration of the loop body.

For example:

for (i = 1, accum = 0; i <= 10; i++)
    accum += i;

will add up the numbers from 1 to 10 inclusive.

It's roughly equivalent to the following:

i = 1;
accum = 0;
while (i <= 10) {
    accum += i;
    i++;
}

However, nothing requires that the sections in a for statement actually contain anything and, if the iteration condition is missing, it's assumed to be true.

So the for(;;) loop basically just means:

• don't do any loop setup;
• loop forever (breaks, returns and so forth notwithstanding); and
• don't do any post-iteration processing.

In other words, it's an infinite loop.