What does "for(;;)" mean?

Loop until some break, exit, throw etc. statement inside the loop executes. Basically, you can think of a for loop as consisting of:

for (setup; test; advance)
    ...

If the "test" is empty it's considered to be true, and the loop keeps running. Empty "setup" and "advance" simply do nothing.

It's an infinite loop, equivalent to while(true). When no termination condition is provided, the condition defaults to false (i.e., the loop will not terminate).

An infinite loop which continues until there is a break, exit, or goto statement.

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.