for( ; ;)

[cdalten]

Does for( ; test for
expr !=0 or expr == 0?

Chad

[Slacker]

Well, for(;; ) is technically always true, so it doesn't matter. But in general, conditional tests by default test for != 0. That's why

if ( x ) {
  /* Stuff */
}

Executes the block if x isn't 0.

[Ancient Dragon]

probably depends on the compiler, but VC++ 2005 Express does not make any tests, it just creates an infinite loop with a jump at the bottom back to the top of the loop. No test is necessary. As if you had written this:

int main()
{
loop:
   // do some code here
   goto loop;
}

[laserlight]

The C Standard says that an "omitted expression-2 is replaced by a nonzero constant", where expression-2 refers to the expression that controls the for loop.

So you might say that it tests for expr == 1, but then the wording of the standard is effectively "leaving out expression-2 creates an infinite loop", so no comparison is actually required in the first place.