为什么“for（;;）”的测试条件成功了？

Question

Insomuch as I understand "for(;;)" has no initial condition, no test condition and no increment condition, and therefore loops forever, I am curious why the test condition succeeds each loop.

Does the empty expression ";" evaluate as true in C? Or is this a special case handled by compilers?

A similar, but unrelated question .

Answer 1

This is by the definition of the for statement in the C language. 6.8.5.3/2 "The for statement":

Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a nonzero constant .

Answer 2

C language has no such thing as "empty expression". If any expression is missing from the for statement, syntactically it means that the entire expression is omitted , not that it is there, but empty.

A for loop with an omitted second expression loops forever because the specification of for statement says so. Ie it is a dedicated feature specific to for alone, not something more generic.

Additionaly (a terminological nitpick) only the second expression is really a condition . The first and the third are not really "conditions".