关于for循环的问题

wawxdyy

for( ; ; )和for( ; 1 ; )都可以实现无限循环，能说下为什么可以这么用吗，尤其前者，谢谢！

Edengundam

标准规定.
C99解释:
1 The statement
for ( clause-1 ; expression-2 ; expression-3 ) statement
behaves as follows: The expression expression-2 is the controlling expression that is evaluated before each execution of the loop body. The expression expression-3 is
evaluated as a void expression after each execution of the loop body. If clause-1 is a declaration, the scope of any variables it declares is the remainder of the declaration and the entire loop, including the other two expressions; it is reached in the order of execution before the first evaluation of the controlling expression. If clause-1 is an expression, it is evaluated as a void expression before the first evaluation of the controlling expression.
2 Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a nonzero constant.

wawxdyy

谢谢