Question

Possible Duplicate:
Is short-circuiting boolean operators mandated in C/C++? And evaluation order?

Is there any defined by standard or math rules order of eveluating boolean sentences? For example:

if (firstTrue && secondTrue)
{
}

can I be sure that firstTrue will be checked first?

Answer 1

Yes. && and || are short circuiting operators. The order of evaluation of operands is well defined (left to right).

&& is also a sequence point.
So writing if( ++i && i) { } is perfectly fine.

ISO C++03 (5.14/1) says:

The && operator groups left-to-right. The operands are both implicitly converted to type bool (clause 4). The result is true if both operands are true and false otherwise. Unlike &, && guarantees left-to-right evaluation: the second operand is not evaluated if the first operand is false.

EDIT: (After seeing the comment)

ISO C++03 (Section 1.9/18) says

In the evaluation of each of the expressions

a && b

a || b

a ? b : c

a , b

using the built-in meaning of the operators in these expressions (5.14, 5.15, 5.16, 5.18), there is a sequence point after the evaluation of the first expression.