Can someone tell me if an IF statement checks a group of conditions individually and breaks from the statement intelligently? If it does then it would surely be better to phrase this line (which has to evaluate every AND): if (this && this && this && this && this) { // code for first condition } like this (which quits after the first condition is FALSE): if (this) { if (this) { if (this) { // code for first condition } } } If that's the case, then what about this statement: if (!this || !this || !this || !this || !this) { // code for other condition } How could you optimise this, if the IF does not quit after the first !this test fails? Which way does it work? Paulcoz. Edited by - paulcoz on March 6, 2001 7:04:41 PM

A decent compiler will drop out as soon as possible (VC++ 6 does). It also depends on the programming language, I think JAVA is specified to drop out as early as poss.

BReaks at the first False.

AND breaks at the first false as said above. I believe they are evaluated left to right, so put your least expensive tests first.

OR breaks at the first true. So, once again, I believe you should place your least expensive tests first.

It''s true that they''re evaluated left-to-right, which allows you to do things like:

if( pObject && pObject->IsReady() )
{
}



IsReady() isn''t called if pObject is NULL.

~CGameProgrammer( );

While reading the Topic "Simple question about IFs, ANDs, ORs" I discovered this weird quirk of C++ 9or maybe just the compiler)

using namespace std;class Object{ public: bool IsReady() { return true; }};int main(){ Object* p = NULL; if(!p && p->IsReady()) { } return 0;}

p->IsReady() should cause an access violation because p is a pointer to NULL. Unfortunately (or fortunately?) because Object''s IsReady method is declared inline, p->IsReady() is replaced by the compiler with the inline code.

Should this be considered a bug?



Dire Wolf
www.digitalfiends.com

paulcoz, like everyone has said, C/C++ will quit evaulating stuff the first chance it gets. For a series of and''s this means when you hit the first false. For a series of or''s it would be the first true.

This behavior is called "short-circuiting" and I think it''s in the language spec. Not all languages do this.

-Mike