why does this compile (c++)

[TecHNooB]

if(function(a),false)
{
}

I made a boo boo and wrote that instead of

if(function(a, false))
{
}

I've done this a few times actually :|

 

[Cogman]

Whatever function you are using has been overloaded as

type function(type a, bool b)

and

type function(type a)

 

[TecHNooB]

Whatever function you are using has been overloaded as

type function(type a, bool b)

and

type function(type a)

what about the comma false part in the if statement.

 

[Cogman]

http://www.cplusplus.com/forum/general/22745/

 

[Merad]

The comma is an operator. You basically wrote

if(operator,(function(a), false))

I'm a little rusty but IIRC it typically returns the first argument unless it's been overridden to do something else.

 

[TecHNooB]

worst operator ever!*






*until I find a use for it.

 

[mv2devnull]

for ( a=b=0; a<9; ++a, b+=5 ) ...

Okay, not the only way to iterate now, but it probably was quite expressive earlier.

 

[Markbnj]

The strict answer is that when the compiler sees...

if (expr) { }

... it evaluates expr to see if it is true, and if it is enters the conditional block of code. Your expression...

(function(a),false)

... is perfectly legal. The comma operator is used in C++ to separate expressions, so these two expressions are evaluated in order of precedence, i.e. left to right. Therefore the effect of the combined expression will be to, in order:

a) execute the function, passing a, and discarding the return value
b) return false to the if operator