int qempty(){ return(f==r)?1:0;}
In the above snippet, what does "?" mean? What can we replace it with?
+19
A:
This is commonly referred to as the conditional operator, and when used like this:
condition ? result_if_true : result_if_false
... if the condition evaluates to true, the expression evaluates to result_if_true, otherwise it evaluates to result_if_false.
It is syntactic sugar, and in this case, it can be replaced with
int qempty()
{
if(f == r)
{
return 1;
}
else
{
return 0;
}
}
Note: Some people refer to ?: it as "the ternary operator", because it is the only ternary operator (i.e. operator that takes three arguments) in the language they are using.
Daniel LeCheminant
2009-04-27 21:09:52
I think they implicitly mean "the (C++) ternary operator". What other ternary operators exist in C++?
sblom
2009-04-27 21:16:09
That's the only one in C++
Colin
2009-04-27 21:17:56
For anyone in the need of conditional love: http://www.artima.com/cppsource/foreach.html . eric niebler explains how his boost.foreach uses the conditional operator.
Johannes Schaub - litb
2009-04-27 21:25:19
In regular code, it's syntactic sugar, but it does enable you to do conditional initialization in the initialization list of the constructot.
JohnMcG
2009-04-28 03:11:58
@JohnMcG wait, what? Could you give an example?
Tim Snowhite
2010-09-10 17:09:52
Foo(Bar* y) pMember (y == NULL ? NULL : y->pMember) -- Here, we initialize pMember to y's pMember, or NULL if it's not there. Can't put if-else in a constructor initialization, so ternary operator makes it possible.
JohnMcG
2010-09-12 12:38:20
+2
A:
It's the conditional operator.
a ? b : c
It's a shortcut for IF/THEN/ELSE.
means: if a is true, return b, else return c. In this case, if f==r, return 1, else return 0.
Joe
2009-04-27 21:10:40
+5
A:
This is a ternary operator, it's basically an inline if statement
x ? y : z
works like
if(x) y else z
except, instead of statements you have expressions; so you can use it in the middle of a more complex statement.
It's useful for writing succinct code, but can be overused to create hard to maintain code.
Richard
2009-04-27 21:11:56
You have to be careful here; it doesn't work exactly like an if statement. While you *can* say something like int `a = x ? y : z;` you *can't* say `int a = if(x) y else z;`
Daniel LeCheminant
2009-04-27 21:30:11
worthwhile to know that there is a sequence point at the '?'. That means the following is valid: ++x ? x : y;
Johannes Schaub - litb
2009-04-27 21:32:45
@Daniel, that's what I meant by having expressions rather than statements. I probably wasn't explicit enough about the difference, so thanks for adding some clarification.
Richard
2009-04-27 21:37:53
+2
A:
It is called the conditional operator.
You can replace it with:
int qempty(){
if (f == r) return 1;
else return 0;
}
jjnguy
2009-04-27 21:12:03
A:
The question mark is the conditional operator. The code means that if f==r then 1 is returned, otherwise, return 0. The code could be rewritten as
int qempty()
{
if(f==r)
return 1;
else
return 0;
}
which is probably not the cleanest way to do it, but hopefully helps your understanding.
ssakl
2009-04-27 21:14:07