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C++: ? operator

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It''s more of an alternative to using a if/else block for example (using the example above)

if(a == 2)
{
x = 3;
}
else
{
x = 5
}


as you can see the ?: operator is a lot more concise an also allows you to achieve the equivalent of an if/else block on return statements:



bool SomeFunc(void)
{
int *Ptr = NULL;
//blah

return ((Ptr == NULL) ? false, true);
}


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quote:
Original post by Spudder

return ((Ptr == NULL) ? false, true);


That''s the perfect example on how to NOT use the ternary operator. This line should be:

return( Ptr != NULL );

The ternary operator is usually used as a shortcut to an if/else or switch block, if an assignment is based on a selection. For example:

*( isBoxFilled ? DrawFilledBox : DrawEmptyBox )(Coords, Color);

Instead of

if( isBoxFilled )
DrawFilledBox(Coords, Color);
else
DrawEmptyBox(Coords, Color);

Or perhaps:

color buttonColor = ( alert > 0 ) ? colorRed : colorGray;

It''s shorter, and more readable.

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I wasn''t saying that was the best way to use the ?: operator, but it was the first example i could think of which demonstrated how ?: could represent an if/else block in a situation when you can''t actually use one which hopefully explained some of the benefits as when i was first starting out with C++ i couldn''t quite see the advantage of ?:

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quote:
Original post by Spudder
I wasn''t saying that was the best way to use the ?: operator, but it was the first example i could think of which demonstrated how ?: could represent an if/else block in a situation when you can''t actually use one which hopefully explained some of the benefits as when i was first starting out with C++ i couldn''t quite see the advantage of ?:


Well, the problem was not so much the use of ?: in itself, but the fact that your :? returned a boolean value. A ?: returning a bool simply doesn''t make sense, as the input of ?: is already a boolean.

These two:

bool b = a ? true : false;
bool c = a ? false : true;

are totally equal to

bool b = a;
bool c = !a;


A statement such as

return ((Ptr == NULL) ? false : true);

is valid C/C++, and will work, but it is redundant and meaningless. The ?: basically becomes a NO-OP, since the result is already available in the condition itself. Just as, for example

if( v == 2 ) v = 2;


So generally speaking, returning a bool from a ?: works fine, but it''s bad style. It won''t give any additional functionality, but make your code more difficult to read, and obfuscated.

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A good place to use the ternary operator is in an intializer list of a class constructor:


class Happy
{
Happy(int i, int j) : m_happy(i>5?5:i), m_joy(j<10?10:j)
{}
//...

};







--{You fight like a dairy farmer!}

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quote:
Original post by ALX
Well, the problem was not so much the use of ?: in itself, but the fact that your :? returned a boolean value. A ?: returning a bool simply doesn''t make sense, as the input of ?: is already a boolean.


Plus, he used a comma (,) instead of a colon (...it shouldn''t even compile

Regards,
Jeff






[ CodeDread ]

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