NULL of no type~

This is a discussion on NULL of no type~ within the C++ Programming forums, part of the General Programming Boards category; howdy~ i used to consider NULL as general var for any type but nowdays found some problems occured when i ...

  1. #1
    flashing vampire black's Avatar
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    NULL of no type~

    howdy~

    i used to consider NULL as general var for any type but nowdays found some problems occured when i did this in my class implementation, ie a method called "find" which purpose is to search the list specifed for certain value and return the position found or NULL otherwise. but when i return NULL my compiler report an error which said there was a type mismatch, which meant we cant return NULL as another type. so what can we do when we want NULL can be returned and satisfy any type ?

    note: finde method return a template type so it will only be defiend when run-time comes.
    Never end on learning~

  2. #2
    vae victus! skorman00's Avatar
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    you should only return NULL if you're returning a pointer. If not, returning NULL doesnt make sense.

  3. #3
    Registered User jlou's Avatar
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    Some ideas:
    • Change the return type to a pointer so that you can return null.
    • Add a parameter to the function in which the found item will be placed, and return a bool indicating whether the find was successful.
    • Throw an exception if a failed search is an exceptional situation.
    • Identify a value for the type that acts as a not found (e.g. -1 or 0 for integers). This isn't so easy if you return a template type. This can also be done like the STL does it - the user can check the returned position against the position one past the end of the list.
    I like the second or fourth idea best.

  4. #4
    flashing vampire black's Avatar
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    Quote Originally Posted by jlou
    Some ideas:
    • Change the return type to a pointer so that you can return null.
    • Add a parameter to the function in which the found item will be placed, and return a bool indicating whether the find was successful.
    • Throw an exception if a failed search is an exceptional situation.
    • Identify a value for the type that acts as a not found (e.g. -1 or 0 for integers). This isn't so easy if you return a template type. This can also be done like the STL does it - the user can check the returned position against the position one past the end of the list.
    I like the second or fourth idea best.
    thanx man i think second one makes sense. but it seems there is still conflicts if we use another parameter to store the found item, how to declare its data type when implements it ? because it would be of a template type(if found) or NULL(not found).
    Never end on learning~

  5. #5
    Registered User jlou's Avatar
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    If you take in a reference as the position output parameter, then instead of setting it to NULL when the search fails you just leave the value unchanged. It is up to the user of your list to check the return value of the function for true or false before using the position.

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