typedef

This is a discussion on typedef within the C Programming forums, part of the General Programming Boards category; typdef int arr5[5]; typedef arr5 * p_arr5; typedef p_arr5 arrp10[10]; arr5 togs; p_arr5 p2; arrp10 ap; is this all typedef ...

  1. #1
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    typedef

    typdef int arr5[5];

    typedef arr5 * p_arr5;

    typedef p_arr5 arrp10[10];

    arr5 togs;

    p_arr5 p2;

    arrp10 ap;

    is this all typedef is valid? I am confuse on how to read this typedef declarations...please give me some technique how to read this kind of declarations...thanks

  2. #2
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    Think of a typedef as something that redefines the value of one thing as another. So, for example:

    Code:
    typedef int VARIABLE_TYPE;
    VARIABLE_TYPE this_is_actually_an_int;
    
    typedef std::string STRING_TYPE;
    STRING_TYPE this_is_actually_a_string;
    
    typedef int[50] INTEGER_ARRAY;
    INTEGER_ARRAY this_is_actually_an_array_of_integers;
    (Note that I don't meet the C99 standard in here, which specifies only 32 characters to define a variable as unique . . .)

    You may also think of typedefs as a search-and-replace of sorts. It replaces the second argument with the first.
    Last edited by strange; 12-09-2009 at 11:14 PM.

  3. #3
    Woof, woof! zacs7's Avatar
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    I'd say, as an alias for a pre-existing (or forward declared) type. Not value, it really has nothing to do with values.

    Just don't typedef pointers, and all is good

  4. #4
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    Quote Originally Posted by zacs7 View Post
    Just don't typedef pointers, and all is good
    Aah, words of wisdom. Now, can you please tell that to the developers of SDLNet? . . .

    Actually, typedef'ing pointers isn't too bad (IMO), as long as you don't over-do it. And as long as you give the typedef a good, pointer-sounding name . . .

  5. #5
    Woof, woof! zacs7's Avatar
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    Function pointers maybe... but otherwise it's horrible IMO

  6. #6
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    Typedefs are read just like variable definitions, except that they start with the word typedef, and what would be the variable name is instead taken to be the alias.

    Usually that means that the type comes right after typedef and before the alias, but arrays and function pointers and anything derived from those two will surround the alias.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

  7. #7
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    It is not use often ,but know the real meaning is helpful to understand the 'typedef'

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