question about pointers

This is a discussion on question about pointers within the C++ Programming forums, part of the General Programming Boards category; if i had int y, x; const int *ptr=&y; can i assign ptr = &x;...

  1. #1
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    question about pointers

    if i had

    int y, x;
    const int *ptr=&y;

    can i assign

    ptr = &x;
    Last edited by kuwait; 12-14-2002 at 04:07 PM.
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  2. #2
    Confused Magos's Avatar
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    Yes. The pointer points to a (const int). It's not the pointer that is constant.
    And you can have a const XXX pointer point at XXX (since something read and writable can be assumed only readable) but you cannot have a XXX pointer point at const XXX, since the pointer would allow you to write to something that is unwritable.
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    thanx for answering

    another question

    will x be constant in this case?
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  4. #4
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    Originally posted by kuwait
    thanx for answering

    another question

    will x be constant in this case?
    Sure, but it depends on which way you look at it. ptr promises not to change x, but if you had another pointer pointing to x (non-const) you could change it (or even just change x directly).

    for example:

    int x = 32;
    const int *cptr = &x;
    int *ptr = &x;

    (*ptr)++; // Legal
    (*cptr)++; // Illegal, cptr promises not to change the data it point to


    Edit: Also worth mentioning that you can specify const pointers; using your first example, we can make it illegal to change what ptr points to, as well as make it illegal to change the data it points to.

    int x,y;
    const int * const ptr = &x;

    ptr = &y; // Illegal, ptr is const
    Last edited by Eibro; 12-14-2002 at 05:47 PM.

  5. #5
    Just a Member ammar's Avatar
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    the pointer is const not x, x can be changed but not by that pointer.
    none...

  6. #6
    Programming Sex-God Polymorphic OOP's Avatar
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    if you want the pointer itself to be constant, then put const after the asterisk, IE

    int* const ptr = &x;

    ptr = &y; // ERROR: ptr is a constant

    you can also do

    const int* const ptr = &x;

    which is a constant pointer to a constant int

  7. #7
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