pointers

This is a discussion on pointers within the C Programming forums, part of the General Programming Boards category; Hey guys if i declare Code: int *px; does that mean px is a pointer to an int Code: float ...

  1. #1
    Musicman - Canora
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    pointers

    Hey guys if i declare

    Code:
    int *px;
    does that mean px is a pointer to an int

    Code:
    float *pa = &a;
    would that mean the address of &a is of pa which is a pointer to the float

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by bazzano View Post
    Hey guys if i declare

    Code:
    int *px;
    does that mean px is a pointer to an int
    Yes.

    Quote Originally Posted by bazzano View Post
    Code:
    float *pa = &a;
    would that mean the address of &a is of pa which is a pointer to the float
    If a is a float, then &a is the address of the float a, and in the initialization the float pointer pa would have a value of the address of a.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
    Musicman - Canora
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    how about if its this

    double *a[12] would that be a pointer to a pointer of type double because its an array

  4. #4
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by bazzano View Post
    how about if its this

    double *a[12] would that be a pointer to a pointer of type double because its an array
    a is an array of 12 pointers to double. a[0], a[1], etc. is each a pointer to double.

    A pointer to a pointer to a double is declared as double **a.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  5. #5
    Algorithm Dissector iMalc's Avatar
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    In general, the type is best understood by reading it from right to left:
    [12] an array of twelve <- * pointers <- double to doubles.
    My homepage
    Advice: Take only as directed - If symptoms persist, please see your debugger

    Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"

  6. #6
    Just Lurking Dave_Sinkula's Avatar
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    I've come to think of it as kind of a spiral from the middle.
    http://www.codeproject.com/cpp/compl...ight_left_rule
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  7. #7
    Musicman - Canora
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    So if i have

    Code:
    int [5] = {10,20,30,40,50}
    if i say
    Code:
    (x + 2)
    would that give me 30

    and if i go
    Code:
    (*x + 2)
    will that make x point to the address of 30

    but also how about if it was
    Code:
    *(x + 2)

  8. #8
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by bazzano View Post
    So if i have

    Code:
    int [5] = {10,20,30,40,50}
    if i say
    Code:
    (x + 2)
    would that give me 30

    and if i go
    Code:
    (*x + 2)
    will that make x point to the address of 30

    but also how about if it was
    Code:
    *(x + 2)
    If you have
    Code:
    int x[5] = {10,20,30,40,50}
    then
    Code:
    (x + 2)
    is the address of the int containing 30.

    If you have
    Code:
    (*x + 2)
    that would be a value of 12.

    If you have
    Code:
    *(x + 2)
    that would be the value 30.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  9. #9
    Musicman - Canora
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    Could somone elaborate more please?

  10. #10
    Just Lurking Dave_Sinkula's Avatar
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    Perhaps your compiler could.
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
       int x[5] = {10,20,30,40,50};
       int *y = (x + 2);
       int z = (*x + 2);
       int p = *(x + 2);
       printf(" y = &#37;p\n", (void*)y);
       printf("*y = %d\n", *y);
       printf(" z = %d\n",  z);
       printf(" p = %d\n",  p);
       return 0;
    }
    Sometimes you just need to look at something a couple hundred times before it is as clear as can be.

    I know I have. And there are still more than a few things on the list.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  11. #11
    Musicman - Canora
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    Thanks mate

  12. #12
    Musicman - Canora
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    pointers

    What i dont get is how you got 12 for Z

  13. #13
    CSharpener vart's Avatar
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    Quote Originally Posted by bazzano View Post
    What i dont get is how you got 12 for Z
    *x is 10
    10 + 2 is 12
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  14. #14
    Musicman - Canora
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    So does that int z = (*x+2)

    x is alread pointing to the zeroth element in the array but because its a * its getting the value of x which is 10. Then adding 2 to ten.

    And not incrementing where x is pointing too

  15. #15
    CSharpener vart's Avatar
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    Quote Originally Posted by bazzano View Post
    So does that int z = (*x+2)

    x is alread pointing to the zeroth element in the array but because its a * its getting the value of x which is 10. Then adding 2 to ten.

    And not incrementing where x is pointing too
    yes...
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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