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  • Confusion about pointers in c/cc

    From albert@spenarnc.xs4all.nl@21:1/5 to All on Wed Mar 13 10:20:45 2024
    In a recent thread there was a confusion about pointers
    in c/cc
    Algol 68 has
    'int' y;
    'ref' 'int' py;

    C has
    int y;
    int *py;

    This defines py as something that can be dereferenced to
    yield an int. This inside out type of definition leads to
    confusion.

    This is an example that you can compile with gcc
    ------------------- pointer.cc ------------
    #include <stdio.h>
    int main()
    {
    int y, *py;
    py=&y;
    printf("%x",py);
    }
    ----------------
    Running it reveals the address of y, or at least the 32 least
    significant bits.

    I couldn't find back the thread, but this is a separate subject
    anyway. Confirms the superiority of Forth ;-)

    Groetjes Albert
    --
    Don't praise the day before the evening. One swallow doesn't make spring.
    You must not say "hey" before you have crossed the bridge. Don't sell the
    hide of the bear until you shot it. Better one bird in the hand than ten in
    the air. First gain is a cat purring. - the Wise from Antrim -

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  • From minforth@21:1/5 to albert@spenarnc.xs4all.nl on Wed Mar 13 10:58:22 2024
    albert@spenarnc.xs4all.nl wrote:
    ------------------- pointer.cc ------------
    #include <stdio.h>
    int main()
    {
    int y, *py;
    py=&y;
    printf("%x",py);
    }
    ----------------
    Running it reveals the address of y, or at least the 32 least
    significant bits.

    use %p instead of %x

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  • From Paul Rubin@21:1/5 to albert@spenarnc.xs4all.nl on Wed Mar 13 18:23:29 2024
    albert@spenarnc.xs4all.nl writes:
    Running it reveals the address of y, or at least the 32 least
    significant bits.

    Being able to find the addresses of memory objects is considered a
    feature in C and it's used all the time in idiomatic C. In retrospect,
    other languages have usually-good ways to do without that feature, such
    as references, access types, etc. I think if you are writing an OS or standalone embedded program in Ada though, it's not unusual to have some
    low level parts of it in assembly language, that reach into the access
    types and do stuff with the addresses.

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  • From albert@spenarnc.xs4all.nl@21:1/5 to no.email@nospam.invalid on Thu Mar 14 09:23:07 2024
    In article <8734st1u9a.fsf@nightsong.com>,
    Paul Rubin <no.email@nospam.invalid> wrote:
    albert@spenarnc.xs4all.nl writes:
    Running it reveals the address of y, or at least the 32 least
    significant bits.

    Being able to find the addresses of memory objects is considered a
    feature in C and it's used all the time in idiomatic C. In retrospect,
    other languages have usually-good ways to do without that feature, such
    as references, access types, etc. I think if you are writing an OS or >standalone embedded program in Ada though, it's not unusual to have some
    low level parts of it in assembly language, that reach into the access
    types and do stuff with the addresses.

    All non-toy languages have side-effects. All i/o are side effects.
    It is impossible to do that with addresses (ports or memory) that have connection to the real world, like actuators that close valves.
    Relying on an OS only serves to hide this.

    Groetjes Albert
    --
    Don't praise the day before the evening. One swallow doesn't make spring.
    You must not say "hey" before you have crossed the bridge. Don't sell the
    hide of the bear until you shot it. Better one bird in the hand than ten in
    the air. First gain is a cat purring. - the Wise from Antrim -

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  • From Paul Rubin@21:1/5 to albert@spenarnc.xs4all.nl on Thu Mar 14 15:04:31 2024
    albert@spenarnc.xs4all.nl writes:
    All non-toy languages have side-effects. All i/o are side effects.
    It is impossible to do that with addresses (ports or memory) that have connection to the real world, like actuators that close valves.
    Relying on an OS only serves to hide this.

    I don't see what you're getting at here. It's far preferable to isolate
    the unsafe operations to a few places in the program, than to have them pervading the code base. E.g. you can't really write a garbage
    collector without dealing with memory addresses, but if the GC is part
    of a Lisp interpreter, the user's Lisp program doesn't have to be able
    to see the raw addresses.

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