How much memory does malloc(0) allocate?

Discussion in 'C Programming' started by Lynn McGuire, Jul 26, 2013.

  1. Lynn McGuire

    BGB Guest

    well, there is a problem:
    often the size of these integer types is relevant for things like
    file-formats, and often for memory use.

    there is actually lots of code which will break at present if 'int' is
    anything other than 32 bits.

    but, OTOH, sometimes one may need to deal with arrays larger than 2 or
    4G on 64-bit targets, and it is still mostly overkill for characters.


    also annoying is the still not yet universal availability of 'stdint.h', ...


    then there are other annoyances:
    there is still no good way to have 'specific' format integer types, for
    example:
    "32-bit signed twos complement big-endian" or "64-bit unsigned twos
    complement little-endian".

    as-is, the majority of code for reading/writing data from files often
    ends up with code for jerking around with getting numbers into the
    correct endianess, where if the exactly format of the numbers was
    settled, a person could safely read/write structs more directly, and not
    need a bunch of logic for encoding/decoding any contained integers.

    but, even if added to the standards, it would probably be a decade or
    more before it had widespread implementation support, ...

    so, alas, no good solutions to the problems of integers.


    FWIW: in my scripting language, it is possible to qualify the endianess
    of integer types, but made partly pointless in that I don't generally
    use it for file IO (and the VM still falls a fair bit short of being
    performance competitive with a C compiler, *1). nevermind some still
    ugly language-design issues (*2), ...

    *1: the current JIT also mostly just spits out threaded code, and the
    current IR still isn't really ideal for what is needed for good
    performance (mostly it is a time/priority issue).

    *2: ugly AS3-like declaration syntax, semantics issues, sometimes
    excessive verbosity, ...


    or such...
     
    BGB, Jul 30, 2013
    #61
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  2. Lynn McGuire

    Ian Collins Guest

    There speaks someone who has never worked in the embedded world (most C
    these days) or on drivers or any other in memory data applications.
     
    Ian Collins, Jul 30, 2013
    #62
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  3. I was talking about what C has, not what it should have.

    I disagree with your point, but even if I agreed it would still be a bad
    idea to confuse the terms "int" and "integer".
     
    Keith Thompson, Jul 30, 2013
    #63
  4. (snip)
    So, for the real question, does C require size_t to
    be unsigned?

    For 32 bit systems with 24 or 31 bit addressing, it could just as
    well be signed and still address (or size) everything.

    Many systems with 32 bit addresses save enough addressing space
    for the OS, such that user space could be sized in 31 bits.

    -- glen
     
    glen herrmannsfeldt, Jul 30, 2013
    #64
  5. Lynn McGuire

    James Kuyper Guest

    Yes:
    "The header <stddef.h> defines the following macros and declares the
    following types.
    ....
    size_t

    which is the unsigned integer type of the result of the sizeof
    operator;" 7.19p1-2
     
    James Kuyper, Jul 30, 2013
    #65
  6. Lynn McGuire

    Phil Carmody Guest

    Let's start with clearly defined or otherwise unambiguous terms, and
    see if we can progress from there.

    Phil
     
    Phil Carmody, Aug 1, 2013
    #66
  7. Probably better style but not required.
    I'd bet he meant the clear and visible abort() caused by a failed
    assert() -- often with a coredump or somesuch -- instead of continuing
    without error indication or at most a warning which people ignore.
    This is often called fail-fast or fail-hard.
     
    David Thompson, Aug 5, 2013
    #67
  8. Lynn McGuire

    Eric Sosman Guest

    For his purpose (to wit: Treating an attempted zero-length
    allocation as an assertion failure), it's required.
     
    Eric Sosman, Aug 5, 2013
    #68
  9. Lynn McGuire

    Kleuske Guest

    Thank you.
     
    Kleuske, Aug 5, 2013
    #69
  10. Lynn McGuire

    Kleuske Guest

    Correct, apart from the "he"-issue (still female last time i checked). I
    considered that implied, but if you want to state that explicitly, that's
    fine, too.

    Addendum: It does no make much of a difference, but it is nicer not to
    allocate first and assert() afterwards. "Required", therefore, is a bit
    strong, but i would certainly not accept it in a code review.
     
    Kleuske, Aug 6, 2013
    #70
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