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Re: sizeof(x) / sizeof(x[0])

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Alla _ wrote:
> Hello!
>
> Please, read my explanation before answering, to show
> my mistake.
> Honestly, for some time now I was sure I have no problems
> with the statement sizeof(x) / sizeof(x[0]), usually used as
> the macro to compute the size of an array of strings. I was
> positive that I know how it works, and didn't doubt.
> Somehow today when I used this macro again I've experienced
> a confusion - how does it work, and what have I completely
> forgotten? Although shameful, I have decided to come here again
> for help on this matter.
>
> For example:
> char *array[] = {"abc", "defg", "hijklmop", NULL};
> The pointer points to an array that has 4 strings.
> sizeof(x) here will be sizeof(array) thus indicating
> the size in bytes of the whole array of strings,
> because 'array' here is used as the address of the
> first sub-element, which is 'a' (array is the same as
> array[0][0]);
>
> so sizeof(array) will give the number of bytes occupied
> by the whole array of strings, i.e. number
> of characters x 1 (which is the size of a char);
>


Assume 4-byte pointers.

sizeof(array) is then 16 - 4*4.
sizeof(array[0]) is 4
sizeof(array[0][0]) is 1 - sizeof(char)

> the denominator sizeof(x[0]) gives the size of the
> first element of the array, i.e. the size of the first
> string, which is here "abc", so it it is 3 (3 characters,

C strings don't really have a size, they have a length.

A char array that contains a string may have a size, but
the way you've declared things the size is lost information.

So if you can get to a debugger or write a dump routine. look
at how things are laid out in memory and all will be revealed.

> each 1 byte); and all other strings have different
> number of characters in them, and hence different
> number of bytes;
>

You can get to the length of each string by using strlen().

> how then sizeof(x) / sizeof(x[0]) gives a correct number
> of strings in the array (it actually does, I have tested it
> on different strings)? Please, show me my mistake.
>
> Thank you!
>

l
-- 
Les Cargill

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sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-14 04:16 -0800
  Re: sizeof(x) / sizeof(x[0]) "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-14 04:27 -0800
    Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-14 04:43 -0800
      Re: sizeof(x) / sizeof(x[0]) "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-14 04:52 -0800
        Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-14 06:10 -0800
        Re: sizeof(x) / sizeof(x[0]) Keith Thompson <kst-u@mib.org> - 2017-01-14 15:55 -0800
  Re: sizeof(x) / sizeof(x[0]) jt@toerring.de (Jens Thoms Toerring) - 2017-01-14 13:13 +0000
    Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-15 22:23 -0800
      Re: sizeof(x) / sizeof(x[0]) Keith Thompson <kst-u@mib.org> - 2017-01-16 08:58 -0800
  Re: sizeof(x) / sizeof(x[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-14 14:47 +0000
    Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-14 07:17 -0800
  Re: sizeof(x) / sizeof(x[0]) Manfred <noname@invalid.add> - 2017-01-14 16:22 +0100
  Re: sizeof(x) / sizeof(x[0]) Barry Schwarz <schwarzb@dqel.com> - 2017-01-14 08:35 -0800
    Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-15 22:53 -0800
      Re: sizeof(x) / sizeof(x[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-16 15:58 +0000
        Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-16 22:38 -0800
          Re: sizeof(x) / sizeof(x[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-17 10:11 +0000
  Re: sizeof(x) / sizeof(x[0]) James Kuyper <jameskuyper@verizon.net> - 2017-01-14 11:43 -0500
    Re: sizeof(x) / sizeof(x[0]) Keith Thompson <kst-u@mib.org> - 2017-01-14 16:01 -0800
    Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-16 01:36 -0800
      Re: sizeof(x) / sizeof(x[0]) Barry Schwarz <schwarzb@dqel.com> - 2017-01-16 09:47 -0800
      Re: sizeof(x) / sizeof(x[0]) James Kuyper <jameskuyper@verizon.net> - 2017-01-16 21:12 -0500
        Re: sizeof(x) / sizeof(x[0]) Alla _ <modelling.data@gmail.com> - 2017-01-16 22:29 -0800
  Re: sizeof(x) / sizeof(x[0]) Les Cargill <lcargill99@comcast.com> - 2017-01-14 14:27 -0600
  Re: sizeof(x) / sizeof(x[0]) Keith Thompson <kst-u@mib.org> - 2017-01-14 15:52 -0800
  Re: sizeof(x) / sizeof(x[0]) Lőrinczy Zsigmond <nospam@for.me> - 2017-01-15 20:20 +0100
    Re: sizeof(x) / sizeof(x[0]) Keith Thompson <kst-u@mib.org> - 2017-01-15 12:55 -0800

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