Re: Static Arrays Inside Functions

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: Static Arrays Inside Functions
Date	2019-04-27 13:14 -0700
Organization	None to speak of
Message-ID	<ln36m3yzmc.fsf@kst-u.example.com> (permalink)
References	<qa24so02brf@news3.newsguy.com> <GP0xE.813777$%SF.591883@fx15.am4>

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Bart <bc@freeuk.com> writes:
> On 27/04/2019 18:52, F. Russell wrote:
>> I need to include a lookup table, via an array, within a library function
>> that will be linked to other C programs:
>> 
>> double some_function(...)
>> {
>> static double[100] = {55.55, 66.66, ...}

You forgot to provide a name for the array.

static double arr[100] = {55.55, 66.66, /* ... */};

The "static" keyword means that the object is created and initialized
once, during program startup.  Defining it inside a function means that
the name is visible only within the function, but the object exists and
can be accessed indirectly from anywhere (for example if the function
saves a pointer value).

>> ...
>> }
>> 
>> I am not sure when this array will actually be initialized.
>> 
>> Will the array be initialized during compile time so that the
>> function code contains the values?
>> 
>> Or will the array be initialized during the first call to the function
>> and thereafter remain static?
>
> At compile-time.

The compiler generates code that results, at run-time, in the
object being allocated and initialized before main() is invoked.
Typically a copy of the data will be included in the executable,
loaded at program startup along with the code.

> (Otherwise it wouldn't retain the same values on subsequent calls.)

In principle, the compiler could create an implicit flag so that
the initializion occurs exactly once, when the function is called
for the first time.  That would probably be conforming as long as
the visible behavior is the same, but I can't think of any good
reason to do it that way.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */

Thread

Static Arrays Inside Functions "F. Russell" <fr@random.info> - 2019-04-27 17:52 +0000
  Re: Static Arrays Inside Functions Bart <bc@freeuk.com> - 2019-04-27 19:03 +0100
    Re: Static Arrays Inside Functions Keith Thompson <kst-u@mib.org> - 2019-04-27 13:14 -0700
      Re: Static Arrays Inside Functions David Brown <david.brown@hesbynett.no> - 2019-04-28 00:10 +0200
  Re: Static Arrays Inside Functions Siri Cruise <chine.bleu@yahoo.com> - 2019-04-27 13:40 -0700
  Re: Static Arrays Inside Functions nobody@example.org (Scott) - 2019-04-28 17:26 +0000
    Re: Static Arrays Inside Functions Keith Thompson <kst-u@mib.org> - 2019-04-28 11:29 -0700
      Re: Static Arrays Inside Functions nobody@example.org (Scott) - 2019-04-29 01:17 +0000
        Re: Static Arrays Inside Functions Keith Thompson <kst-u@mib.org> - 2019-04-28 20:09 -0700
        Re: Static Arrays Inside Functions "F. Russell" <fr@random.info> - 2019-04-29 10:33 +0000
          Re: Static Arrays Inside Functions Bart <bc@freeuk.com> - 2019-04-29 11:49 +0100
          Re: Static Arrays Inside Functions Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-04-29 04:50 -0700
          Re: Static Arrays Inside Functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-04-29 17:36 +0100
          Re: Static Arrays Inside Functions Keith Thompson <kst-u@mib.org> - 2019-04-29 15:24 -0700
      Re: Static Arrays Inside Functions Ike Naar <ike@iceland.freeshell.org> - 2019-04-29 05:50 +0000
        Re: Static Arrays Inside Functions Ike Naar <ike@iceland.freeshell.org> - 2019-04-29 05:51 +0000
        Re: Static Arrays Inside Functions Keith Thompson <kst-u@mib.org> - 2019-04-29 00:04 -0700
          Re: Static Arrays Inside Functions Ike Naar <ike@iceland.freeshell.org> - 2019-04-29 15:06 +0000
    Re: Static Arrays Inside Functions Mateusz Viste <mateusz@wont.tell> - 2019-04-28 19:20 +0000
      Re: Static Arrays Inside Functions Keith Thompson <kst-u@mib.org> - 2019-04-28 13:50 -0700
  Re: Static Arrays Inside Functions James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-04-29 00:44 -0400

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