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Re: error: initializer element is not constant|

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On 09/05/2017 08:54, jak wrote:
> Il 08/05/2017 13:02, bartc ha scritto:
>> On 08/05/2017 11:18, jak wrote:
>>
>>> I would like to create an array of pointers, of pointers to strings. In
>>> this way I can have the pointers as constant and I wrote this:
>>>
>>> char *Date = "01-01-80";
>>>
>>> typedef char * ch;
>>> typedef ch * p_ch;
>>>
>>> p_ch foo[] =
>>> {
>>>   &Date,
>>>   (p_ch)&"Date"
>>> };
>>>
>>> This works but I do not know how to declare foo without using typedef.
>>
>> Those types would look like this without typedefs:
>>
>> char *  str;
>> char *  array_of_str[];
>> char ** ptr_to_str;
>> char ** array_of_ptr_to_str[];
>>
>> (The arrays will need a dimension, or need to be initialised.)
>>
>> But arrays of pointers to strings would be unusual, and be harder to
>> initialise as you can't just have "ABC", but need to set up a named
>> string: char* abc="ABC", then use &abc.
>>
>> I don't think you can apply a cast to "ABC" to get the pointer you need.
>> (Well, you can cast it, but it won't be a proper pointer to string,
>> it'll just be a string, and will crash when you apply the dereference
>> below.)
>>
>> Using the array would be harder too as you'll need an extra dereference
>> to extract the string:
>>
>>    puts(*array_of_ptr_to_str[0]);
>>
> Ok ok. Bugs have also been put in the middle. The first time I wrote the
> declaration in this way:
>
> char *Date = "01-01-80";
> char **Phrases[]
> {
>    &Date
> }
>
> and gcc gave me a lot of errors.

Not surprising as you've left out "=" after "[]", and ";" after "}". You 
should try and post exact code.

After fixing that, it seemed to compile. Date has type char*; &Date has 
type char**; Phrases has type char**[], and each element needs to be 
type char**, so &Date matches (also surprising as it looked wrong).

Then this works:

  puts(*Phrases[0]);

> But I still do not understand why the compiler does not allow me this:
>
> char *Date = NULL;
> char *Phrases[]
> {
>    "Date: ",
>    Date,
>    "\r\n"
> };
>
> In the end I'm just asking him to allocate space to write in an address
> exactly as it happens when I write NULL instead of 'Date'.

Does it say it an initialiser is not constant?

NULL is just 0.

Date requires a memory access to get the NULL stored in it. Memory 
accesses only take place at runtime.

You can make this work by putting it inside a function. But then those 
memory accesses needed to build Phrases will happen every time you call 
the function. (Maybe, you can call the function once to set up a version 
of Phrases[] which is then copied to the Phrases declared outside the 
functions.)

But it's still not clear what you're trying to achieve.

Here's a normal list of strings:

char *List1[] = {"one", "two", "three"};

Here's an indirect one (list of pointers to strings):

char *A="uno", *B="due", *C="tre";
char **List2[] = {&A, &B, &C};

And you access them like this:

  puts(List1[0]);
  puts(List1[1]);
  puts(List1[2]);

  puts(*List2[0]);
  puts(*List2[1]);
  puts(*List2[2]);

What do you want to do that is different?

-- 
Bartc

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error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-08 09:55 +0200
  Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-08 10:05 +0200
  Re: error: initializer element is not constant| Noob <root@127.0.0.1> - 2017-05-08 10:38 +0200
    Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-08 11:55 +0200
      Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-08 11:01 +0100
        Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-08 12:18 +0200
          Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-08 12:02 +0100
            Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-08 09:00 -0700
              Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-08 17:50 +0100
                Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-08 11:37 -0700
                Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-08 19:49 +0100
                Re: error: initializer element is not constant| Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-08 20:13 +0100
                Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-08 12:44 -0700
                Re: error: initializer element is not constant| scott@slp53.sl.home (Scott Lurndal) - 2017-05-08 20:24 +0000
            Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-09 09:54 +0200
              Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-09 10:15 +0200
              Re: error: initializer element is not constant| GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-05-09 12:12 +0200
              Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-09 11:47 +0100
                Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-09 19:06 +0200
                Re: error: initializer element is not constant| scott@slp53.sl.home (Scott Lurndal) - 2017-05-09 17:10 +0000
                Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-09 19:20 +0200
                Re: error: initializer element is not constant| Barry Schwarz <schwarzb@dqel.com> - 2017-05-09 10:35 -0700
                Re: error: initializer element is not constant| jak <please@nospam.tnx> - 2017-05-09 20:04 +0200
                Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-09 11:57 -0700
                Re: error: initializer element is not constant| supercat@casperkitty.com - 2017-05-09 12:50 -0700
                Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-09 12:54 -0700
                Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-09 20:15 +0100
                Re: error: initializer element is not constant| "James R. Kuyper" <jameskuyper@verizon.net> - 2017-05-09 14:13 -0400
                Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-09 11:41 -0700
              Re: error: initializer element is not constant| Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-09 12:16 +0100
              Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-09 08:11 -0700
          Re: error: initializer element is not constant| Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-08 12:12 +0100
            Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-08 13:45 +0100
              Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-08 09:04 -0700
              Re: error: initializer element is not constant| Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-08 19:53 +0100
                Re: error: initializer element is not constant| bartc <bc@freeuk.com> - 2017-05-08 20:44 +0100
                Re: error: initializer element is not constant| Noob <root@127.0.0.1> - 2017-05-09 09:27 +0200
              Re: error: initializer element is not constant| Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-09 07:10 -0700
            Re: error: initializer element is not constant| Keith Thompson <kst-u@mib.org> - 2017-05-08 09:30 -0700
  Re: error: initializer element is not constant| John Bode <jfbode1029@gmail.com> - 2017-05-08 08:05 -0700

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