NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/2611

Text File | 1996-08-06 | 2.1 KB | 83 lines

Path: atglab.bls.com!Alun.Champion
From: [e-mail] (Alun Champion)
Newsgroups: comp.lang.c++
Subject: Re: using const for structs?
Date: 18 Jan 1996 19:01:11 GMT
Organization: Computer People Inc.
Message-ID: <[e-mail]>
References: <4dm36c$[e-mail]>
NNTP-Posting-Host: bstfirewall.bst.bls.com
In-reply-to: Gerhard Muth's message of 18 Jan 1996 18:23:08 GMT

In article <4dm36c$[e-mail]> Gerhard Muth <muth> writes:

:// If i try to compile it on a HP 700 with
:// $ CC const_struct.C
:// i get the following error message:
:// CC: "const_struct.C", line 35: error: cannot make a box (1284)
://
:// I think, that i have to write a 2-parameter constructor,
:// but the book does not tell anything about that. It just says:
://
://     "The #define directive is limited to defining simple
://      constants. The const statement can define almost any
://      type of C++ constant including things such as
://      structure classes."
://
:// Question: Is the book wrong or is the compiler just bad?

: struct box {
       float width, heigth; // float was int before
: };

: const box blue_box();

I don't think this line does what you expected - this declares
a function that returns a const box and takes no parameters.
I believe you meant:

  const box blue_box;

: const box pink_box(1.0, 4.5); // this is line 35

This is a constructor call which you have not provided for struct
box. The book is not wrong and compiler is not bad. You can declare
initialise this struct like:

  const box pink_box = { 1.0, 4.5 };

or you can define a constructor for struct box:

  struct box {
      box(float w = 0.0, float h = 0.0) : width(w), height(h)
      { }

      float width, heigth; // float was int before
  };

now this works:

  const box pink_box(1.0, 4.5);

and so does:

  const box blue_box;

and:

  const box green_box(4.0);

: void main(void) {}

This has undefined behaviour - main should be declared

  int main(void)
or
  int main(int argc, char* argv[])

Hope this helps
Regards
   -A.
--
| A.Champion                |