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Internet Message Format | 1996-08-05 | 3.0 KB

Path: newsfeed.internetmci.com!panix!not-for-mail
From: [e-mail] (Arthur Cinader Jr)
Newsgroups: comp.lang.c++,gnu.g++.help
Subject: Re: DONT UNDERSTAND - array of char error
Date: 3 Mar 1996 09:50:22 -0500
Organization: Panix
Message-ID: <4hcbje$[e-mail]>
References: <4habvu$[e-mail]> <4hahju$[e-mail]>
NNTP-Posting-Host: panix.com

In <4hahju$[e-mail]> [e-mail] (Dietmar Kuehl) writes:

Dietmar,

Wow, thanks.  I love the internet and thank you for your kind
assistance!

>Well, because you forgot about an important restriction on arrays: All
>but the first dimension has to be fixed at compile-time.

>: In the definition (.C) file, I use the comand:

>:     labels = new char[maxargs][fieldlength]; // make label array
>:     params = new char[maxargs][fieldlength]; // make params array

>... i.e. 'fieldlength' has to be a 'const'. If 'fieldlength' is
>non-const you have to allocate the second dimension by hand (unless you
>use an array class like suggested below):

I thought I covered this by making

    const int fieldlength;

and using a member intializer like this:

    Param::Param(char *shape)
        :maxargs(10), fieldlength(20)

In any event, what you showed me below is what I wanted to
do, but couldn't come up with on my own...

>  lables = new char *[maxargs]; // it is valid to allocate an array
>  params = new char *[maxargs]; // of 'char*'
>  for (int i = 0; i < maxargs; i++)
>  {
>    labels[i] = new char[fieldlength]; // ... and to allocate an
>    params[i] = new char[fieldlength]; // of 'char'.
>  }

>... but an array thus create has to be destructed like this:

>  for (int i = maxargs; i--; )
>  {
>    delete[] params[i];
>    delete[] lables[i];
>  }
>  delete params;
>  delete lables;

>Which is, IMHO, far to dangerous to be done: Given that you run out of
>memory, you are likely to end up with a serious memory-leak. I know how
>to program in C++ and I won't do it like this... This is exactly the
>problem I have with all C++ tutorials I have seen until know: They
>introduce the low-level methods, requiring to be an expert to handle
>them correctly, but they don't introduce the clean methods provided by
>the (upcoming) ISO Standard C++ Library (to be fair: this library was
>introduced into the standard quite recently, i.e. sometime in 1994). A
>clean method is to use the 'vector' class found in libg++ starting with
>libg++-2.6.? (you didn't mention what version you are using but I
>assume a recent one, e.g. 2.7.2):


Your point noted, but I am going to risk it in this case.  I
am overwhelmed enough without having to stop now to figure out
how to use the libraries and understand their interface.  I do
recognize this as a crucial part of my becoming productive and
I will endevour to find documentation on the ISO standard
library and learn about how to use it.  FWIW the next chapter
in the text is on I/O streams which I believe spends a
considerable amount of time explaining "pre-packaged" class
hiararchies and how to navigate them.


Thanks again Dietmar.

Best Regards,

Arthur