Re: Can't understand this! (Help required please)

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Date: Sat, 05 Feb 2005 20:04:07 +0000

> I would have expected that if #include <string> was missing,
> the compiler would have complained about using 'std::string'.
> Whatever.

I am using VC++.NET 2003, I thought this was supposed to be one of the
most standards C++ compilers around.

>
> So do I understand that your program compiles now?
> That's just half (often less) of the battle. Now,
> does it work the way you want? Make sure you test
> exhaustively, checking 'boundary conditions', bad
> input, etc.

Well yes it does seem to do the job, since the array initialised is a
string array that feeds the strings to the stack, I am using a fixed
size array, since I dont think it is possible to calcualte the number of
elements using sizeof, but yess it feeds the stack using push, and then
spits them out in reverse order using pop, and noe errors with that
delete and still no errore without it, and task manager seems to
indicate that memory is eventually restored

> <string> is where the << operator for std::string is declared
> (not all the << operators are declared by <ostream>).

Thanks for the tip, I did not realise this

>>One interesting thing you point out is that I do not need delete on the
>>p_arrayString object, this contradicts what our tutor says,
>
>
> Your tutor is wrong (or perhaps you misunderstood her).

Our tutor is never wrong :) except when she is

Another part of the code that I am unsure of is this line
for( int i = 0; i < 3; ++i )
                stringStack.push( new std::string ( arrayString[ i ] ) );

This does indeed use new operator, but my understanding is that the
delete in pop takes care of this?

>
>

> Your understanding is correct. Also note that there are
> special array versions of 'new' and 'delete', and that they
> must not be mixed with the single-object versions. IMO it's
> important that you sort this issue out with your tutor (and if
> she's wrong on this point, I wonder about what else -- this is
> a very fundamental issue). Something to think about.

Yes indeed the delete [] is used with arrays of pointers and delete is
used on single objects, if my understanding is correct.

> A good textbook. See www.accu.org for peer reviews.
> I presume that you have at least one textbook already.
> Which one?

Well I have a few
1. Thinking in CPP 2nd Edition Vol1 - our main course work
2. The mother of all reference books The C++ Language Special Edition -
used as a reference or if I am feeling particularly brave a reading book
3. C++ in action, good but can get confusing at time
4 OO programing with C++ by David Parsons - I like this book alot it
explains things very well and seems to be good at relating C++ material
to real life examples, something a mere mortal like myself appreciates
5. Art of assembly language, perhaps an odd choice of book for someone
learning C++, but it helped me understand the basic fundamentals of data
types and how my computer may represent these in binary hex format etc.

Be warned that there are many bad ones
> out there, which can do more harm than good.

Yes and some online courses NETG does not seem to understand what
ANSI/ISO standards are, with typical code examples like this

void main()
or worse just main()

or how about using int to represent bool types

This was disapointing, and their arrogance to recognise or accept that
the code or teaching is not ANSI/ISO was even more frustrating.

This is one online/CD course to avoid at all costs complete waste of
time and money!!

> many older ones that once were considered 'good'
> are now obsolete. There's only one free online C++
> book I'm willing to recommend: Bruce Eckel's "Thinking
> in C++". www.mindview.net

This is the one I am using now, 2nd Edition Vol1 both book and online, I
like the fact I can open this in VS.Net 2003 and browse this whiule
coding :)

>
> Even if your course has its own 'standard' textbook(s), it's
> often useful to supplement them with others. For the C++
> novice I recommend:

I agree :) right now I eat sleep and breathe C++
>
> New to programming:
> Francis Glassborow's "You Can Do It!"
> http://www.spellen.org/youcandoit/
> (a plus here is that Francis participates
> in this group and at comp.lang.c++)

I have heard of this book, but have limited experiece with VB and
Delphi, I mostly understand the three main building blocks of
programming afaicr
Sequence
Selection
Repetition/iteration

It is supposedly possible to write programs using these three bulding
blocks and nothing else, thus eliminating the infamous goto and gosubs

So not too sure this book will help me a great deal with C++

>
> Experience with programming but new to C++:
> Koenig & Moo's "Accelerated C++"
> www.acceleratedcpp.com

I have heard many many good things about this book, but have never got
around to reading it or buying it perhaps I should make it my next purcahse

>
> You probably won't need it for a while yet, but when the
> time comes, consensus (with which I agree) is that the
> best reference for the C++ standard library is this:
> www.josuttis.com/libbook
> I have found it invaluable.

Even better than The C++ Programming Language ?

>
> And don't forget the FAQs (which contain much Good Stuff):
> alt.comp.lang.learn.c-c++ FAQ:
> http://www.comeaucomputing.com/learn/faq/
> C++ FAQ: http://www.parashift.com/c++-faq-lite/
>

I have heard of comeau don't they make compilers too?

>
>>she explained why,
>
>
> I'd certainly like to hear her explanation. :-)
>

I am not sure why, perhaps it is because Bruce Eckel says :)
look at this listing from the online tutorial

//: C06:Stack3Test.cpp
//{L} Stack3
//{T} Stack3Test.cpp
// Constructors/destructors
#include "Stack3.h"
#include "../require.h"
#include <fstream>
#include <iostream>
#include <string>
using namespace std;

int main(int argc, char* argv[]) {
   requireArgs(argc, 1); // File name is argument
   ifstream in(argv[1]);
   assure(in, argv[1]);
   Stack textlines;
   string line;
   // Read file and store lines in the stack:
   while(getline(in, line))
     textlines.push(new string(line));
   // Pop the lines from the stack and print them:
   string* s;
   while((s = (string*)textlines.pop()) != 0) {
     cout << *s << endl;
     delete s;
   }
} ///:~

My hardcopy book confirms this code too using delete s; in the while
loop I wonder if it should be s = 0;?

This is most odd s is declared once but deleted lots of times, but my
compiler does not complain with this code.

Any ideas?

> I'll be the first to admit C++ is neither a small nor
> simple language.
Can I be the second to admit this :)

Just pay attention to detail and persevere
> (i.e. practice, practice), and you should be fine.

I try to, I am trying to design a small program myself to test my C++
knowledge.

I remeber a game I used to play on my calculator bomber run or
something, a top game that had me addicted, it was simple in conceptbut
highly addictive, I replicated this in VB but perhaps I might do the
same in C++

the graphics were crude the bomber was repesented as > this I would
imagine would be a char* const
the bomb was represented as an v another char* const

and the buldings were like solid blocks unsure what to use there perhaps
  a **** char* const or even a string const

maybe I am just getting carried away :)
And of
> course whenever you get stuck, you can ask here. I try to
> help with what I can, and there are also many more folks
> here who have more skill and experience than I. Be sure to
> read all the replies you might get, this helps you determine
> when someone gives you wrong information or makes a mistake,
> including myself.

I do, and other peoples posts, it's all knowledge for me

>
> More below.
>

> OK now I see why the data is represented as 'void*'. You're
> using the 'C way' of handling generic element types. The
> 'C++ way' would be to use a template. IMO the major problem
> with using 'void*' is that the required cast discards any type
> checking protection the compiler could have provided.

An argument I have used many times myself, I want to learn standard C++,
but I am assured this style of learning will be beneficial in my future
job resume.

I guess there could be some truth in it, I bet not everyone uses
standard C++ and one day I may have the horrific assignment of
deciphering this type of code

>>using namespace std; //

the line above shouldn't be in header files should it?

> You seem to have alluded to it already, but I'll confirm
> it: that code is awful. :-)
>
> Good luck with your studies.
>
> -Mike

Thanks for all your comments and help, they have been really helpful
Rich

• Previous message: Jeff: "help needed Error when entering wrong data type in do-while loop"
• In reply to: Mike Wahler: "Re: Can't understand this! (Help required please)"
• Next in thread: George Huber: "Re: Can't understand this! (Help required please)"
• Reply: George Huber: "Re: Can't understand this! (Help required please)"
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