🚀 go-pugleaf

acinader@panix.com (Arthur Cinader) wrote:

>I am teaching myself to program with "How To Program C++" by
>Deitel & Deitel.  A great book. 

Maybe...  But if their book is so great, why didn't their code work?
=)  I recommend The C++ Primer Plus by Prata, but anyways...  I can
explain the problem in their code.

>Using g++ v2.4 on BSDI I compile with:
>g++ -o fig8.3 fig8.3.C

You can just type g++ fig8.3.cpp


>// overloaded stream extraction operator
>istream &operator>>(istream &input, PhoneNumber &num)
>{
>   input.ignore();                 // skip (
>   input.getline(num.areaCode, 4); // input area code
>   input.ignore(2);                // skip ) and space
>   input.getline(num.exchange, 4); // input exchange
>   input.ignore();                 // skip dash (-)
>   input.getline(num.line, 5);     // input line

The problem lies here.  cin.getline is supposed to be used for reading
all the characters on a line (spaces included) up until the newline
and then ignoring the newline character.  As a sefety measure to
ensure you don't fill your string beyond it's bounds, you can pass an
optional integer to cin.getline to tell it when to stop the input.
With g++, cin.getline skips over the remaining characters on the line
until it reads in and ignores the newline.  However, with Borland C++,
it leaves the remaining characters and newline intact.  In other
words, the author probably was using Borland C++ and failed to test
his program with g++ for UNIX.  The two versions have some
differences..  =)  So basically with your C++ compiler it read the
first four characters and then ignored the rest of the input, hence
the result you were getting...

But all is not lost...  If you use cin.get instead of cin.getline this
code will work perfectly under both compilers.  The author of your
book used the wrong method for the wrong purpose.

Hope this help!

	Nate

Arthur Cinader wrote:
> 
> I am teaching myself to program with "How To Program C++" by
> Deitel & Deitel.  A great book.  In chapter eight, there is a
> an example in the text on operator overloading.  When I code
> the example, exactly as it appears in the book, I don't get
> the output that they show...
> 
> Using g++ v2.4 on BSDI I compile with:
> 
> g++ -o fig8.3 fig8.3.C
> 
> here is the source:
> 
> ********begin source
> // FIG8_3.CPP
> // Overloading the stream-insertion and
> // stream-extraction operators.
> #include <iostream.h>
> 
> class PhoneNumber {
>    friend ostream &operator<<(ostream &, const PhoneNumber &);
>   friend istream &operator>>(istream &, PhoneNumber &);
> private:
>    char areaCode[4];  // 3-digit area code and null
>    char exchange[4];  // 3-digit exchange and null
>    char line[5];      // 4-digit line and null
> };
> 
> // Overloaded stream insertion operator (cannot be
> // a member function).
> ostream &operator<<(ostream &output, const PhoneNumber &num)
> {
>    output << "(" << num.areaCode << ") "
>           << num.exchange << "-" << num.line;
> 
>    return output;     // enables cout << a << b << c;
> }
> 
> // overloaded stream extraction operator
> istream &operator>>(istream &input, PhoneNumber &num)
> {
>    input.ignore();                 // skip (
>    input.getline(num.areaCode, 4); // input area code
>    input.ignore(2);                // skip ) and space
>    input.getline(num.exchange, 4); // input exchange
>    input.ignore();                 // skip dash (-)
>    input.getline(num.line, 5);     // input line
> 
>    return input;      // enables cin >> a >> b >> c;
> }
> 
> main()
> {
>    PhoneNumber phone; // create object phone
> 
>    cout << "Enter a phone number in the "
>         << "form (123) 456-7890:" << endl;
> 
>    // cin >> phone invokes operator>> function by
>    // issuing the call operator>>(cin, phone).
>    cin >> phone;
> 
>    // cout << phone invokes operator<< function by
>    // issuing the call operator<<(cout, phone).
>    cout << "The phone number entered was:" << endl
>         << phone << endl;
>    return 0;
> }
> 
> *******end source
> 
> Here is the execution:
> 
> % ./fig8.3
> Enter a phone number in the form (123) 456-7890:
> (800) 555-1212
> The phone number entered was:
> (800) -
> %
> 
> The output should be the full number.
> 
> I tested the value of the PhoneNumber object with
> printExchange() and printLine() functions.  Both print
> funtions printed nothing leading me to conclude that the
> culprit is the function:
> 
> friend istream &operator>>(istream &, PhoneNumber &);
> 
> I am stumped!  Is there a switch I need to throw to make
> operator overloading work with g++?  A search of the man pages
> has turned up nothing.
> 
> Thnaks for any light you can shed!
> 
> Best Regards,
> 
> Arthur
> acinader@panix.com

Try out this for your input function:

// overloaded stream extraction operator
istream &operator>>(istream &input, PhoneNumber &num)
{
   input.ignore();                 // skip (
   input.get(num.areaCode, 4, ')'); // input area code
   input.ignore(2);               // skip ) and space
   input.get(num.exchange, 4, '-'); // input exchange
   input.ignore();                 // skip dash (-)
   input.getline(num.line, 5);     // input line

   return input;      // enables cin >> a >> b >> c;
}

The function getstring seems to read the whole line, so it was 'eaten'
when you read your areaCode.

Oliver Kurth