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From: CoryG89 on 22 Jun 2010 23:08
Ok, so I am working on this for school. I am building a model
business application in the console using C++.

The application is modeled as a database/cashier program. I have a
class called BookData that is supposed to hold a number of character
arrays and a few other variables.

Here are my private members:


char _isbn[14];
char _title[51];
char _author[31];
char _publisher[31];
char _date[11];
int _quantity;
double _cost;
double _price;


I am supposed to have public accessor and mutator functions that 'get'
and set' each private member of the class. I was surprised to learn
this, but apparently you cannot return an array from a function in C++

Normally I know I would write an accessor function for the last three
similar to something like this:


double BookData::getCost()
{
return _cost;
}


I am not sure how I should go about doing this for the character
arrays. This is for a C++ course and I believe I am supposed to keep
the c strings and not use strings from the standard libraries. I
cannot remember but I think that you are supposed to use pointers to
do this somehow. I tried but the syntax seems clumsy and I am getting
errors. Any tips would be most appreciated.

This is supposed to work by booting up and filling a dynamically
allocated array of BookData class objects from a delimited data file.
I need these 'setter' / 'getter' functions for accessing and
manipulating these values to add other functionality. I am going to be
working on this for the rest of tonight and all tomorrow. So anyone
that can give me any advice on this subject would be most helpful.

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From: Martin B. on 23 Jun 2010 20:03
CoryG89 wrote:
> Ok, so I am working on this for school. I am building a model
> business application in the console using C++.
>
> The application is modeled as a database/cashier program. I have a
> class called BookData that is supposed to hold a number of character
> arrays and a few other variables.
>
> Here are my private members:
>
>
> char _isbn[14];
> char _title[51];
> char _author[31];
> char _publisher[31];
> char _date[11];
> int _quantity;
> double _cost;
> double _price;
>
>

Leading underscores in names are reserved in C/C++
Consider naming your members "m_isbn" or "isbn_" or maybe just "isbn".

> I am supposed to have public accessor and mutator functions that 'get'
> and set' each private member of the class. I was surprised to learn
> this, but apparently you cannot return an array from a function in C++
>

No you cannot. You can only return a pointer. If you have been given
this exercise they should already have tried to explain pointers and
arrays and how they relate to each other in C/C++.

> Normally I know I would write an accessor function for the last three
> similar to something like this:
>
>
> double BookData::getCost()
> {
> return _cost;
> }
>

This function should probably be defined as
double BookData::getCost() const;
But then maybe that's not too important for a beginner.

>
> I am not sure how I should go about doing this for the character
> arrays. This is for a C++ course and I believe I am supposed to keep
> the c strings and not use strings from the standard libraries. I
> cannot remember but I think that you are supposed to use pointers to
> do this somehow. I tried but the syntax seems clumsy and I am getting
> errors. Any tips would be most appreciated.
>

Well for practise it might make sense to forego std::string. For your
array members you can use:

void BookData::setTitle(const char* title) {
assert(title); // Make sure we do not get passed a NULL pointer
strncpy(m_title, title, 14); // attn: constants used - not good
m_title[13] = '\0'; // Make sure always null terminated
}

const char* BookData::getTitle() {
return m_title;
}


Now, that's not too clumsy, or is it?


br,
Martin

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From: Bo Persson on 23 Jun 2010 20:01
CoryG89 wrote:
> Ok, so I am working on this for school. I am building a model
> business application in the console using C++.
>
> The application is modeled as a database/cashier program. I have a
> class called BookData that is supposed to hold a number of character
> arrays and a few other variables.
>
> Here are my private members:
>
>
> char _isbn[14];
> char _title[51];
> char _author[31];
> char _publisher[31];
> char _date[11];
> int _quantity;
> double _cost;
> double _price;
>
>
> I am supposed to have public accessor and mutator functions that
> 'get' and set' each private member of the class. I was surprised to
> learn this, but apparently you cannot return an array from a
> function in C++
>
> Normally I know I would write an accessor function for the last
> three similar to something like this:
>
>
> double BookData::getCost()
> {
> return _cost;
> }
>
>
> I am not sure how I should go about doing this for the character
> arrays. This is for a C++ course and I believe I am supposed to
> keep the c strings and not use strings from the standard libraries.
> I cannot remember but I think that you are supposed to use pointers
> to do this somehow. I tried but the syntax seems clumsy and I am
> getting errors. Any tips would be most appreciated.

The syntax IS clumpsy and error prone - that's why C++ introduced std::string. To otherwise get access to an array, the C way is returning a pointer to the first character.

>
> This is supposed to work by booting up and filling a dynamically
> allocated array of BookData class objects from a delimited data
> file. I need these 'setter' / 'getter' functions for accessing and
> manipulating these values to add other functionality. I am going to
> be working on this for the rest of tonight and all tomorrow. So
> anyone that can give me any advice on this subject would be most
> helpful.

I'm not sure it is a good idea to have separate setters for all values, for example I would think you cannot change publisher without also changing the publishing date. And how often do you change the author's name for a published book?


Bo Persson



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