Re: [Newbie] How to use a class in C++

From:

"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 15 Nov 2011 08:15:52 +0100

Message-ID:

<j9t3jb$iei$1@dont-email.me>

On 15.11.2011 07:19, pozz wrote:

I have a medium experience in C and now I'm learning C++. I have some
difficulties to think by and use classes, so with object oriented
programming.

In my application I have a configuration file that stores some
settings in non-volatile way. Several parts, modules and classes could
access the configuration file both for reading and writing settings.

In C I can create settings.h with the interface:
---
int settings_read(const char *name, char *value, size_t valuesize);
int settings_save(const char *name, const char *value);
---
Every other module that wants to use the settings facilities will
include "settings.h" and user settings_read() and settings_write().
The implementation and any additional data (such as the filename) are
hidden in settings.c.

In C++ I was trying to create a class in settings.h, but I'm not sure
if I should add private data there:
---
class Settings {
const char filename[] = "settings.ini";

Use a std:.string.

Don'e make it `const`.

public:
void Settings(void);
virtual ~Settings(void);

`void` to indicate "no arguments" is a C-ism. It's necessary in C. It's
not necessary in C++.

int settings_read(const string name, string value);

Better pass by reference, like

int read( string const& name, string const& value );

int settings_save(const string name, const string value);
};
---
Why the user should know about private data, like filename? I'm
tempted to avoid adding private data/functions in the class
declaration in settings.h, but in settings.c as typical static names
(like in C). I don't know if this is a good approach, because I have
seen many C++ source files with private names in include file.

The difference with a class is that the using code creates an instance
of it.

Each instance can have its own filename.

Cheers & hth.,

- Alf