Teach Yourself Borland C++ in 14 Days - portal

122 Day 4
NOTE
Basic File I/O
Classes in VCL do not support multiple inheritance. You can still use
multiple inheritance in any classes you write for use in your C++Builder
applications.
It won’t be long before you are going to need the ability to read and write files in your
applications. I saved this discussion for now because you needed an understanding of classes
in order to understand how file input and output is handled in C++.
If you are going to be doing heavy database operations with C++Builder, you might be
relieved to know that you don’t have to worry about dealing with reading and writing
database files directly. That is all handled for you behind the scenes through C++Builder’s
VCL database components. VCL also provides support for reading and writing the contents
of edit controls, list boxes, and other basic Windows controls. The Windows API provides
functions for reading configuration files (.INI files). Many OCX and ActiveX controls know
how to save and load files specific to the type of action the control performs.
As you can see, many of the objects you will use in C++Builder will handle file I/O for you.
Still, there will be times when you have to read and write your own files, and you’ll need a
basic understanding of file I/O in order to do that.
Basic file I/O is accomplished via three C++ classes:
■ The ofstream class, which handles file output
■ The ifstream class, which handles file input
■ The fstream class, which handles both file input and output
These classes are derived from the iostream class. You have had some experience with
iostream already, although you may not know it. The cout and cin classes I have been using
for console input and output are also derived from iostream. iostream itself is derived from
a class called ios, which is the base class for all stream input and output in C++.
Does this sound complicated? Well, it is. Sometimes the labyrinth of the streaming classes
can be pretty confusing. What I am going to do here is give you a cursory glance at file I/O,
but then we’ll have to move on. You’ll be relieved to know that basic file I/O is not terribly
complicated. If you need to do sophisticated file operations, you’ll need to dig into the class
library help files or get a good book on C++ (such as Teach Yourself Borland C++ 4.5 in 21
Days, Second Edition by Sams Publishing) that deals with file I/O in detail.