Teach Yourself Borland C++ in 14 Days - portal

154 Day 5
VCL for C++ Programmers
This section is for current C++ programmers moving to C++Builder, but will also be of
interest to new C++ programmers. Although the following is not terribly advanced, it is
aimed at C++ programmers, so if you get lost, muddle your way through and meet us on the
other side.
There are a couple things C++ programmers might find odd when moving to C++Builder.
First, don’t forget that VCL is Object Pascal and not C++. Don’t try to make it C++. The
system works very well as long as you understand that and work within those parameters. All
the code you write will be C++, but remember that VCL itself is not C++. With that in mind,
let me give you a couple things to consider when using VCL.
NOTE
All VCL Objects Must Be Allocated Dynamically
When you drop components on a form, C++Builder automatically writes code that
dynamically creates the components, so you don’t have to think about it. However, you may
need to create and use VCL classes at runtime. For instance, let’s say you needed to display
a File Open dialog box and you didn’t have a TFileOpen component on your form. No
problem—you can just create the object on-the-fly. The code would look something like this:
TOpenDialog* dlg = new TOpenDialog(this);
dlg->Title = “Open a New File”;
dlg->Execute();
Note that the object must be created using the new operator. If you attempt to use local
allocation, you will get a compiler error that says VCL classes must be constructed using
operator new.
Most VCL components can be created at runtime as well as at design
time. It’s easier to create the components at design time because it is
much easier to set the properties using the Object Inspector than it is to
set the properties through code. Still, there are times when you need to
create components at runtime, and C++Builder allows you to do that.
Object Pascal Does Not Support Overloaded Functions;
Hence, VCL Classes Have No Overloaded Constructors
In fact, VCL constructors typically do very little. Take the VCL version of the TRect class,
for instance. In order to construct and set up a TRect object in VCL, you would use code like
this: