Quick start manual

Programs and units 3-5
Unit references and the uses clause
So, for example, if you have defined data structures that need to be initialized, you
can do this in the initialization section.
For units in the interface uses list, the initialization sections of units used by a client
are executed in the order in which the units appear in the client’s uses clause.
The finalization section
The finalization section is optional and can appear only in units that have an
initialization section. The finalization section begins with the reserved word
finalization and continues until the end of the unit. It contains statements that are
executed when the main program terminates (unless the Halt procedure is used to
terminate the program). Use the finalization section to free resources that are
allocated in the initialization section.
Finalization sections are executed in the opposite order from initializations. For
example, if your application initializes units A, B, and C, in that order, it will finalize
them in the order C, B, and A.
Once a unit’s initialization code starts to execute, the corresponding finalization
section is guaranteed to execute when the application shuts down. The finalization
section must therefore be able to handle incompletely initialized data, since, if a
runtime error occurs, the initialization code might not execute completely.
Unit references and the uses clause
A uses clause lists units used by the program, library, or unit in which the clause
appears. (For information about libraries, see Chapter 9, “Libraries and packages”).
A uses clause can occur in
• the project file for a program or library,
• the interface section of a unit, and
• the implementation section of a unit.
Most project files contain a uses clause, as do the interface sections of most units. The
implementation section of a unit can contain its own uses clause as well.
The System unit and the SysInit unit are used automatically by every application and
cannot be listed explicitly in the uses clause. (System implements routines for file I/O,
string handling, floating point operations, dynamic memory allocation, and so forth.)
Other standard library units, such as SysUtils, must be included in the uses clause. In
most cases, all necessary units are placed in the uses clause when your project
generates and maintains a source file.
In unit declarations and uses clauses (on Linux particularly), unit names must match
the file names in case. In other contexts (such as qualified identifiers), unit names are
case insensitive. To avoid problems with unit references, refer to the unit source file
explicitly:
uses MyUnit in "myunit.pas";