Original

Programs and units

A program is constructed from source-code modules called units. Each unit is stored in its own file and compiled separately; compiled units are linked to create an application. Units allow you to

·divide large programs into modules that can be edited separately.

·create libraries that you can share among programs.

·distribute libraries to other developers without making the source code available.

In traditional Pascal programming, all source code, including the main program, is stored in .pas files. Borland tools use a project (.dpr) file to store the main program, while most other source code resides in unit (.pas) files. Each application or project consists of a single project file and one or more unit files. (Strictly speaking, you needn’t explicitly use any units in a project, but all programs automatically use the System unit.) To build a project, the compiler needs either a source file or a compiled unit file for each unit.

Topic groups

Programs and units: Overview

Program structure and syntax: Overview

The program heading

The program uses clause

The block

Unit structure and syntax: Overview

The unit heading

The interface section

The implementation section

The initialization section

The finalization section

Unit references and the uses clause

The syntax of a uses clause

Multiple and indirect unit references

Circular unit references

程序和单元

由源代码模块的程序叫做单元。每个单元保存在各自相应的文件中并且分别编译；编译过的单元被连接用于创建应用程序。单元允许开发者

· 将大的程序组分成可以分别编辑的若干模块。

· 在程序组中创建共享库。

· 向其他的开发者分发库（编译过的单元）而保留源代码。

在传统的Pascal编程中，所有的源代码，包括主程序，都保存在.pas文件中。Borland开发工具用工程（.dpr）文件存储主程序，而将大多数其他的源代码驻留在单元（.pas）文件中。每个应用程序或工程都是由一个工程文件和一个或更多的单元文件组成。（严格地说，尽管有时在工程中不需要明确通过uses子句使用任何单元，但所有的程序都会自动使用System单元。）要建立一个工程，编译器需要每个单元的源代码（.pas）文件或编译过的单元（.dcu）文件。