C语言简明面向对象编程指南
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更新于2024-07-19
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本资源是一份名为"AN_Simple_OOP_in_C"的C语言应用笔记，由QuantumLeaps, LLC发布，主要针对C语言使用者介绍了简单面向对象编程的概念和实践。文档详细地探讨了封装、继承、多态性（特别是虚函数）等核心概念。
1. **介绍**：文档首先引导读者了解面向对象编程（Object-Oriented Programming, OOP）在C语言中的应用，强调它如何简化代码管理和复用性，对于熟悉C语言但希望提升其面向对象编程能力的开发者非常实用。
2. **封装**：章节2讲解了封装的重要性，即数据隐藏和访问控制，使得对象内部实现细节对外部不可见，仅通过预定义的接口进行交互。这有助于保护数据安全并保持设计的灵活性。
3. **继承**：第四部分深入剖析了C语言中的继承机制，包括子类如何继承父类的属性和方法，以及如何通过基类指针调用基类的方法，为代码重用提供了基础。
4. **多态与虚函数**：
- **虚拟表（Virtual Table, vtbl）和虚拟指针（Virtual Pointer, vptr）**：这部分详细解释了如何利用虚函数表来存储所有可能的函数实现，以及如何通过虚指针动态调用正确的函数版本。
- **构造函数中的vptr设置**：讲解了如何在子类构造函数中初始化vptr，确保正确指向子类的实例。
- **子类继承vtbl和重写vptr**：阐述了子类如何继承父类的vtbl，并在必要时重写虚函数，实现多态行为。
- **虚拟调用（Late Binding）**：解释了为何在运行时而不是编译时确定函数调用是多态的关键，提高了代码的灵活性。
5. **使用虚函数的例子**：通过具体的代码示例，展示了如何在实际项目中运用这些概念，帮助读者更好地理解和掌握面向对象编程在C语言中的应用。
6. **总结**：最后部分是对整个文档内容的概括，重申了面向对象编程在C语言中的优势，以及如何通过合理使用这些概念提高程序的可维护性和扩展性。
7. **参考文献**：列出了一些相关的参考资料，供读者进一步探索相关主题。
8. **联系信息**：文档提供了QuantumLeaps公司的联系方式，以便读者寻求技术支持或咨询。
9. **法律免责声明**：文档明确声明，尽管信息被尽力保证准确，但QuantumLeaps不对信息的准确性或完整性做出任何保证，并且不承担因使用信息而产生的后果。
这份简明扼要的文档为C语言开发人员提供了一套实用的面向对象编程指南，无论是初学者还是经验丰富的开发者都能从中受益。
Copyright © Quantum Leaps, LLC. All Rights Reserved.
1 Introduction
Object-oriented programming (OOP) is not the use of a particular language or a tool. It is rather a way of
design based on the three fundamental design meta-patterns:
• Encapsulation – the ability to package data and functions together into classes
• Inheritance – the ability to define new classes based on existing classes in order to obtain reuse and
code organization
• Polymorphism – the ability to substitute objects of matching interfaces for one another at run-time
Although these meta-patterns have been traditionally associated with object-oriented languages, such as
Smalltalk, C++, or Java, you can implement them in almost any programming language including portable
ANSI-C
[1,2,3,4,5,6]
.
If you develop end-user programs in C, but you also want to do OOP, you probably should be using
C++ instead of C. Compared to C++, OOP in C can be cumbersome and error-prone, and rarely
offers any performance advantage.
However, if you build or use application frameworks, such as the the QP/C and QP-nano active
object frameworks, the OOP concepts are very useful as the primary mechanisms of customizing,
specializing, and extending the frameworks into applications. In that case, most difficulties of doing
OOP in C can be confined to the framework and can be effectively hidden from the application
developers. This Application Note has this primary use case in mind.
This Application Note describes how OOP is implemented in the QP/C and QP-nano active object (actor)
frameworks. As a user of these frameworks, you need to understand the techniques, because you will
need to apply them also to your own application-level code. But these techniques are not limited only to
developing QP/C or QP-nano applications and are applicable generally to any C program.
2 Encapsulation
Encapsulation is the ability to package data with functions into classes. This concept should actually
come as very familiar to any C programmer because it’s quite often used even in the traditional C. For
example, in the Standard C runtime library, the family of functions that includes
fopen()
,
fclose()
,
fread()
, and
fwrite()
operates on objects of type
FILE
. The
FILE
structure is thus encapsulated
because client programmers have no need to access the internal attributes of the
FILE struct
and
instead the whole interface to files consists only of the aforementioned functions. You can think of the
FILE
structure and the associated C-functions that operate on it as the
FILE
class. The following bullet
items summarize how the C runtime library implements the
FILE
class:
1. Attributes of the class are defined with a C
struct
(the
FILE struct
).
2. Operations of the class are defined as C functions. Each function takes a pointer to the attribute
structure (
FILE *
) as an argument. Class operations typically follow a common naming convention
(e.g., all
FILE
class methods start with prefix
f
).
3. Special functions initialize and clean up the attribute structure (
fopen()
and
fclose()
). These
functions play the roles of class constructor and destructor, respectively.
You can very easily apply these design principles to come up with your own “classes”. For example,
suppose you have an application that employs two-dimensional geometric shapes (perhaps to be
rendered on an embedded graphic LCD). The basic
Shape
“class” in C can be declared as follows:
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