C++跨平台编程指南：实现无缝移植
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"portablecpp.pdf - C++移植指南，由David Williams撰写，后由Scott Collins和Christopher Blizzard更新维护，提供了使C++代码在不同机器和编译器间具有可移植性的规则、指导和建议。这份资料是基于大量代码在大约25种不同机器和至少12种不同C++编译器上的移植经验总结。"
C++移植性是软件开发中的一个重要主题，特别是在需要跨平台运行或在不同硬件和软件环境中保持兼容性的项目中。以下是一些关键的C++移植性知识点：
1. **遵循标准**：确保你的C++代码完全符合C++标准。不同编译器对非标准扩展的支持程度不同，这可能导致代码在某些平台上无法正确工作。
2. **避免依赖特定编译器特性**：尽量不要使用特定编译器的特殊功能或宏，例如GCC的`__attribute__((packed))`或者MSVC的`__declspec(dllexport)`。如果必须使用，可以使用条件编译指令`#ifdef`进行封装。
3. **模板和泛型编程**：利用模板和泛型编程来实现代码复用，但要注意不同编译器对模板的实现可能有差异，可能导致链接错误。使用模板时，尽量减少依赖于特定实现的细节。
4. **内存管理和智能指针**：使用标准库提供的智能指针（如`std::unique_ptr`和`std::shared_ptr`）代替原始指针，以自动管理内存，避免内存泄漏。这有助于在不同的内存模型下保持一致性。
5. **异常安全**：编写异常安全的代码，确保在抛出异常时，资源能得到适当的释放。理解并使用异常安全的构造函数和析构函数，如资源获取即初始化（RAII）原则。
6. **静态与动态库**：了解不同平台下静态库和动态库的使用方式，以及如何正确链接。例如，Windows上的`.lib`和`.dll`与Linux上的`.a`和`.so`。
7. **文件路径和操作系统接口**：使用`<filesystem>`库（C++17及以上版本）或`boost::filesystem`处理文件路径，避免直接使用操作系统的API，以确保跨平台兼容性。
8. **编译选项和预处理器宏**：统一设置编译选项，并使用预处理器宏来检测平台特征。例如，`#ifdef __linux__`或`#ifdef _WIN32`。
9. **线程和并发**：使用C++11及更高版本的`<thread>`库进行多线程编程，而不是依赖于特定平台的线程API。注意线程安全和同步机制的移植性问题。
10. **编译和链接过程**：了解不同平台的编译和链接过程，例如动态链接与静态链接的区别，以及如何处理依赖项。
遵循以上规则，你的代码将更有可能在Mozilla等多平台环境下无缝运行，并且易于移植到新的硬件或软件环境。定期更新和维护这些知识，以适应不断变化的编译器特性和标准发展。
}
}
Static constructors don't work reliably either. A static initialized object is an object which is instanciated at
startup time (just before main() is called). Usually there are two components to these objects. First there is
the data segment which is static data loaded into the global data segment of the program. The second part is a
initializer function that is called by the loader before main() is called. We've found that many compilers do
not reliably implement the initializer function. So you get the object data, but it is never initialized. One
workaround for this limitation is to write a wrapper function that creates a single instance of an object, and
replace all references to the static initialized object with a call to the wrapper function:
Portable example:
static FooBarClass* static_object;
FooBarClass*
getStaticObject()
{
if (!static_object)
static_object =
new FooBarClass(87, 92);
return static_object;
}
void
bar()
{
if (getStaticObject()->count > 15) {
...
}
}
Don't use exceptions.
Exceptions are another C++ feature which is not very widely implemented, and as such, their use is not
portable C++ code. Don't use them. Unfortunately, there is no good workaround that produces similar
functionality.
One exception to this rule (don't say it) is that it's probably ok, and may be necessary to use exceptions in
some machine specific code. If you do use exceptions in machine specific code you must catch all exceptions
there because you can't throw the exception across XP (cross platform) code.
3.
Don't use Run-time Type Information.
Run-time type information (RTTI) is a relatively new C++ feature, and not supported in many compilers.
Don't use it.
If you need runtime typing, you can achieve a similar result by adding a classOf() virtual member function
to the base class of your hierarchy and overriding that member function in each subclass. If classOf()
returns a unique value for each class in the hierarchy, you'll be able to do type comparisons at runtime.
4.
Don't use namespace facility.
Support of namespaces (through the namespace and using keywords) is a relatively new C++ feature, and
not supported in many compilers. Don't use it.
5.
main() must be in a C++ file.
The first C++ compiler, Cfront, was in fact a very fancy preprocessor for a C compiler. Cfront reads the C++
code, and generates C code that would do the same thing. C++ startup is slightly different to C startup (for
example static constructor functions must be called for C++), and Cfront implements this special startup by
noticing the function called "main()", converting it to something else (like "__cpp__main()"), adding
another main() that does the special C++ startup things and then calls the original function. Of course for all
this to work, Cfront needs to see the main() function, hence main() must be in a C++ file. Most compilers
lifted this restriction years ago, and deal with the C++ special initialization duties as a linker issue. But there
are a few commercial compilers shipping that are still based on Cfront: HP, and SCO, are examples.
6.
C++ portability guide
http://www.cs.umd.edu/users/cml/cstyle/mozilla-portable-cpp.html (3 of 15) [10/1/2000 7:42:12 PM]
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