如何设计二进制兼容可扩展性的C ++ API [英] How to design a C++ API for binary compatible extensibility

问题描述

我正在设计一个用于C ++库的API，它将分布在dll / shared对象中。库包含具有虚函数的多态类。我担心，如果我公开这些虚拟函数的DLL API，我削减了扩展相同的类与更多的虚拟函数的可能性，而不破坏与为以前的版本的库的应用程序的二进制兼容性。

I am designing an API for a C++ library which will be distributed in a dll / shared object. The library contains polymorhic classes with virtual functions. I am concerned that if I expose these virtual functions on the DLL API, I cut myself from the possibility of extending the same classes with more virtual functions without breaking binary compatibility with applications built for the previous version of the library.

一个选择是使用 PImpl 成语隐藏所有具有虚拟函数，但这似乎也有它的局限性：这种方式应用程序失去子类的类和覆盖虚拟方法的可能性。

One option would be to use the PImpl idiom to hide all the classes having virtual functions, but that also seem to have it's limitations: this way applications lose the possibility of subclassing the classes of the library and overriding the virtual methods.

如何设计一个API类，可以在应用程序中进行子类化，而不会失去在新版本的dll中使用（非抽象）虚拟方法扩展API的可能性，同时保持向后兼容的二进制？

How would you design a API class which can be subclassed in an application, without losing the possibility to extend the API with (not abstract) virtual methods in a new version of the dll while staying backward binary compatible?

更新：库的目标平台是windows / msvc和linux / gcc。

Update: the target platforms for the library are windows/msvc and linux/gcc.

推荐答案

一篇名为在GNU / Linux系统上用C ++实现的共享库的二进制兼容性的文章[ pdf ]。虽然在Windows系统上的概念是相似的，我敢肯定，他们是不一样的。但是阅读这篇文章后，你可以得到一个关于C ++二进制级别与兼容性有什么关系的观点。

Several months ago I wrote an article called "Binary Compatibility of Shared Libraries Implemented in C++ on GNU/Linux Systems" [pdf]. While concepts are similar on Windows system, I'm sure they're not exactly the same. But having read the article you can get a notion on what's going on at C++ binary level that has anything to do with compatibility.

顺便说一下，GCC应用二进制接口在标准文档草案 Itanium ABI 中进行了总结，因此您将有一个正式的理由您选择的编码标准。

By the way, GCC application binary interface is summarized in a standard document draft "Itanium ABI", so you'll have a formal ground for a coding standard you choose.

只是一个快速示例：在GCC中，如果没有其他类继承它，您可以扩展一个具有更多虚函数的类。阅读文章更好的规则集。

Just for a quick example: in GCC you can extend a class with more virtual functions, if no other class inherits it. Read the article for better set of rules.

但无论如何，规则有时太复杂，难以理解。因此，您可能对验证两个给定版本的兼容性的工具感兴趣： abi-compliance-checker for Linux 。

But anyway, rules are sometimes way too complex to understand. So you might be interested in a tool that verifies compatibility of two given versions: abi-compliance-checker for Linux.

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