C++核心准则SF.4:在其他声明之前include .h文件

SF.4: Include .h files before other declarations in a file

SF.4:在其他声明之前include .h文件

Reason（原因）

Minimize context dependencies and increase readability.

最小化上下文依赖性并提高可读性。

Example（示例）

#include <vector>
#include <algorithm>
#include <string>

// ... my code here ...

Example, bad（反面示例）

#include <vector>

// ... my code here ...

#include <algorithm>
#include <string>

Note（注意）

This applies to both .h and .cpp files.

本规则.h文件和.cpp文件都适用。

Note（注意）

There is an argument for insulating code from declarations and macros in header files by #including headers after the code we want to protect (as in the example labeled "bad"). However

关于在头文件中隔离代码和声明/宏的方式存在其他观点，这种观点建议在需要保护的代码之后include头文件（就像我们注明反面示例的代码）。然而：

• that only works for one file (at one level): Use that technique in a header included with other headers and the vulnerability reappears. 这种方法只适用于一个文件（一层）：一旦在一个被其他头文件引用的头文件中使用这个技术，脆弱性会再次出现。
• a namespace (an "implementation namespace") can protect against many context dependencies. 命名空间（“实现命名空间”）可以防止很多上下文依赖性。
• full protection and flexibility require modules. 完全防止并保持灵活性需要模块功能。

See also（参见）:

• Working Draft, Extensions to C++ for Modules： http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4592.pdf
• Modules, Componentization, and Transition： http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0141r0.pdf

Enforcement（实施建议）

Easy.

容易。

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#sf4-include-h-files-before-other-declarations-in-a-file