声明“extern”C“的效果是什么？在头文件到C ++共享库？ [英] What is the Effect of Declaring 'extern "C"' in the Header to a C++ Shared Library?

问题描述

根据这个问题，我了解结构的目的在链接C库与C ++代码。现在假设如下：

Based on this question I understand the purpose of the construct in linking C libraries with C++ code. Now suppose the following:

我有一个'.so'共享库用C ++编译器编译。头部有一个'typedef stuct'和一些函数声明。如果标头包含externC声明...

I have a '.so' shared library compiled with a C++ compiler. The header has a 'typedef stuct' and a number of function declarations. If the header includes the extern "C" declaration...

#ifdef __cplusplus
extern "C"
{
#endif

  // typedef struct ...;
  // function decls

#ifdef __cplusplus
}
#endif

...效果是什么？具体来说，我想知道是否有任何有害的声明的副作用，因为共享库被编译为C ++，而不是C。

... what is the effect? Specifically I'm wondering if there are any detrimental side effects of that declaration since the shared library is compiled as C++, not C.

有任何理由有extern C声明在这种情况下？

Is there any reason to have the extern "C" declaration in this case?

推荐答案

这是重要的，以便编译器不会命名mangle。

This is important so that the compiler doesn't name mangle. C++ uses name mangling to differentiate functions with operator overloads.

对二进制文件运行/ usr / bin / nm，看看C ++对你的函数名是什么：
_ZSt8_DestroyIN9__gnu_cxx17__normal_iteratorIPiSt6vectorIiSaIiEEEEiEvT_S7_SaIT0_E

Run "/usr/bin/nm" against a binary to see what C++ does with your function names: _ZSt8_DestroyIN9__gnu_cxx17__normal_iteratorIPiSt6vectorIiSaIiEEEEiEvT_S7_SaIT0_E

externC可防止该名称的变形。

extern "C" prevents that name mangling.

IIRC，以在运行时动态链接符号。这是插件类型架构的常见问题。

IIRC, that makes it possible for program to dynamically link in symbols at run time. It's common for "plugin" type architectures.

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