在头文件中静态成员函数中声明的静态数据有多少个实例？ [英] How many instances are there of static data declared inside a static member function in a header file?

问题描述

我正在使用 xlC 在AIX上编译 Cppcheck $ c>。每个检查器类派生自检查类，其构造函数负责在全局静态列表中注册该类型的检查器。

下面是相关代码的相关部分（文件名链接到Github上的完整源代码）：

check.h

  class Check {
 public：
 Check（）{
 instances（）。push_back（this）; 
 instances（）。sort（）; 
} 
 static std :: list< Check *> & instances（）{
 static std :: list< Check *> _实例; 
 return _instances; 
} 
 // ... 
}; 
  

checkbufferoverrun.h

  class CheckBufferOverrun：public Check {
 // ... 
}; 
  

checkbufferoverrun.cpp

  //注册此检查类通过创建它的静态实例）
命名空间
 {
 CheckBufferOverrun instance; 
} 
  

注意 _instances static变量声明在头文件中的 static 函数中（没有相应的 check.cpp 文件）。当使用 g ++ 编译时，编译器和链接器一起工作，以确保只有一个实现的静态 instances（）函数，因此只有一个静态 _instances 列表的实例。在不同的 .cpp 文件中实例化的所有不同的检查器类在同一个 _instances 列表中注册。

但是，在AIX的 xlC 下，这个代码最终创建了一个不同 instances（）函数为每个 .cpp 文件中包含它，每个都有不同的静态 _instances 列表。因此，不再有一个中心 _instances 列表，这导致Cppcheck不运行大多数检查。

在这种情况下哪个编译器的行为是正确的？

更新：这个问题不是如何解决问题，我已经这么做了。

解决方案

g ++具有正确的行为：应该只是对象的一个​​实例。 C ++标准说（C ++ 03 7.1.2 / 4）：

外部内联函数中的静态局部变量总是指因为类有外部链接，静态成员函数也有外部链接，每个C ++ 03 3.5 / 5：

成员函数...如果类名具有外部链接，则具有外部链接。

因为成员函数在类定义中定义，所以它是一个内联函数，根据C ++ 03 7.1.2 / 3：

在类定义中定义的函数是内联函数。

I'm working on compiling Cppcheck on AIX using xlC. Every checker class is derived from a Check class, whose constructor is responsible for registering that type of checker in a global static list.

Here's the relevant part of the code in question (filenames link to full source on Github):

check.h

class Check {
public:
    Check() {
        instances().push_back(this);
        instances().sort();
    }
    static std::list<Check *> &instances() {
        static std::list<Check *> _instances;
        return _instances;
    }
    // ...
};

checkbufferoverrun.h

class CheckBufferOverrun: public Check {
    // ...
};

checkbufferoverrun.cpp

// Register this check class (by creating a static instance of it)
namespace
{
CheckBufferOverrun instance;
}

Notice how the _instances static variable is declared inside a static function in the header file (there is no corresponding check.cpp file). When compiled with g++, the compiler and linker work together to ensure that there is only one implementation of the static instances() function, and therefore only one instance of the static _instances list. All the different checker classes instantiated in different .cpp files get registered in the same _instances list together.

However, under AIX's xlC, this same code ends up creating a different instances() function for every .cpp file in which it is included, which each having a different static _instances list. So there is no longer a single central _instances list, which causes Cppcheck to not run most of its checks.

Which compiler's behaviour is correct in this case?

Update: This question is not about how to fix the problem, I've already done that. I'm curious about which behaviour is correct.

解决方案

g++ has the correct behavior: there should be exactly one instance of the object. The C++ Standard says (C++03 7.1.2/4):

A static local variable in an extern inline function always refers to the same object.

Because the class has external linkage, the static member function also has external linkage, per C++03 3.5/5:

a member function...has external linkage if the name of the class has external linkage.

Because the member function is defined in the class definition, it is an inline function, per C++03 7.1.2/3:

A function defined within a class definition is an inline function.

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