c++ - 对于内联函数和 constexpr 函数， "obey ODR"是什么意思？

Question

我刚读到 constexpr 和 inline 函数遵循一个定义规则，但它们的定义必须相同。所以我试了一下:

inline void foo() {
    return;
}

inline void foo() {
    return;
}

int main() {
    foo();
};

错误:'void foo()' 的重新定义，
和

constexpr int foo() {
    return 1;
}

constexpr int foo() {
    return 1;
}

int main() {
    constexpr x = foo();
}; 

错误:'constexpr int foo()' 的重新定义

那么究竟是什么意思，constexpr 和 inline 函数可以服从 ODR？

Answer 1

I just read that constexpr and inline functions obey one-definition rule, but they definition must be identical.

这是引用不同翻译单元中的内联函数。在您的示例中，它们都在同一个翻译单元中。

这包含在 draft C++ standard 中3.2 一个定义规则 [basic.def.odr] 说:

There can be more than one definition of a class type (Clause 9), enumeration type (7.2), inline function with external linkage (7.1.2), class template (Clause 14), non-static function template (14.5.6), static data member of a class template (14.5.1.3), member function of a class template (14.5.1.1), or template specialization for which some template parameters are not specified (14.7, 14.5.5) in a program provided that each definition appears in a different translation unit, and provided the definitions satisfy the following requirements. Given such an entity named D defined in more than one translation unit, then

并包括以下项目符号:

• each definition of D shall consist of the same sequence of tokens; and