C ++类中的静态常量:未定义的引用 [英] static const in c++ class: undefined reference
问题描述
我有一个仅在本地使用的类(即,它的作用仅仅是它在其中定义的c ++文件)
I have a class for local use only (i.e., its cope is only the c++ file it is defined in)
class A {
public:
static const int MY_CONST = 5;
};
void fun( int b ) {
int j = A::MY_CONST; // no problem
int k = std::min<int>( A::MY_CONST, b ); // link error:
// undefined reference to `A::MY_CONST`
}
所有代码都驻留在相同的c ++ 文件中.在Windows上使用VS进行编译时,完全没有问题.
但是,在Linux上编译时,我仅对第二条语句显示undefined reference
错误.
All the code reside in the same c++ file. When compiling using VS on windows, there is no problem at all.
However, when compiling on Linux I get the undefined reference
error only for the second statement.
有什么建议吗?
推荐答案
std::min<int>
的参数都是const int&
(不仅仅是int
),即对int
的引用.而且您不能传递对A::MY_CONST
的引用,因为它没有定义 (仅声明了 ).
std::min<int>
's arguments are both const int&
(not just int
), i.e. references to int
. And you can't pass a reference to A::MY_CONST
because it is not defined (only declared).
在类之外的.cpp
文件中提供定义:
Provide a definition in the .cpp
file, outside the class:
class A {
public:
static const int MY_CONST = 5; // declaration
};
const int A::MY_CONST; // definition (no value needed)
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