[英]C++ error: not a member OR multiple definition
I am trying to use a static const field which I define inside a class. 我试图使用我在类中定义的静态const字段。
When I define it like that: 当我这样定义时:
class DisjunctionQuery : public Query
{
public:
DisjunctionQuery ();
static const std::string prefix;
};
const std::string DisjunctionQuery::prefix = "Or";
It says: multiple definition of 'DisjunctionQuery::prefix' and if I change it that way (remove the two lines): 它说:'DisjunctionQuery :: prefix'的多重定义,如果我改变它(删除两行):
class DisjunctionQuery : public Query
{
public:
DisjunctionQuery ();
//static const std::string prefix;
};
//const std::string DisjunctionQuery::prefix = "Or";
It says when I try to call it in another place 'prefix' is not a member of 'DisjunctionQuery'. 它说当我尝试在另一个地方调用它时,'prefix'不是'DisjunctionQuery'的成员。
How can I make it work? 我怎样才能使它工作? thanks.
谢谢。
You move the definition to a single implementation file. 您将定义移动到单个实现文件。
If you keep it in the header, you'll break the one definition rule . 如果将其保留在标题中,则会破坏一个定义规则 。 Each file that includes the header will attempt to define the
static
member, which is wrong. 包含标头的每个文件都将尝试定义
static
成员,这是错误的。
//DisjunctionQuery.h
class DisjunctionQuery : public Query
{
public:
//....
static const std::string prefix;
};
//DisjunctionQuery.cpp
#include "DisjunctionQuery.h"
const std::string DisjunctionQuery::prefix = "Or";
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