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[英]How to initialize a static member variable using a static member function at runtime?
[英]How to initialize static constant member using function
在一个非常简化的情况下,我具有以下设置,在该设置中,我只想从A类的函数中初始化一个常量静态成员(foo类)(单例和实例与该问题无关):
class A
{
public:
static A instance;
A & getInstance() { return instance; }
int i(){ return 10;}
int j(){ return 20;}
};
class foo {
public:
static const int ii = A::getInstance().i() * A::getInstance().j();
};
const int foo::ii;
int main()
{
foo f;
return 1;
}
目的是使用上述某些函数初始化成员ii。 但它会产生以下错误:
$ c++ static_constant.cpp
static_constant.cpp:14:30: error: ‘A::getInstance()’ cannot appear in a constant-expression
static_constant.cpp:14:42: error: a function call cannot appear in a constant-expression
static_constant.cpp:14:44: error: ‘.’ cannot appear in a constant-expression
static_constant.cpp:14:46: error: a function call cannot appear in a constant-expression
static_constant.cpp:14:53: error: ‘A::getInstance()’ cannot appear in a constant-expression
static_constant.cpp:14:65: error: a function call cannot appear in a constant-expression
static_constant.cpp:14:67: error: ‘.’ cannot appear in a constant-expression
static_constant.cpp:14:69: error: a function call cannot appear in a constant-expression
你能帮我吗? 会赞赏的。
您将getInstance
用作静态函数,但未将其声明为static
。
更改getInstance
的声明:
static A & getInstance() { return instance; }
代码有几个问题,但这是一个完整的可编译示例:
class A
{
public:
static A instance;
static A & getInstance() { return instance; }
int i(){ return 10;}
int j(){ return 20;}
};
class foo {
public:
static const int ii;
};
const int foo::ii = A::getInstance().i() * A::getInstance().j();
A A::instance;
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