C++ 错误：需要声明
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Error: expected a declaration
提问by Daniel
So far all I have in my DecisionTree.hfile is
到目前为止，我的DecisionTree.h文件中只有
namespace DecisionTree
{
public static double Entropy(int pos, int neg);
}
and Visual Studio is already highlighting the publicand saying
并且 Visual Studio 已经突出显示public和说
Error: expected a declaration.
错误：需要声明。
What am I missing?
我错过了什么？
回答by iammilind
publicis an access specifier. Access specifiers are applicable only within class/structbody and not inside namespace. In C++ (unlike Java) it must be followed by a colon :inside the classbody.
public是访问说明符。访问说明符仅适用于class/structbody 而不适用于inside namespace。在 C++ 中（与 Java 不同），它必须:在class主体内跟一个冒号。
For example,
例如，
class DecisionTree { // <----- 'class' (not 'namespace')
public: // <------ access specifier
static double Entropy (int pos, int neg);
private:
int i;
};
回答by Sai Kalyan Kumar Akshinthala
It will definitely give an error, for you dint declared any class,struct, or enum and directly you have written a static function inside a namespace. So, first write a class definition inside a namespace and then a function.
它肯定会给出错误，因为您 dint 声明了任何类、结构或枚举，并且直接在命名空间内编写了一个静态函数。因此，首先在命名空间中编写类定义，然后编写函数。
