在C++中转发“预先声明”一个类-Forward“Pre-declaring”aClassinC++

You could define it inside the class:

你可以在类中定义它:

class Substring {
    private:
        string the_substring_;
    public:
        // (...)
        typedef set SubstringTree;
        static SubstringTree getAllSubstring(string main_string, int min_size);
};

As you've written it, the short answer is you can't.

正如你所写,简短的回答是你不能。

You do have a few close alternatives:

你有几个接近的选择:

1) Declare SubstringTree in Substring

1)在子串中声明SubstringTree

class Substring {
public:
    class Comparator;
    typedef set Tree;

private:
    string the_substring_;
public:
    // (...)
    static Tree getAllSubstring(string main_string, int min_size);
};

typedef Substring::Tree SubstringTree;

2) Define the Comparator outside of Substring:

2)在子串外定义比较器:

class Substring;
class SubstringComparator;
typedef set SubstringTree;

class Substring {
public:

private:
    string the_substring_;
public:
    // (...)
    static SubstringTree getAllSubstring(string main_string, int min_size);
};

3) You can use a template to delay the lookup until you have more declarations:

3)您可以使用模板来延迟查找,直到您有更多声明:

template 
struct TreeHelper
{
  typedef set Tree;
};

class Substring {
public:
  class Comparator;

private:
  string the_substring_;
public:
  // (...)
  static TreeHelper::Tree getAllSubstring(string main_string
                                             , int min_size);
};

typedef TreeHelper::Tree SubstringTree;

You can predeclare a class with this:

你可以用这个预先声明一个类:

class Foo;

Keep in mind that before the class is actually defined, you can only declare pointers to it, not instances.

请记住,在实际定义类之前,您只能声明指向它的指针,而不是实例。

forward declaration

class Substring;

I don't know if that will work for non pointer uses of Substring though.

我不知道这是否适用于Substring的非指针使用。