[英]error: Invalid use of incomplete type
I got the following problem, does anyone have a good idea? 我遇到以下问题,有人有个好主意吗?
class Vector_2d;
namespace Utils {
class Align_vector : public Vector_2d {
protected:
bool check_range(int x, int y);
public:
enum alignment {left, right, up, down};
Align_vector(Alignment alignment);
void set_alignment(Alignment alignment);
Alignment get_alignment();
};
}
the error is: 错误是:
error: invalid use of incomplete type 'class Vector_2d' 错误:无效使用不完整类型'Vector_2d类'
But how is there an error? 但是怎么会有错误呢?
class Vector_2d;
This only declares a class by that name exits. 这仅声明存在该名称的类。
To inherit from it, the full class definition needs to be available. 要从中继承,需要提供完整的类定义。
class Vector_2d {
// Your code goes here
};
class Align_vector : public Vector_2d {
// Other stuff
};
If you have separate header files for these classes, be sure to include it before defining the class that inherits. 如果这些类具有单独的头文件,请确保在定义继承的类之前将其包括在内。
#include <vector_2d.h>
namespace Utils {
class Align_vector : public Vector_2d {
// Other stuff
};
}
To put it simply, when class B
inherits from class A
, objects of class B
will have an A
sub-object as part of their layout. 简单地说,当类B
从类继承A
,该类的对象B
将有A
子对象作为其布局的一部分。
So you can't define the layout of B
, which depends on A
, if you don't have the full definition of A
. 所以,你不能定义布局B
,这取决于A
,如果你不具备的完整定义A
。
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