virtual 在类外使用

[xuegao007]

#ifndef DBDIMVAR_H
#define DBDIMVAR_H
//
// (C) Copyright 1993-2006 by Autodesk, Inc.
//
// Permission to use, copy, modify, and distribute this software in
// object code form for any purpose and without fee is hereby granted,
// provided that the above copyright notice appears in all copies and
// that both that copyright notice and the limited warranty and
// restricted rights notice below appear in all supporting
// documentation.
//
// AUTODESK PROVIDES THIS PROGRAM "AS IS" AND WITH ALL FAULTS.
// AUTODESK SPECIFICALLY DISCLAIMS ANY IMPLIED WARRANTY OF
// MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. AUTODESK, INC.
// DOES NOT WARRANT THAT THE OPERATION OF THE PROGRAM WILL BE
// UNINTERRUPTED OR ERROR FREE.
//
// Use, duplication, or disclosure by the U.S. Government is subject to
// restrictions set forth in FAR 52.227-19 (Commercial Computer
// Software - Restricted Rights) and DFAR 252.227-7013(c)(1)(ii)
// (Rights in Technical Data and Computer Software), as applicable.
//
//
// DESCRIPTION:
// The api for dimensioning variables shared by
// AcDbDatabase,
// AcDbDimstyleTableRecord, and
// AcDbDimension

// ------------------------- Dimension Style get methods
//
virtual int dimadec () const; // new to R15
virtual bool dimalt () const;
virtual int dimaltd () const;
virtual double dimaltf () const;
...
...
#endif // ifndef DBDIMVAR_H
----------------------------------------------------------------------------
以上代码是在一个.h文件中.文件中的函数全是virtual这样的.没有类的存在.
小弟不明白这个virtual是怎么用的

[liuhao159753]

后面的子类里面按实际情况具体实现它，上面不是纯虚，也可以再当前类里面实现~~

[xingzhe2001]

因为这个头文件他会在类里面include,所以就相当于定义到类里面一样。

[sj13426074890]

学习了

[nwao7890]

應該是這個文件會被其它 不同的頭文件包含，跟2樓說的一樣

[xuegao007]

正如2,4楼所说的一样.
谢谢大家