“class”类型重定义,include(头文件)重复加载 QT /c++

谁践踏了优雅 2022-09-18 08:57 179阅读 0赞

提示报错："class”类型重定义

**原因1**：include 头文件重复加载

**原因2**：两个类相互include

解决：

**1.include  头文件重复加载**

在include之前添加

<table style="border-width:0px!important; margin:0px!important; padding:0px!important; left:auto!important; top:auto!important; width:auto!important; height:auto!important; text-align:left!important; right:auto!important; bottom:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; font-style:normal!important; vertical-align:baseline!important; float:none!important; border-collapse:collapse!important; position:static!important; min-height:inherit!important; outline-width:0px!important"> 
 <tbody style="border-width:0px!important; margin:0px!important; padding:0px!important; left:auto!important; top:auto!important; width:auto!important; height:auto!important; text-align:left!important; right:auto!important; bottom:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; font-style:normal!important; vertical-align:baseline!important; float:none!important; position:static!important; min-height:inherit!important; outline-width:0px!important"> 
  <tr style="border-width:0px!important; margin:0px!important; padding:0px!important; left:auto!important; top:auto!important; width:auto!important; height:auto!important; text-align:left!important; right:auto!important; bottom:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; font-style:normal!important; vertical-align:baseline!important; float:none!important; position:static!important; min-height:inherit!important; outline-width:0px!important"> 
   <td style="border-width:0px!important; margin:0px!important; padding:0px!important; left:auto!important; top:auto!important; width:3em!important; height:auto!important; text-align:left!important; right:auto!important; bottom:auto!important; color:rgb(175,175,175)!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; font-style:normal!important; vertical-align:top!important; float:none!important; position:static!important; min-height:inherit!important; outline-width:0px!important"> <code style="border-width:0px!important; margin:0px!important; padding:0px 0.3em 0px 0px!important; left:auto!important; top:auto!important; width:2.7em!important; height:auto!important; text-align:right!important; right:auto!important; bottom:auto!important; color:rgb(78,99,132); line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; font-style:normal!important; font-variant:normal; font-weight:normal; vertical-align:baseline!important; float:none!important; display:block!important; position:static!important; min-height:inherit!important; outline-width:0px!important">1</code></td> 
   <td style="border-width:0px 0px 0px 3px!important; margin:0px!important; padding:0px 0px 0px 0.5em!important; left:auto!important; top:auto!important; width:auto!important; height:auto!important; text-align:left!important; right:auto!important; bottom:auto!important; color:rgb(0,0,0)!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; font-style:normal!important; vertical-align:top!important; border-left-color:rgb(108,226,108)!important; border-left-style:solid!important; float:none!important; position:static!important; min-height:inherit!important; outline-width:0px!important"> <code style="border-width:0px!important; margin:0px!important; padding:0px!important; left:auto!important; top:auto!important; width:auto!important; height:auto!important; text-align:left!important; right:auto!important; bottom:auto!important; color:gray!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; font-style:normal!important; font-variant:normal; font-weight:normal; vertical-align:baseline!important; float:none!important; display:block; position:static!important; min-height:inherit!important; outline-width:0px!important">#pragma once</code></td> 
  </tr> 
 </tbody> 
</table>

意思是只include一次就可以了。

**原因2：两个类相互include**

系统那些头文件，无论怎么include都没事，因为一般都用了宏定义，防止重复。

在头文件最上方写：

\#ifndef  AA (一个名字，尽量做到唯一）

\#define AA(跟上边的名字一样）

文件最后写：

\#endif

两个类之间互相引用：

**\[cpp\]** [ view plain][view plain] [copy][view plain] [print][view plain] [?][view plain]

1.  A.H：  
2.    
3.  class A\{  
4.    
5.  B\* b;  
6.    
7.  \}  
8.    
9.  B.H：  
10.   
11. class B\{  
12.   
13. A\* b;  
14.   
15. \}

A.H：
    
    class A{
    
    B* b;
    
    }
    
    B.H：
    
    class B{
    
    A* b;
    
    }

就这样互相include后，肯定会出错。

需要在各自的声明前边，加上对方的声明，变成：

**\[cpp\]** [ view plain][view plain] [copy][view plain] [print][view plain] [?][view plain]

1.  A.H：  
2.    
3.  class B;  
4.    
5.  class A\{  
6.    
7.  B\* b;  
8.    
9.  \}  
10.   
11. B.H：  
12.   
13. class A;  
14.   
15. class B\{  
16.   
17. A\* b;  
18.   
19. \}

[view plain]: http://blog.csdn.net/ymc0329/article/details/7284503#