C++重定义头文件(winsock2.h)

Question

如何防止包含两次头文件？问题是我包括了在MyClass.h中然后我将MyClass.h包含在许多文件中,因此它包含多次并发生重定义错误.怎么预防？

我正在使用#pragma而不是包含警卫,我想这很好.

MyClass.h:

// MyClass.h
#pragma once

#include <winsock2.h>

class MyClass
{

// methods
public:
 MyClass(unsigned short port);
 virtual ~MyClass(void);
};

编辑:我得到的错误很少

c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(91) : warning C4005: 'AF_IPX' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(460) : see previous definition of 'AF_IPX'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(124) : warning C4005: 'AF_MAX' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(479) : see previous definition of 'AF_MAX'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(163) : warning C4005: 'SO_DONTLINGER' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(402) : see previous definition of 'SO_DONTLINGER'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(206) : error C2011: 'sockaddr' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(485) : see declaration of 'sockaddr'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(384) : error C2143: syntax error : missing '}' before 'constant'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(384) : error C2143: syntax error : missing ';' before 'constant'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(384) : error C2059: syntax error : 'constant'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(437) : error C2143: syntax error : missing ';' before '}'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(437) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(437) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(518) : warning C4005: 'IN_CLASSA' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(287) : see previous definition of 'IN_CLASSA'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(524) : warning C4005: 'IN_CLASSB' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(293) : see previous definition of 'IN_CLASSB'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(530) : warning C4005: 'IN_CLASSC' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(299) : see previous definition of 'IN_CLASSC'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(541) : warning C4005: 'INADDR_ANY' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(304) : see previous definition of 'INADDR_ANY'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(543) : warning C4005: 'INADDR_BROADCAST' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(306) : see previous definition of 'INADDR_BROADCAST'
c:\program files\microsoft sdks\windows\v6.0a\include\ws2def.h(577) : error C2011: 'sockaddr_in' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(312) : see declaration of 'sockaddr_in'
c:\program files\microsoft sdks\windows\v6.0a\include\winsock2.h(132) : error C2011: 'fd_set' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(68) : see declaration of 'fd_set'
c:\program files\microsoft sdks\windows\v6.0a\include\winsock2.h(167) : warning C4005: 'FD_SET' : macro redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(102) : see previous definition of 'FD_SET'
c:\program files\microsoft sdks\windows\v6.0a\include\winsock2.h(176) : error C2011: 'timeval' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(111) : see declaration of 'timeval'
c:\program files\microsoft sdks\windows\v6.0a\include\winsock2.h(232) : error C2011: 'hostent' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(167) : see declaration of 'hostent'
c:\program files\microsoft sdks\windows\v6.0a\include\winsock2.h(245) : error C2011: 'netent' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(180) : see declaration of 'netent'
c:\program files\microsoft sdks\windows\v6.0a\include\winsock2.h(252) : error C2011: 'servent' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(187) : see declaration of 'servent'
c:\program files\microsoft sdks\windows\v6.0a\include\winsock2.h(264) : error C2011: 'protoent' : 'struct' type redefinition
        c:\program files\microsoft sdks\windows\v6.0a\include\winsock.h(199) : see declaration of 'protoent'

Answer 1

包含<windows.h>之前包含此问题<winsock2.h>.尝试安排首先<windows.h>包含<winsock2.h>或_WINSOCKAPI_首先定义的包含列表:

#define _WINSOCKAPI_    // stops windows.h including winsock.h
#include <windows.h>
// ...
#include "MyClass.h"    // Which includes <winsock2.h>

另请参见本.

Answer 2

正如其他人所说,问题在于windows.h之前是否包括在内WinSock2.h.因为windows.h包括winsock.h.你不能同时使用WinSock2.h和winsock.h.

解决方案:

• 包括WinSock2.h之前windows.h.对于预编译头文件,您应该在那里解决它.在简单项目的情况下,很容易.但是在大型项目中(特别是在编写可移植代码时,没有预编译头文件),这可能非常困难,因为当WinSock2.h包含头文件时,windows.h可能已经包含在其他一些头文件/实现文件中.

• 定义WIN32_LEAN_AND_MEAN之前windows.h或项目范围.但它会排除你可能需要的许多其他东西,你应该自己包括它.

• 定义_WINSOCKAPI_之前windows.h或项目范围.但是,当您包含时,您将WinSock2.h获得宏重新定义警告.

• 使用windows.h而不是WinSock2.h什么时候winsock.h足够你的项目(在大多数情况下是).这可能会导致更长的编译时间,但可以解决任何错误/警告.

Answer 3

哦 - Windows的丑陋......包含的顺序在这里很重要.你需要在windows.h之前包含winsock2.h.由于windows.h可能包含在预编译头文件(stdafx.h)中,因此您需要包含winsock2.h:

#include <winsock2.h>
#include <windows.h>

Answer 4

通过使用"标题保护":

#ifndef MYCLASS_H
#define MYCLASS_H

// This is unnecessary, see comments.
//#pragma once

// MyClass.h

#include <winsock2.h>

class MyClass
{

// methods
public:
    MyClass(unsigned short port);
    virtual ~MyClass(void);
};

#endif

Answer 5

我检查递归包括，我看到的头文件，其中包括（递归地）一些#include "windows.h"和#include "Winsock.h"和写#include "Winsock2.h"。在这个文件中，我添加#include "Winsock2.h"为第一个包含。

耐心一点，一一查看include并建立这个顺序，先 #include "Winsock2.h"然后#include "windows.h"

Answer 6

当我试图拉出第三方软件包时,我遇到了这个问题,这个软件包显然包含了某些东西,其中有一些标题._WINSOCKAPI_在项目层面定义比趟过汤和修复有问题的包括更容易(更不用说更易于维护).

Answer 7

我找到了此链接windows.h和winsock2.h，它对我来说很有用：

#define _WINSOCKAPI_    // stops windows.h including winsock.h
#include <windows.h>
#include <winsock2.h>

我在查找问题发生的位置时遇到了麻烦，但是通过添加#define，我能够在不弄清楚问题的情况下进行构建。

Answer 8

在VS 2015中，以下将起作用：

#define _WINSOCKAPI_

虽然以下内容不会：

#define WIN32_LEAN_AND_MEAN

Answer 9

您应该使用标头保护。

将这些行放在头文件的顶部

#ifndef PATH_FILENAME_H
#define PATH_FILENAME_H

并在底部

#endif