问题描述：在 VC 6.0中使用socket相关的函数时没有什么问题，可是到了.net下就有以下类似的错误，
[C++ Error] winsock2.h(109): E2238 Multiple declaration
for 'fd_set'
[C++ Error] winsock.h(54): E2344 Earlier declaration of
'fd_set'
[C++ Error] winsock2.h(112): E2146 Need an identifier to
declare
[C++ Warning] winsock2.h(144): W8017 Redefinition of 'FD_SET' is not
identical
[C++ Error] winsock2.h(153): E2238 Multiple declaration for
'timeval'
[C++ Error] winsock.h(97): E2344 Earlier declaration of
'timeval'
[C++ Error] winsock2.h(209): E2238 Multiple declaration for
'hostent'
[C++ Error] winsock.h(153): E2344 Earlier declaration of
'hostent'
[C++ Error] winsock2.h(222): E2238 Multiple declaration for
'netent'
[C++ Error] winsock.h(166): E2344 Earlier declaration of
'netent'
[C++ Error] winsock2.h(229): E2238 Multiple declaration for
'servent'
[C++ Error] winsock.h(173): E2344 Earlier declaration of
'servent'
[C++ Error] winsock2.h(241): E2238 Multiple declaration for
'protoent'
[C++ Error] winsock.h(185): E2344 Earlier declaration of
'protoent'
[C++ Error] winsock2.h(327): E2238 Multiple declaration for
'in_addr'
[C++ Error] winsock.h(269): E2344 Earlier declaration of
'in_addr'
[C++ Error] winsock2.h(385): E2238 Multiple declaration for
'sockaddr_in'
[C++ Error] winsock.h(319): E2344 Earlier declaration of
'sockaddr_in'
[C++ Error] winsock2.h(395): E2238 Multiple declaration for
'WSAData'
[C++ Error] winsock.h(329): E2344 Earlier declaration of
'WSAData'
[C++ Error] winsock2.h(411): E2146 Need an identifier to
declare
[C++ Warning] winsock2.h(455): W8017 Redefinition of 'SO_DONTLINGER'
is not identical
[C++ Warning] winsock2.h(512): W8017 Redefinition of
'AF_IPX' is not identical
[C++ Warning] winsock2.h(540): W8017 Redefinition
of 'AF_MAX' is not identical
[C++ Error] winsock2.h(546): E2238 Multiple
declaration for 'sockaddr'
[C++ Error] winsock.h(492): E2344 Earlier
declaration of 'sockaddr'
[C++ Error] winsock2.h(586): E2238 Multiple
declaration for 'sockproto'
[C++ Error] winsock.h(501): E2344 Earlier
declaration of 'sockproto'
[C++ Error] winsock2.h(625): E2238 Multiple
declaration for 'linger'
[C++ Error] winsock2.h(625): E2228 Too many error or
warning messages
Solution：
This problem arises because windows.h (at
least, that version of it) includes not winsock2.h but winsock.h;
sadly when Microsoft wrote winsock2.h they chose
neither to change windows.h to include winsock2.h, which replaces winsock.h, nor to include windows.h from winsock2.h
and then add the definitions for the new Winsock 2 API methods & structures
(this might seem reasonable since Winsock 2 does, strictly speaking, replace
Winsock 1, but since the API must be fully backwards-compatible the distinction
is somewhat meaningless and there's no real benefit to making winsock2.h standalone).
The fix is thankfully simple: always "#include <winsock2.h>" before windows.h.
However, you must remember that if windows.h
has been included by (for example) a higher-level header file that is
subsequently including your header file, it's too late - so you must make sure
that the higher-level header files respect this convention also.
It is however rarely necessary to modify the header files of libraries or
other code modules you are using just because you include
their header files, and their header files include windows.h - you can just include winsock2.h before you include the library's header
files.
在包含jrtplib有时候我也遇到这个问题，解决方法与之相同。一句话，在#include<windows.h>之前 #include
<winsock2.h> 问题就可以解决。
问题描述]
在包含了<windows.h>以及<winsock2.h>的工程中,编译有时会出现如
下错误:
error C2011: 'fd_set' : 'struct' type redefinition
error
C2011: 'timeval' : 'struct' type redefinition
....
error C2375: 'accept' : redefinition; different
linkage
[原因分析]
主要原因是因为<windows.h>中包含了<winsock.h>头文件,由于其版
本的不同，导致出现上述的错误。<windows.h>中相关代码如下:
#ifndef
WIN32_LEAN_AND_MEAN
#include <cderr.h>
#include <dde.h>
#include
<ddeml.h>
........
#ifndef
_MAC
#include <winperf.h>
#include
<winsock.h>
#endif
.......
#include
<commdlg.h>
#endif
#endif
[解决方案]
由以上代码可以看出如果在没有定义WIN32_LEAN_AND_MEAN宏的大前
提下windows.h有可能包含winsock.h 头文件，因此我们得出一个很简单
的解决方法就是在包含<windows.h>之前定义WIN32_LEAN_AND_MEAN宏,如
下所示:
#define
WIN32_LEAN_AND_MEAN
#include
<windows.h>