Hi, My project uses boost 1.34.1 libraries for asio and also includes windows.h (which in turn includes winsock.h). This results in a macro redefinition error for FD_SETSIZE and then goes on to spew a bucketload of related errors. The easiest way to reproduce this is to have a simple main.cpp with just: #include<boost/asio.hpp> #include<windows.h> int main() { return 0; } Any ideas on what I'm doing wrong? Or what I could try? I've tried defining WIN32_LEAN_AND_MEAN, IPPROTO_V6 in the makefile, but to no avail. I'm using VC 8 on a windows XP. ======================== My comand line looks like this: C:\perforce\some\path\>make main.o -- Compile main.cpp... c:/perforce/toolchain/win32/winsdk-6.1.6000/VC/bin/cl.exe -nologo -Fdc:/perforce/some/path somelib.pdb -Gm -EHsc -c -Zi -TP -GR -D_WIN32 -D_USRDLL -D_WIN32_WINNT -DWINVER=0x0600 -D_WINDLL -D_MBCS -W3 -D_CRT_NO NSTDC_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -DUSERLEVEL -MDd -Od -D_DEBUG -RTC1 -I"C:\perforce\toolchain\win32\boost-1.34.1\include" -Ic:/perforce/toolchain/win32/winsdk-6.1.6000/Include -Ic:/perforce/toolchain/win32/winsdk-6.1.6000/VC/include -Ic:/perforce/toolchain/win32/winsdk-6.1.6000/VC/PlatformSDK/Include And the error message looks like: C:\perforce\toolchain\win32\boost-1.34.1\include\boost/asio/detail/socket_types.hpp(44) : warning C4005: 'FD_SETSIZE' : macro redefinition c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\winsock.h(65) : see previous definition of 'FD_SETSIZE' c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\ws2def.h(91) : warning C4005: 'AF_IPX' : macro redefinition c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\winsock.h(460) : see previous definition of 'AF_IPX' c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\ws2def.h(116) : warning C4005: 'AF_MAX' : macro redefinition c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\winsock.h(479) : see previous definition of 'AF_MAX' c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\ws2def.h(163) : warning C4005: 'SO_DONTLINGER' : macro redefinition c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\winsock.h(402) : see previous definition of 'SO_DONTLINGER' c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\ws2def.h(206) : error C2011: 'sockaddr' : 'struct' type redefinition c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\winsock.h(485) : see declaration of 'sockaddr' c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\ws2def.h(384) : error C2143: syntax error : missing '}' before 'constant' c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\ws2def.h(437) : error C2143: syntax error : missing ';' before '}' c:\perforce\toolchain\win32\winsdk-6.1.6000\Include\ws2def.h(437) :error C4430: missing type specifier - int assumed. Note: C++ does not support default-int ========================