C:\Users\Jon\Documents\CDev\sandbox>gcc --version gcc (rev2, Built by MinGW-builds project) 4.8.0 Copyright (C) 2013 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. C:\Users\Jon\Documents\CDev\sandbox>gcc -Wall -o netluid.exe net_luid_test.c net_luid_test.c:18:3: error: conflicting types for 'NET_LUID' } NET_LUID; ^ In file included from c:\devkit-mb4.8.0\mingw\i686-w64-mingw32\include\iptypes.h:14:0, from c:\devkit-mb4.8.0\mingw\i686-w64-mingw32\include\iphlpapi.h:15, from net_luid_test.c:3: c:\devkit-mb4.8.0\mingw\i686-w64-mingw32\include\ifdef.h:94:3: note: previous declaration of 'NET_LUID' was here } NET_LUID, *PNET_LUID; ^ net_luid_test.c: In function 'main': net_luid_test.c:22:23: warning: unused variable 'luid' [-Wunused-variable] int main() { NET_LUID luid; return 0; } ^