I am trying to compile some source code in cygwin (in windows 7) and get the following error when I run the make file g++ -DHAVE_CONFIG_H -I. -I.. -I.. -Wall -Wextra -Werror -g -O2 -MT libcommon_a Fcntl.o -MD -MP -MF .deps/libcommon_a-Fcntl.Tpo -c -o libcommon_a-Fcntl.o `test -f 'Fcntl.cpp' || echo './'`Fcntl.cpp Fcntl.cpp: In function int setCloexec(int): Fcntl.cpp:8: error: 'F_GETFD' was not declared in this scope Fcntl.cpp:8: error: 'fcntl' was not declared in this scope Fcntl.cpp:11: error: 'FD_CLOEXEC' was not declared in this scope Fcntl.cpp:12: error: 'F_SETFD' was not declared in this scope make[4]: *** [libcommon_a-Fcntl.o] Error 1 make[4]: Leaving directory `/abyss-1.1.2/Common' make[3]: *** [all-recursive] Error 1 make[3]: Leaving directory `/abyss-1.1.2' make[2]: *** [all] Error 2 make[2]: Leaving directory `/abyss-1.1.2' make[1]: *** [.build-conf] Error 2 make[1]: Leaving directory `/cygdrive/c/Users/Martin/Documents/NetBeansProjects/abyss-1.1.2_1' make: *** [.build-impl] Error 2 The problem file is:- #include "Fcntl.h" #include <fcntl.h> /* Set the FD_CLOEXEC flag of the specified file descriptor. */ int setCloexec(int fd) { int flags = fcntl(fd, F_GETFD, 0); if (flags == -1) return -1; flags |= FD_CLOEXEC; return fcntl(fd, F_SETFD, flags); } I don't understand what is going on, the file fcntl.h is available and the varaiables that it says were not declared in this scope do not give an error when I compile the file on its own Any help would be much appreciated Many Thanks