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3.5.3 Style of #include statements

When including including specific header files, you need to use the ‘#include <...>’ syntax, not the ‘#include "..."’ syntax. This is true for the following POSIX or ISO C standardized header files:

• arpa/inet.h
• assert.h
• ctype.h
• dirent.h
• endian.h
• errno.h
• fcntl.h
• fenv.h
• float.h
• fnmatch.h
• glob.h
• iconv.h
• inttypes.h
• langinfo.h
• limits.h
• locale.h
• math.h
• monetary.h
• netdb.h
• net/if.h
• netinet/in.h
• poll.h
• pthread.h
• sched.h
• search.h
• signal.h
• spawn.h
• stdalign.h
• stdarg.h
• stdbit.h
• stddef.h
• stdint.h
• stdio.h
• stdlib.h
• string.h
• strings.h
• sys/msg.h
• sys/resource.h
• sys/select.h
• sys/sem.h
• sys/shm.h
• sys/socket.h
• sys/stat.h
• sys/time.h
• sys/times.h
• sys/types.h
• sys/uio.h
• sys/utsname.h
• sys/wait.h
• termios.h
• threads.h
• time.h
• uchar.h
• unistd.h
• utime.h
• wchar.h
• wctype.h

as well as for the following header files that exist in the GNU C library but are not standardized:

• alloca.h
• byteswap.h
• error.h
• getopt.h
• malloc.h
• omp.h
• pty.h
• selinux/selinux.h
• sys/file.h
• sys/ioctl.h
• sys/random.h
• sysexits.h
• utmp.h

The reason for this requirement is that for these header files, the Gnulib override uses #include_next to include the system-provided header of the same name, and #include_next may not work right with the ‘#include "..."’ syntax.