Question

I use Ubuntu(Linux)+ gcc as a example.

• stdio.h
• sys/socket.h
• poll.h
• pthread.h

which on Ubuntu Linux(with gcc installed), are respectively provided by which organization? GNU? Linux ? ISO? Ubuntu?

And what about the corresponding library?

Answer 1

These are library headers that are part of C library installed on your system.

On Ubuntu glibc implementation is used (GNU C library).
Some other examples of C libraries:
uclibc (embedded), avr-libc (embedded), dietlibc, klibc, elibc_FreeBSD …

ISO/IEC has created standard and these libraries follow it.

~ head -n 20 /usr/include/stdio.h
/* Define ISO C stdio on top of C++ iostreams.
   Copyright (C) 1991, 1994-2010, 2011 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */