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## Howto write a Hurd library

Build the Hurd sources:
------------------------
 
Refer to: [[HurdCompilation]]

Create the library files:
----------------------

Create a directory, say, libhello in the Hurd sources directory. 

Create a lhello.h header file:

<pre>
/* lhello.h - Example library header file.
   Copyright (C) 2006 Free Software Foundation, Inc.
   Written by Shakthi Kannan <shaks@shakthimaan.com>.

   This file is part of the GNU Hurd.

   The GNU Hurd is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2, or (at
   your option) any later version.

   The GNU Hurd 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
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with the GNU Hurd; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

#ifndef _HURD_HELLO_H
#define _HURD_HELLO_H	1

struct hello
{
  int x;
};

#endif	/* _HURD_HELLO_H */
</pre>

Replace filename, year, author name and e-mail address appropriately.

Create a lhello.c file:

<pre>
/* lhello.c - Example library .c file.
   Copyright (C) 2006
   Free Software Foundation, Inc.
   Written by Shakthi Kannan <shaks@shakthimaan.com>.
   
   This file is part of the GNU Hurd.

   The GNU Hurd is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   The GNU Hurd 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with the GNU Hurd; see the file COPYING.  If not, write to
   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

#include "lhello.h"

void 
print_hello (void)
{
  struct hello example;
  example.x = 2;
  printf ("foo and bar are %d words!\n", example.x);
} 
</pre>

Replace header file year, author name and e-mail address appropriately.

Create a Makefile

<pre>
#
#   Copyright (C) 2006 Free Software Foundation, Inc.
#
#   This file is part of the GNU Hurd.
#
#   The GNU Hurd is free software; you can redistribute it and/or
#   modify it under the terms of the GNU General Public License as
#   published by the Free Software Foundation; either version 2, or (at
#   your option) any later version.
#
#   The GNU Hurd 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
#   General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with this program; if not, write to the Free Software
#   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

dir := libhello
makemode := library

libname := libhello
SRCS = lhello.c
installhdrs = lhello.h
LCLHDRS = $(installhdrs)

OBJS = $(SRCS:.c=.o)

include ../Makeconf
</pre>

Update the Makeconf file:

Add libhello to lib-subdirs target in the top-level Makefile in the Hurd sources.

<pre>
cd build
../configure
make
</pre>

Testing the library
-------------------

Write a file, say, foo.c:

<pre>
/* foo.c */

#define _GNU_SOURCE

int
main (int argc, char *argv[])
{
  print_hello();
  return 0;
}
</pre>

Static compilation and linking method:

<pre>
gcc -g -o foo foo.c -L/path/to/libhello -lhello -static
</pre>

Run the example:

<pre>
./foo
</pre>

Compilation and dynamic linking method:

<pre>
LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path/to/libhello
gcc -g -o foo foo.c -L/path/to/libhello -lhello
</pre>

where /path/to/libhello = /path/to/hurd/build/libhello

Run the example:
<pre>
./foo
</pre>

-- ShakthiKannan - 30 Nov 2006