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AR.H(3HEAD)							   AR.H(3HEAD)

NAME
       ar.h, ar - archive file format

SYNOPSIS
       #include <ar.h>

DESCRIPTION
       The  archive command ar is used to combine several files into one.  Ar‐
       chives are used mainly as libraries to be searched by the  link	editor
       ld.

       Each archive begins with the archive magic string.

	 #define  ARMAG	  "!<arch>\n"	 /* magic string */
	 #define  SARMAG   8		 /* length of magic string */

       Following  the  archive magic string are the archive file members. Each
       file member is preceded by a file member header which is of the follow‐
       ing format:

	 #define  ARFMAG   "`\n"	 /* header trailer string */

	 struct	 ar_hdr			 /* file member header */
	 {
	     char    ar_name[16];	 /* '/' terminated file member name */
	     char    ar_date[12];	 /* file member date */
	     char    ar_uid[6]		 /* file member user identification */
	     char    ar_gid[6]		 /* file member group identification */
	     char    ar_mode[8]		 /* file member mode (octal) */
	     char    ar_size[10];	 /* file member size */
	     char    ar_fmag[2];	 /* header trailer string */
	 };

       All  information	 in the file member headers is in printable ASCII. The
       numeric information contained in the headers is stored as decimal  num‐
       bers  (except for ar_mode which is in octal). Thus, if the archive con‐
       tains printable files, the archive itself is printable.

       If the file member name fits,  the  ar_name  field  contains  the  name
       directly,  and  is  terminated by a slash (/) and padded with blanks on
       the right. If the member's name does not fit, ar_name contains a	 slash
       (/)  followed  by  a decimal representation of the name's offset in the
       archive string table described below.

       The ar_date field is the modification date of the file at the  time  of
       its  insertion  into  the  archive. Common format archives can be moved
       from system to system as long as the portable  archive  command	ar  is
       used.

       Each  archive file member begins on an even byte boundary; a newline is
       inserted between files  if  necessary.  Nevertheless,  the  size	 given
       reflects the actual size of the file exclusive of padding.

       Notice there is no provision for empty areas in an archive file.

       Each archive that contains object files (see  a.out(4)) includes an ar‐
       chive symbol table. This symbol table is used by the link editor	 ld to
       determine  which	 archive  members  must be loaded during the link edit
       process.	 The archive symbol table (if it exists) is always  the	 first
       file  in the archive (but is never listed) and is automatically created
       and/or updated by  ar.

       The archive symbol table has a zero length name (that  is,   ar_name[0]
       is  '/'),   ar_name[1]=='  ', etc.). All ``words'' in this symbol table
       have four bytes, using the machine-independent  encoding	 shown	below.
       All machines use the encoding described here for the symbol table, even
       if the machine's ``natural'' byte order is different.

			  0	  1	  2	  3
	 0x01020304	  01	  02	  03	  04

       The contents of this file are as follows:

	   1.	  The number of symbols.  Length: 4 bytes.

	   2.	  The array of offsets into the archive file.  Length: 4 bytes
		  * ``the number of symbols''.

	   3.	  The  name  string table.  Length: ar_size - 4 bytes * (``the
		  number of symbols'' + 1).

       As an example, the following symbol table defines 4  symbols.  The  ar‐
       chive  member  at  file	offset 114 defines name. The archive member at
       file offset 122 defines object. The archive member at file  offset  426
       defines	function  and  the  archive  member at file offset 434 defines
       name2.

   Example Symbol Table
	 Offset	    +0	 +1   +2   +3
		   ___________________
	  0	  |	    4	      | 4 offset entries
		  |___________________|
	  4	  |	  114	      | name
		  |___________________|
	  8	  |	  122	      | object
		  |___________________|
	 12	  |	  426	      | function
		  |___________________|
	 16	  |	  434	      | name2
		  |___________________|
	 20	  |  n | a  | m	 | e  |
		  |____|____|____|____|
	 24	  | \0 | o  | b	 | j  |
		  |____|____|____|____|
	 28	  |  e | c  | t	 | \0 |
		  |____|____|____|____|
	 32	  |  f | u  | n	 | c  |
		  |____|____|____|____|
	 36	  |  t | i  | o	 | n  |
		  |____|____|____|____|
	 40	  | \0 | n  | a	 | m  |
		  |____|____|____|____|
	 44	  |  e | 2  | \0 |    |
		  |____|____|____|____|

       The string table contains exactly as many null  terminated  strings  as
       there  are elements in the offsets array. Each offset from the array is
       associated with the  corresponding  name	 from  the  string  table  (in
       order).	The  names in the string table are all the defined global sym‐
       bols found in the common object files in the archive.  Each  offset  is
       the location of the archive header for the associated symbol.

       If some archive member's name is more than 15 bytes long, a special ar‐
       chive member contains a table of file names, each followed by  a	 slash
       and a new-line.	This string table member, if present, will precede all
       ``normal'' archive members. The special archive symbol table is	not  a
       ``normal'' member, and must be first if it exists. The ar_name entry of
       the  string  table's  member  header   holds   a	  zero	 length	  name
       ar_name[0]=='/', followed by one trailing slash (ar_name[1]=='/'), fol‐
       lowed by blanks (ar_name[2]==' ', etc.). Offsets into the string	 table
       begin  at  zero.	 Example  ar_name values for short and long file names
       appear below.

	 Offset	  +0   +1   +2	 +3   +4   +5	+6   +7	  +8   +9
		__________________________________________________
	  0	| f  | i  | l  | e  | _	 | n  | a  | m	| e  | _  |
		|____|____|____|____|____|____|____|____|____|____|
	 10	| s  | a  | m  | p  | l	 | e  | /  | \n | l  | o  |
		|____|____|____|____|____|____|____|____|____|____|
	 20	| n  | g  | e  | r  | f	 | i  | l  | e	| n  | a  |
		|____|____|____|____|____|____|____|____|____|____|
	 30	| m  | e  | x  | a  | m	 | p  | l  | e	| /  | \n |
		|____|____|____|____|____|____|____|____|____|____|

	    Member Name				   ar_name
	 _______________________________________________________________
	 short-name	      | short-name/  | Not in string table
			      |		     |
	 file_name_sample     | /0	     | Offset 0 in string table
			      |		     |
	 longerfilenamexample | /18	     | Offset 18 in string table
	 _____________________|______________|___________________________

SEE ALSO
       ar(1), ld(1), strip(1), a.out(4)

NOTES
       The strip utility will remove  all  archive  symbol  entries  from  the
       header.	 The  archive  symbol  entries	must  be restored with the -ts
       options of the ar command before the archive can be used with the  link
       editor ld.

				  Jul 1, 1998			   AR.H(3HEAD)
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