ar

Purpose

     Describes common archive file format.

Synopsis

     #include <ar.h>

Description

     The ar (archive) command is used to combine several files
     into one.   The ar  command creates an  ar file.   The ld
     (link editor)  searches archive files to  resolve program
     linkage.

     Each archive begins with the archive magic string:

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

     Each archive  that contains common object  files includes
     an archive symbol  table.  See "a.out" for  the format of
     an object file.   ld uses this symbol  table to determine
     the archive members to load during the link edit process.
     The archive  symbol table,  if it  exists, is  always the
     first file  in the archive.   It is never listed,  but ar
     automatically creates and updates it.

     The archive  file members  follow the archive  header and
     symbol  table.  A  file member  follows each  file member
     header.  The format of a file member header is:

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

          struct ar_hdr {       /* file member header */
            char  ar_name[16];  /* file member name - terminated by '/'*/
            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 */
            char  ar_size[10];  /* file member size */
            char  ar_fmag[2];   /* ARFMAG - string to end header */
          };

     All information in the file member header is in printable
     ASCII.  The numeric information  contained in the headers
     is stored  as decimal  numbers, except ar_mode,  which is
     stored in octal.  Thus, if the archive contains printable
     files, you can print the archive.

     The ar_name field  is blank-padded and terminated  by a /
     (slash).  The  ar_date field indicates the  date the file

     was  last  modified prior  to  archive.   The ar  command
     allows archives to move from system to system.

     Each archive file member begins on an even-byte boundary.
     ar inserts  null bytes for  padding and a  new-line char-
     acter between files, if  necessary.  The ar_size field is
     the size  of the file  without padding.  An  archive file
     contains no empty areas.

     If the archive symbol table exists, the first file in the
     archive has  a zero-length name, for  example, ar_name[0]
     == '/'.  The contents of the symbol table are as follows:

         The number of symbols.  This is 4 bytes long.

         The  array of  offsets  into the  archive file.   The
         length is determined  by 4 bytes times  the number of
         symbols.

         The  name string  table.  The  size is  determined by
         ar_size minus  (4 bytes times (the  number of symbols
         plus 1)).

     The  sgetl  and  sputl  functions manage  the  number  of
     symbols and the array of  offsets.  The string table con-
     tains an equal number of null-terminated strings and ele-
     ments in the  offsets array.  Each offset  from the array
     associates with  the corresponding  name from  the string
     table, in order.  The string  table names all the defined
     global symbols found in the object files contained in the
     archive.  Each offset locates  the archive header for the
     associated symbol.

Related Information

     In this book:  "sgetl, sputl" and "a.out."

     The ar,  ld, and strip  commands in AIX  Operating System
     Commands Reference.