ar(FP)                         6 January 1993                         ar(FP)


 Name

    ar - archive file format

 Description

    The archive command ar is used to combine several files into one.
    Archives are used mainly as libraries to be searched by the link editor
    ld(CP).

    A file produced by ar has a magic number at the start, followed by the
    constituent files, each preceded by a file header.  The magic number
    string is in a portable archive format that uses the ASCII string:

       !<arch>\n

    The header of each file is declared in /usr/include/ar.h.

    Each file begins on a word boundary; a null byte is inserted between
    files if necessary.  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.

 Notes

    The ar(CP) utility now handles filenames longer than 14 characters so
    that the upper limit for the filename component is 512 characters and the
    limit for a full pathname is 1024 characters.

    Files with long filenames are stored in the archive using a short
    filename convention: LNGFILxxxxxx. Where the xxxxxx is an ASCII-encoded
    decimal serial number, for example, _LNGFIL000001 and _LNGFIL000002.
    These shortened filenames are used to identify the long filenames by tak-
    ing the serial numbers and using them as indexes into a map table of long
    filenames.  Because of the encoding, up to 1,000,000 long filenames can
    be stored in an archive.

    A table containing the mapping information on long filenames (called the
    maptable) is stored in the archive as a regular (archived) file. This
    file (called the mapfile) is either the first or the second file in the
    archive depending on whether the archive file has a symbol table file or
    not. This mapfile is part of the archive if (and only if) there are files
    with long filenames.

    If there are any COFF files in the archive, the first archive member is
    the symbols table.  If there are any files with long filenames, the map-
    file is the next file after the symbol table.

    The format of the long filenames table is:

       <stringnumber><seriallength><string>


    Where:

    +  <stringnumber> is a 7-byte numeric ASCII string

    +  <seriallength> is a 7-byte numeric ASCII string

    +  <string> is a string of stringlength characters long.

    An example entry is:

       00000190000001longfilenamemapfile

    The string length is 19 characters, the serial number entry is 1, and the
    string is longfilenamemapfile.

 See also

    ar(CP), ar(S), ld(CP)