Editing Ar (Unix) (section)

====System V (or GNU) variant====
System V ar uses a '/' character (0x2F) to mark the end of the filename; this allows for the use of spaces without the use of an extended filename.  Then it stores multiple extended filenames in the data section of a file with the name "//", this record is referred to by future headers. A header references an extended filename by storing a "/" followed by a decimal offset to the start of the filename in the extended filename data section.  The format of this "//" file itself is simply a list of the long filenames, each separated by one or more LF characters.  Note that the decimal offsets are number of characters, not line or string number within the "//" file. This is usually the second entry of the file, after the symbol table which always is the first.

System V ar uses the special filename "/" to denote that the following data entry contains a symbol lookup table, which is used in ar libraries to speed up access.  This symbol table is built in three parts which are recorded together as contiguous data.

# A 32-bit big endian integer, giving the number of entries in the table.
# A set of 32-bit big endian integers. One for each symbol, recording the position within the archive of the header for the file containing this symbol.
# A set of Zero-terminated strings.  Each is a symbol name, and occurs in the same order as the list of positions in part 2.

Some System V systems do not use the format described above for the symbol lookup table.
For operating systems such as [[HP-UX]] 11.0, this information is stored in a data structure based on the [[System Object Model (file format)|SOM]] file format.

The special file "/" is not terminated with a specific sequence; the end is assumed once the last symbol name has been read.

To overcome the 4 GiB file size limit some operating system like [[Solaris (operating system)|Solaris]] 11.2 and GNU use a variant lookup table. Instead of 32-bit integers, 64-bit integers are used in the symbol lookup tables. The string "/SYM64/" instead "/" is used as identifier for this table<ref name="ar64bit">{{cite web|title=ar.h(3HEAD)|url=https://docs.oracle.com/cd/E36784_01/html/E36873/ar.h-3head.html|work=docs.oracle.com|publisher=Oracle Corporation|date=11 November 2014|access-date=14 November 2018}}</ref>

===== Windows variant =====
The Windows (PE/COFF) variant is based on the SysV/GNU variant. The first entry "/" has the same layout as the SysV/GNU symbol table. The second entry is another "/", a Microsoft extension that stores an extended symbol cross-reference table. This one is sorted and uses little-endian integers.<ref name="Levine99"/><ref>{{Citation
 |url=http://www.microsoft.com/msj/0498/hood0498.aspx
 |first=Matt |last=Pietrek |author-link=Matt Pietrek
 |title=Under The Hood
 |work=Microsoft Systems Journal
 |date=April 1998
 |access-date=2014-08-23
 |archive-url=https://web.archive.org/web/20070624034732/https://www.microsoft.com/msj/0498/hood0498.aspx
 |archive-date=2007-06-24
}}</ref> The third entry is the optional "//" long name data as in SysV/GNU.<ref>{{cite web |title=llvm-mirror/llvm: archive.cpp (format detection) |url=https://github.com/llvm-mirror/llvm/blob/ad1310e/lib/Object/Archive.cpp#L593-L610 |website=GitHub |access-date=10 February 2020 |language=en}}</ref>