xstr(CP)                       6 January 1993                       xstr(CP)


 Name

    xstr - extracts strings from C programs

 Syntax

    xstr [-c] [-] [ file ]

 Description

    xstr maintains a file, strings, into which strings in component parts of
    a large program are hashed.  These strings are replaced with references
    to this common area.  This serves to implement shared constant strings,
    most useful if they are also read-only.

    The command

       xstr -c name

    will extract the strings from the C source in name, replacing string
    references by expressions of the form (&xstr[number]) for some number.
    An appropriate declaration of xstr is prepended to the file.  The result-
    ing C text is placed in the file x.c, to then be compiled.  The strings
    from this file are placed in the strings data base if they are not there
    already.  Repeated strings and strings which are suffices of existing
    strings do not cause changes to the data base.

    After all components of a large program have been compiled, a file xs.c
    declaring the common xstr space can be created by a command of the form

       xstr name1 name2 name3 ...

    This xs.c file should then be compiled and loaded with the rest of the
    program.  If possible, the array can be made read-only (shared) saving
    space and swap overhead.

    xstr can also be used on a single file.  A command

       xstr name

    creates files x.c and xs.c as before, without using or affecting any
    strings file in the same directory.

    It may be useful to run xstr after the C preprocessor if any macro defin-
    itions yield strings or if there is conditional code which contains
    strings which may not, in fact, be needed.  xstr reads from its standard
    input when the argument ``-'' is given.  An appropriate command sequence
    for running xstr after the C preprocessor is:

       cc -E name.c | xstr -c -
       cc -c x.c
       mv x.o name.o


    xstr does not touch the file strings unless new items are added, thus
    make can avoid remaking xs.o unless truly necessary.

 Files


    strings   Data base of strings.

    x.c       Massaged C source.

    xs.c      C source for definition of array xstr.

    /tmp/xs*  Temp file when xstr name doesn't touch strings.

 Notes

    If a string is a suffix of another string in the data base, but the
    shorter string is seen first by xstr, both strings will be placed in the
    data base when just placing the longer one there will do.

 See also

    mkstr(CP)

 Standards conformance

    This utility was developed at the University of California at Berkeley
    and is used with permission.