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xstr(1)			  BSD General Commands Manual		       xstr(1)


NAME

     xstr - extract strings from C programs to implement shared strings


SYNOPSIS

     xstr [-c] [-l array] [-] [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.

     Available options:

     -	     xstr reads from the standard input.

     -c	     xstr will extract the strings from the C source file or the stan-
	     dard input (-), replacing string references by expressions of the
	     form (&xstr[number]) for some number.  An appropriate declaration
	     of xstr is prepended to the file.	The resulting 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 suffixes of
	     existing strings do not cause changes to the data base.

     -l array
	     Specify the named array in program references to abstracted
	     strings.  The default array name is xstr.

     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

     The file xs.c 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 defi-
     nitions yield strings or if there is conditional code which contains
     strings which may not, in fact, be needed.	 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(1) 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


SEE ALSO

     mkstr(1)


BUGS

     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.


HISTORY

     The xstr command appeared in 3.0BSD.

3rd Berkeley Distribution      December 30, 1993     3rd Berkeley Distribution

Mac OS X 10.3 - Generated Sun Feb 24 08:58:14 CST 2008
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