extract strings from C programs to
implement shared strings
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 options are as follows:
xstrto read from the standard input.
xstrwill extract the strings from the C source file or the standard input (
-), replacing string references by expressions of the form (&xstr[number]) for some number. An appropriate declaration of
xstris 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 database if they are not there already. Repeated strings and strings which are suffixes of existing strings do not cause changes to the database.
- Specify the named array in program references to abstracted strings. The default array name is “xstr”.
- Be verbose.
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
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.
The following command creates files x.c and
xs.c as before, without using or affecting any
strings file in the same directory:
$ xstr name
It may be useful to run
xstr after the C
preprocessor if any macro definitions yield strings or if there is
conditional code which contains strings which may not, in fact, be needed.
An appropriate command sequence for running
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, so that
make(1) can avoid remaking xs.o unless truly
- database of strings
- massaged C source
- C source for definition of array “xstr”
- temporary file when “xstr name” doesn't touch strings
xstr command appeared in
If a string is a suffix of another string in the database, but the
shorter string is seen first by
xstr both strings
will be placed in the database, when just placing the longer one there will