XSTR(1) User Commands XSTR(1)

NAME

xstr - extract strings from C programs to implement shared strings

SYNOPSIS

xstr -c filename [-v] [-l array]


xstr [-l array]


xstr filename [-v] [-l array]

DESCRIPTION

xstr maintains a file called 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, which are most useful if they are also read-only.


The command:

example% xstr -c filename


extracts 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
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.


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

example% xstr


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:


example% xstr filename


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

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


xstr does not touch the file strings unless new items are added; thus
make(1S) can avoid remaking xs.o unless truly necessary.

OPTIONS

-c filename
Take C source text from filename.


-v
Verbose: display a progress report indicating where
new or duplicate strings were found.


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

FILES

strings
data base of strings


x.c
massaged C source


xs.c
C source for definition of array "xstr*(rq


/tmp/xs*
temp file when xstr filename doesn't touch strings

SEE ALSO

make(1S), attributes(7)

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 would do.

NOTES

Be aware that xstr indiscriminately replaces all strings with
expressions of the form &xstr[number] regardless of the way the
original C code might have used the string. For example, you will
encounter a problem with code that uses sizeof() to determine the
length of a literal string because xstr will replace the literal
string with a pointer that most likely will have a different size
than the string's. To circumvent this problem:

o use strlen() instead of sizeof(); note that sizeof()
returns the size of the array (including the null byte at
the end), whereas strlen() doesn't count the null byte.
The equivalent of sizeof("xxx") really is
(strlen("xxx"))+1.

o use #define for operands of sizeof() and use the define'd
version. xstr ignores #define statements. Make sure you
run xstr on filename before you run it on the
preprocessor.


You will also encounter a problem when declaring an initialized
character array of the form

char x[] = "xxx";


xstr will replace xxx with an expression of the form &xstr[number]
which will not compile. To circumvent this problem, use static char
*x = "xxx" instead of static char x[] = "xxx".

September 14, 1992 XSTR(1)