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)