XSTR(1) | General Commands Manual | XSTR(1) |
xstr
—
xstr |
[-cv ] [-l
array] [- ]
[file ...] |
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 standard 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-v
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.
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 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.
xstr
command appeared in
3.0BSD.
xstr
both strings will be
placed in the data base, when just placing the longer one there will do.
xstr
does not parse the file properly so
it does not know not to process:
char var[] = "const";
char var[] = (&xstr[N]);
These must be changed manually into an appropriate initialization for the string, or use the following ugly hack.
Also, xstr
cannot initialize structures
and unions that contain strings. Those can be fixed by changing from:
struct foo { int i; char buf[10]; } = { 1, "foo" };
struct foo { int i; char buf[10]; } = { 1, { 'f', 'o', 'o', '\0' } };
The real problem in both cases above is that the compiler knows
the size of the literal constant so that it can perform the initialization
required, but when xstr
changes the literal string
to a pointer reference, the size information is lost. It would require a
real parser to do this right, so the obvious solution is to fix the program
manually to compile, or even better rely on the compiler and the linker to
merge strings appropriately.
Finally, xstr
is not very useful these
days because most of the string merging is done automatically by the
compiler and the linker, provided that the strings are identical and
read-only.
July 23, 2004 | NetBSD 9.0 |