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[10]Interesting internationalization
Posted on September 18, 2008
Filed Under [11]Programming |
I've been having a rather enjoyable discussion with [12]Lorenzo
Bettini, the author of GNU [13]Gengetopt and [14]Gengen. If you are not
familiar with Gengetopt, its a tool that simplifies generating the code
required for programs to accept options. I [15]talked about gengetopt a
while back on this blog.
The discussion surrounds support for internationalization, which simply
means a program printing output in whatever language your system is
using. A very popular means to accomplish this is the GNU gettext
library, or its counterpart in various other operating systems.
Disclamer, if you do not care about C standards and common UNIX
programming, this post will probably bore you to tears. However, your
welcome to read on if only to discover how much I value life in boring
geeky flavors :)
Recently, while working on HelenOS I found the need to implement
getopt. I'm working on something a lot like busybox, but from scratch.
Rather than re-invent the getopt wheel yet again, I dove into the
source code of GNU getopt as well as the various *BSD implementations
to find the one that was easiest to port. One thing that stood out at
me was that most implementations declared error strings and formats as
static, English strings.
A week later, a proposal to add gettext support came across the
gengetopt mailing list. I voted to not include it because the resulting
output would be at best mixed, as error strings in basic C89/C99 libc
are hard coded, usually in English. The getopt family of functions are
an interesting corner case, most core libc functions never print
anything ... they just exit with some value and set a global errno to
inform the calling function of what went wrong. Its then up to the
calling function to (use or not use) something like gettext to display
the information in the appropriate language.
This got me thinking .. if we're making a truly modern operating system
based on C89/C99 .. internationalization must be easy to leverage.
Talking with Lorenzo, some interesting ideas came to light.
Gettext is a great tool, however it introduces dependencies on shared
objects (or requires static linking). Simply parsing command line
arguments should not introduce additional dependencies. Additionally,
standard libc should not favor one internationalization library over
another, therefore its just not practical to include
internationalization in standard libc. However, stuff in libc that
prints strings can remain friendly to internationalization by simply
requiring one tiny additional step - have the programmer register a
callback function that gets all output instead of printing to the error
file descriptor directly in libc.
For instance, a modern getopt might look like this:
void getopt_callback(int level, char *format, int line)
{
switch (level) {
case GETOPT_EOK:
fprintf(stdout, "line %d of getopt.c says %s", line, format);
break;
case GETOPT_EFAIL:
fprintf(stderr, "line %d of getopt.c says %s", line, format);
break;
}
return;
}
int main(int argc, char **argv)
{
int c, opt_ind;
getopt_register_callback(getopt_callback);
for (c = 0, optind = 0, opt_ind = 0; c != -1;) {
c = getopt_long(argc, argv, "f:o:O", long_options, &opt_ind);
......
As we can see, the getopt implementation does not actually print
anything, it allows the callback function to handle that. One could
very easily use internationalization tools within the callback, if they
wanted to do so. This goes (basically) for anything in core libc that
prints anything. The callback may be better typed as something like
getopt_callback_t.
This seems to be the favorable approach. Of course, getopt would
feature its own static callback that printed the strings as-is if the
calling function did not register one, this keeps from breaking
existing use.
After I finish some other tasks, I am going to take a stroll through
the HelenOS userspace generic libc to see if getopt is the only case
where this should be implemented. At the least, I'll implement this
getopt method there so that programs can be fully internationalized.
This also shows the virtue of not using printf() directly when you can
avoid it. Writing your own functions to print warnings or messages
allows someone else (even you) to go back and make only a few minor
changes in order for your program to support any language.
Working on a new OS that aims to be fully modern presents interesting
opportunities to pick things apart. Hopefully, this didn't put you to
sleep :)
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