Re: head.c usage function
On Fri, May 26, 2006 at 08:47:15PM +0100, Nick Guenther wrote: least, it should be) in usage() because the proper form is fprintf(stderr, usage: %s [-ks]\n, __progname); where __progname gets filled in automatically with the name of the program. I don't know the details of how it works though, does anyone have a link to an explanation? I'm not sure about this, but isn't __progname a compiler-specific extension? I usually write a usage function to take a single argument, i.e. usage(const char *progname). When I call usage(), which is always from main(), I just pass in argv[0]. I'm under the impression that argv[0] being set to the name of the program is standard (could be wrong though). MG
Re: head.c usage function
Be careful -- if you have an application say /usr/local/whatever/foo that is linked from /usr/local/bin/bar then when you call /usr/local/bin/bar it will populate bar as the argv[0] element. This may be what you want, but then again, perhaps you want to know that foo is the application being called. __progname *should* ensure that foo is is being used when doing things like opening app-name specific logs etc. On 5/30/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: I usually write a usage function to take a single argument, i.e. usage(const char *progname). When I call usage(), which is always from main(), I just pass in argv[0]. I'm under the impression that argv[0] being set to the name of the program is standard (could be wrong though).
Re: head.c usage function
Gak! The should was hedged with quotes because I couldn't verify how it behaved. Apparently it's just a quick way to access argv[0]. Thanks! On 30 May 2006 16:29:31 +0200, Artur Grabowski [EMAIL PROTECTED] wrote: Peter Blair [EMAIL PROTECTED] writes: Be careful -- if you have an application say /usr/local/whatever/foo that is linked from /usr/local/bin/bar then when you call /usr/local/bin/bar it will populate bar as the argv[0] element. This may be what you want, but then again, perhaps you want to know that foo is the application being called. __progname *should* ensure that foo is is being used when doing things like opening app-name specific logs etc. should? Says who? How do you handle hard links then? Why should anyone even care what the file name was? The kernel isn't even aware that a symbolic link was followed when performing the exec system call (it could be made aware of the fact by horrible layering violations in the filesystem code and/or best effort measures that would break down in case of hard links). $ grep usage: /usr/src/bin/rm/rm.c (void)fprintf(stderr, usage: %s [-dfiPRr] file ...\n, __progname); $ rm -J rm: unknown option -- J usage: rm [-dfiPRr] file ... $ ln -s /bin/rm /tmp/foo $ /tmp/foo -J foo: unknown option -- J usage: foo [-dfiPRr] file ... $ See: /usr/src/lib/csu/*/crt0.c that fills in __progname. Considering that argv[0] can be set to anything by the caller, __progname can be set to anything too. If you trust it, you're wrong. //art On 5/30/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: I usually write a usage function to take a single argument, i.e. usage(const char *progname). When I call usage(), which is always from main(), I just pass in argv[0]. I'm under the impression that argv[0] being set to the name of the program is standard (could be wrong though).
head.c usage function
On 5/30/06, Peter Blair [EMAIL PROTECTED] wrote: Be careful -- if you have an application say /usr/local/whatever/foo that is linked from /usr/local/bin/bar then when you call /usr/local/bin/bar it will populate bar as the argv[0] element. Wrong, argv[0] will be whatever was passed to execvp as the first element of the second argument. (If that is not clear remember that the second argument is a NULL-terminated array of char pointers.) Although in most cases it will be set to the name of the application or a path to it. This may be what you want, but then again, perhaps you want to know that foo is the application being called. __progname *should* ensure that foo is is being used when doing things like opening app-name specific logs etc. Wrong again, __progname is derived from argv[0]. That's what enable things like crunchgen to work by altering the function of the program based on its name. On 5/30/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: I usually write a usage function to take a single argument, i.e. usage(const char *progname). When I call usage(), which is always from main(), I just pass in argv[0]. I'm under the impression that argv[0] being set to the name of the program is standard (could be wrong though). __progname is filled in at program initialisation time (in ___start) with everything after the last / in argv[0]. It has nothing to do with the compiler. If you don't trust me, trust the sources: http://www.openbsd.org/cgi-bin/cvsweb/src/lib/csu/i386/crt0.c?rev=1.13content-type=text/x-cvsweb-markup -- i think we should rewrite the kernel in java since it has good support for threads. - Ted Unangst
head.c usage function
Looking at /bin/head source code. The usage function uses: fputs(usage: head [-n line_count] [file ...]\n, stderr); While many other programs use: fprintf(stderr, usage: arch [-ks]\n); Is there a difference? Is one preferred? Yes, I know. I should take a C programming course.
Re: head.c usage function
On 5/26/06, Will H. Backman [EMAIL PROTECTED] wrote: Looking at /bin/head source code. The usage function uses: fputs(usage: head [-n line_count] [file ...]\n, stderr); While many other programs use: fprintf(stderr, usage: arch [-ks]\n); Is there a difference? Is one preferred? Yes, I know. I should take a C programming course. all the printf functions are formatted printing. If you aren't formatting then there is no difference. fprintf is more often used (at least, it should be) in usage() because the proper form is fprintf(stderr, usage: %s [-ks]\n, __progname); where __progname gets filled in automatically with the name of the program. I don't know the details of how it works though, does anyone have a link to an explanation? -Nick
