Variable arg function question
Hi all I need to implement a variable argument function in C. The number of args are not known but the type is known, all are strings. Unfortunately va_arg() [stdarg(3)] does not return NULL or any other suitable value after processing the arg list, it just simply crashes once the arg list is exhausted. It seems there is no way to know the number of args inside the called function. How do you guys implement variable arg function such as f(str1, str2, str3, ..., strN)? Sorry for the sightly off topic question, the only relevance is I'm programming this app on FreeBSD 7.0 :) Many thanks in advance. Kind regards Unga Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Variable arg function question
On Sun, May 04, 2008 at 12:40:43AM -0700, Unga wrote: Hi all I need to implement a variable argument function in C. The number of args are not known but the type is known, all are strings. Unfortunately va_arg() [stdarg(3)] does not return NULL or any other suitable value after processing the arg list, it just simply crashes once the arg list is exhausted. It is _your_ task to properly close the argument list. E.g. by supplying a NULL pointer as the last argument. It seems there is no way to know the number of args inside the called function. Not with stdarg. How do you guys implement variable arg function such as f(str1, str2, str3, ..., strN)? you could use the same format as main: int foo(int num, char **args) Roland -- R.F.Smith http://www.xs4all.nl/~rsmith/ [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725) pgp8rpDPLi4A8.pgp Description: PGP signature
Re: Variable arg function question
--- Roland Smith [EMAIL PROTECTED] wrote: On Sun, May 04, 2008 at 12:40:43AM -0700, Unga wrote: Hi all I need to implement a variable argument function in C. The number of args are not known but the type is known, all are strings. Unfortunately va_arg() [stdarg(3)] does not return NULL or any other suitable value after processing the arg list, it just simply crashes once the arg list is exhausted. It is _your_ task to properly close the argument list. E.g. by supplying a NULL pointer as the last argument. Infact, I have implemented it in this way. I was wondering if there is a better way. The issue I see is, if someone forget to close the arg list with NULL pointer, it crashes. How do you guys implement variable arg function such as f(str1, str2, str3, ..., strN)? you could use the same format as main: int foo(int num, char **args) This is interesting. Who set the num? The compiler or the user. If it is the user, its no better than above NULL pointer method. If this is possible, my problem is solved: f(str1, str2, str3, ..., strN) is at compile time expands to _f(int num, str1, str2, str3, ..., strN). The num is set automatically by the compiler by counting the args. Is this possible? Unga Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Variable arg function question
On Sun, May 04, 2008 at 04:01:39AM -0700, Unga wrote: Unfortunately va_arg() [stdarg(3)] does not return NULL or any other suitable value after processing the arg list, it just simply crashes once the arg list is exhausted. It is _your_ task to properly close the argument list. E.g. by supplying a NULL pointer as the last argument. Infact, I have implemented it in this way. I was wondering if there is a better way. Not really within the bounds of the C language. How do you guys implement variable arg function such as f(str1, str2, str3, ..., strN)? you could use the same format as main: int foo(int num, char **args) This is interesting. Who set the num? The compiler or the user. If it is the user, its no better than above NULL pointer method. If this is possible, my problem is solved: f(str1, str2, str3, ..., strN) is at compile time expands to _f(int num, str1, str2, str3, ..., strN). The num is set automatically by the compiler by counting the args. Is this possible? You could write a custom preporcessor that translates f calls into calls for _f. Roland -- R.F.Smith http://www.xs4all.nl/~rsmith/ [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725) pgpSHdHk0d8UA.pgp Description: PGP signature
Re: Variable arg function question
Unga wrote: Hi all I need to implement a variable argument function in C. The number of args are not known but the type is known, all are strings. Unfortunately va_arg() [stdarg(3)] does not return NULL or any other suitable value after processing the arg list, it just simply crashes once the arg list is exhausted. It seems there is no way to know the number of args inside the called function. Why is it in your opinion so hard to count the number of arguments *before* you call the function, in other words, what in your program prevents this count? Peter -- http://www.boosten.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Variable arg function question
What about using a macro (...) in front of the function to csll it which passes __VARARGS__, NULL to ensure there is always a trailing NULL? I think this would at least work in GCC... Can' test on my phone though. -Patrick On May 4, 2008, at 4:42 AM, Peter Boosten [EMAIL PROTECTED] wrote: Unga wrote: Hi all I need to implement a variable argument function in C. The number of args are not known but the type is known, all are strings. Unfortunately va_arg() [stdarg(3)] does not return NULL or any other suitable value after processing the arg list, it just simply crashes once the arg list is exhausted. It seems there is no way to know the number of args inside the called function. Why is it in your opinion so hard to count the number of arguments *before* you call the function, in other words, what in your program prevents this count? Peter -- http://www.boosten.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Variable arg function question
On Sun, May 04, 2008 at 07:02:36AM -0700, Patrick Clochesy wrote: What about using a macro (...) in front of the function to csll it which passes __VARARGS__, NULL to ensure there is always a trailing NULL? I think this would at least work in GCC... Can' test on my phone though. That's a good idea. If one uses __VA_ARGS__ instead of __VARARGS__, it should work with any C99 compliant compiler, including gcc. The good thing about variadic macros in C99[1] is that you don't need a first argument. Roland [1: http://en.wikipedia.org/wiki/Variadic_macro] -- R.F.Smith http://www.xs4all.nl/~rsmith/ [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725) pgpJYoWnrc9Ch.pgp Description: PGP signature
Re: Variable arg function question
--- Roland Smith [EMAIL PROTECTED] wrote: On Sun, May 04, 2008 at 07:02:36AM -0700, Patrick Clochesy wrote: What about using a macro (...) in front of the function to csll it which passes __VARARGS__, NULL to ensure there is always a trailing NULL? I think this would at least work in GCC... Can' test on my phone though. That's a good idea. If one uses __VA_ARGS__ instead of __VARARGS__, it should work with any C99 compliant compiler, including gcc. The good thing about variadic macros in C99[1] is that you don't need a first argument. Roland [1: http://en.wikipedia.org/wiki/Variadic_macro] -- I gave it a try, but I cannot get it to work: (As per above wikipedia example) void realdprintf (char const *file, int line, char const *fmt, ...); #define dprintf(...) realdprintf(__FILE__, __LINE__, __VA_ARGS__) To solve my problem, I must be able to indicate the end of the arg list, may be by a empty string (), but GNU C compiler does not allow to specify anything after the ... . How do I specify end of arg list? or is that the way? Unga Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Variable arg function question
On Sun, May 04, 2008 at 08:34:30AM -0700, Unga wrote: --- Roland Smith [EMAIL PROTECTED] wrote: On Sun, May 04, 2008 at 07:02:36AM -0700, Patrick Clochesy wrote: What about using a macro (...) in front of the function to csll it which passes __VARARGS__, NULL to ensure there is always a trailing NULL? I think this would at least work in GCC... Can' test on my phone though. That's a good idea. If one uses __VA_ARGS__ instead of __VARARGS__, it should work with any C99 compliant compiler, including gcc. I gave it a try, but I cannot get it to work: (As per above wikipedia example) void realdprintf (char const *file, int line, char const *fmt, ...); #define dprintf(...) realdprintf(__FILE__, __LINE__, __VA_ARGS__) To solve my problem, I must be able to indicate the end of the arg list, may be by a empty string (), but GNU C compiler does not allow to specify anything after the ... . Try something like what Patrick suggested: #define f(...) _f(__VA_ARGS__,NULL) Roland -- R.F.Smith http://www.xs4all.nl/~rsmith/ [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725) pgp9mvXJN9jch.pgp Description: PGP signature
Re: Variable arg function question [SOLVED]
--- Roland Smith [EMAIL PROTECTED] wrote: On Sun, May 04, 2008 at 08:34:30AM -0700, Unga wrote: --- Roland Smith [EMAIL PROTECTED] wrote: On Sun, May 04, 2008 at 07:02:36AM -0700, Patrick Clochesy wrote: What about using a macro (...) in front of the function to csll it which passes __VARARGS__, NULL to ensure there is always a trailing NULL? I think this would at least work in GCC... Can' test on my phone though. That's a good idea. If one uses __VA_ARGS__ instead of __VARARGS__, it should work with any C99 compliant compiler, including gcc. I gave it a try, but I cannot get it to work: (As per above wikipedia example) void realdprintf (char const *file, int line, char const *fmt, ...); #define dprintf(...) realdprintf(__FILE__, __LINE__, __VA_ARGS__) To solve my problem, I must be able to indicate the end of the arg list, may be by a empty string (), but GNU C compiler does not allow to specify anything after the ... . Try something like what Patrick suggested: #define f(...) _f(__VA_ARGS__,NULL) Hey, it worked :) Thanks guys for the help. Appreciate it very much. Unga Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
