Re: Declaration of isspace in C/C++ not consistent?

[Hongxu Chen <leftcopy dot chx at gmail dot com>]

OndÅej BÃlka <neleai@seznam.cz> writes:

> On Sun, Jun 02, 2013 at 11:42:11PM +0800, Hongxu Chen wrote:
>> Mike Frysinger <vapier@gentoo.org> writes:
>> 
>> > On Sunday 02 June 2013 10:45:21 Hongxu Chen wrote:
>> >> Hi list,
>> >> 
>> >> Maybe this question is a bit silly, but I just cannot understand why
>> >> `isspace` seems not consistent for C and C++(I have put this question in
>> >> stackoverflow but no satisfactory answer has been given yet).
>> >> 
>> >> I am using *clang* analyzer to get the definition information and I know
>> >> quite little about the mechanism behind it, so the declaration result
>> >> might not be accurate; but I am just confused.
>> >> 
>> >> For c code like this:
>> >> 
>> >>     // test.c
>> >>     #include <ctype.h>
>> >>     int main(int argc, char *argv[]) {
>> >>       isspace('a');
>> >>       return 0;
>> >>     }
>> >> 
>> >> clang reports below as the declaration of isspace:
>> >> 
>> >>     # define isspace(c)	__isctype((c), _ISspace)  // LINE 207 in
>> >> /usr/include/ctype.h
>> >> 
>> >> and when for this snippet:
>> >> 
>> >>     // test.cpp
>> >>     #include <cctype>
>> >>     int main() {
>> >>       std::isspace('t');
>> >>       return 0;
>> >>     }
>> >> 
>> >> clang reports the declaration here:
>> >> 
>> >>     __exctype (isspace);  // LINE 120 in /usr/include/ctype.h
>> >>     // #define	__exctype(name)	extern int name (int) __THROW
>> >> 
>> >> So why should there be such a difference?
>> >
>> > glibc provides ctype.h which follows POSIX:
>> > http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/ctype.h.html
>> > we provide both real funcs and macros for each because the standard allows it, 
>> > and the macro ends up producing better code at runtime.
>> 
>> You mean that the c code is a macro implementation and it generates
>> better runtime binary while C++ code uses the function one? By saying
>> macro you mean `__ctype_b_loc'?(Actually I don't know what this symbol
>> does)
>> 
>> # define __isctype(c, type) \
>>   ((*__ctype_b_loc ())[(int) (c)] & (unsigned short int) type)
>> 
>> Also there is another implementation called `__isctype_f', which is
>> defined as:
>> 
>> # define __isctype_f(type) \
>>   __extern_inline int							      \
>>   is##type (int __c) __THROW						      \
>>   {									      \
>>     return (*__ctype_b_loc ())[(int) (__c)] & (unsigned short int) _IS##type; \
>>   }
>> 
>> Then what's this supposed to be doing?
>> 
> Replace function call by simple table lookup where table is 1 for character
> inside class and 0 otherwise.

Would you please tell some more details? You mean __isctype_f
implementation would actually lookup a _ISspacetype table and find
whether `c' is 1 in the table? Or you are talking about __isctype?

-- 
Regards,
Hongxu Chen