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

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

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?

>
> gcc provides cctype which follows various C++ standards.
> -mike

Again forgive me that I really know little about glibc, but I cannot find so
many docs about it by Googling.


-- 
Regards,
Hongxu Chen