Обсуждение: stringify MAKE_SQLSTATE()

Hi!

Following discussion at https://commitfest.postgresql.org/5/190/ patch, I found 
(at seems to me) a way to stringify MAKE_SQLSTATE(), the idea is to use char 
array as string:

#include <stdio.h>

#define MAKE_SQLSTATE(ch1,ch2,ch3,ch4,ch5) \
((char[]){(char)(ch1),(char)(ch2),(char)(ch3),(char)(ch4),(char)(ch5),(char)'\0'})

#define ERRCODE_WARNING_DEPRECATED_FEATURE MAKE_SQLSTATE('0','1','P','0','1')

int
main(int argn, char* argv[])
{    char    *x = ERRCODE_WARNING_DEPRECATED_FEATURE;
    printf("%s\n", x);
    return 0;
}

That works for clang ang gcc48 with flags -Wall -Wextra -ansi (or -std=c90) 
without warnings, but doesn't work with -pedantic. Is that enough to to work 
with other compilers?

-- 
Teodor Sigaev                                   E-mail: teodor@sigaev.ru
  WWW: http://www.sigaev.ru/
 

Teodor Sigaev <teodor@sigaev.ru> writes:
> Following discussion at https://commitfest.postgresql.org/5/190/ patch, I found 
> (at seems to me) a way to stringify MAKE_SQLSTATE(), the idea is to use char 
> array as string:

> #define MAKE_SQLSTATE(ch1,ch2,ch3,ch4,ch5) \
> ((char[]){(char)(ch1),(char)(ch2),(char)(ch3),(char)(ch4),(char)(ch5),(char)'\0'})

I'm pretty sure that's a gcc-ism, not standard C.

As I mentioned in the other thread, if we wanted to provide string
versions of the ERRCODE macros, the safest way to do it would be
to create a separate header file with defines like

#define ERRCODE_WARNING_DEPRECATED_FEATURE "01P01"

Now that we generate errcodes.h from errcodes.txt anyway, it would
certainly be a trivial extension of the build infrastructure to make
a second header like this.

The real question is do we want to.  What's your use-case for this?
        regards, tom lane

>> #define MAKE_SQLSTATE(ch1,ch2,ch3,ch4,ch5) \
>> ((char[]){(char)(ch1),(char)(ch2),(char)(ch3),(char)(ch4),(char)(ch5),(char)'\0'})
>
> I'm pretty sure that's a gcc-ism, not standard C.
Hmm, after some digging: the feature is called compound literals and it was 
introduced in c99 although gcc has support in c90. To disable this support it's 
needed a flag -pedantic. Sorry.

> The real question is do we want to.  What's your use-case for this?
Just do not have a hardcoded values. It is too easy to make a mistake in 
hardcoded value.




-- 
Teodor Sigaev                                   E-mail: teodor@sigaev.ru
  WWW: http://www.sigaev.ru/