Re: A question about an include file.

["Jens B. Jorgensen" <jjorgens@bdsinc.com>]

__P is basically a macro that lets the declaration work with both K&R-style and ANSI C
compilers. I haven't looked at it directly but it's something like

#if (K_AND_R)
#define __P(x) x
#elif (ANSI_C)
#define __P(x)
#endif

__const is likewise a macro, probably to work with compilers which don't like const.

There are info pages for the C Preprocessor if you're intested in syntax. I doubt
there's any documentation per se for these conventions used by the C library headers.

shaul@rakefet.debian.org.bdsinc.com wrote:

> Could someone explain what the following line, which is taken from
> /usr/include/errno.h, means :
>
>         extern void     perror __P ((__const char* __s));
>
> As I understand it, it means that perror is defined in an external file and
> returns a void type. But what are the __P, and __const ? And why there are 2
> sets of brackets, and not only 1 ?
> Where does these constructs being documented ?

--
Jens B. Jorgensen
jjorgens@bdsinc.com



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