*/ Use prototypes unless the compiler is old-fashioned. /*
#if __STDC__
#define P(x) x
#else
#define P(x) ()
#endif
/* Prototype function declaration. */
int isroot P((uid_t));
/* Old-style function definition. */
int isroot (x) /* ??? lossage here ??? */
uid_t x;
{
return x == 0;
}
Suppose the type, uid_t,
happens to be short.
ANSI C does not allow this example, because subword arguments in old-style
non-prototype definitions are promoted. Therefore in this example the function
definition’s argument is really an int,
which does not match the prototype argument type of short.
This restriction of ANSI C makes it hard to write code that is portable to traditional C compilers, because the programmer does not know whether the uid_t type is short, int, or long.
Therefore, in cases like these GNU C allows a prototype to override a later old-style definition. More precisely, in GNU C, a function prototype argument type overrides the argument type specified by a later old-style definition if the former type is the same as the latter type before promotion. Thus, in GNU C, the previous example is equivalent to the following:
int isroot (uid_t);
int
isroot (uid_t x)
{
return x == 0;
}
GNU C++ does not support old-style
function definitions, so the previous example’s extension is irrelevant.