differently or not?

[quantt]

hello,
tell me please, if two different ways to using struct or not?
funclion called in head source file like this...

static void func(struct a *);

next I need use it.
which's way would be most good?

//1
 func(struct a *p){
..
}
//2
 func(p)
 struct  a *p;
{
..
}

[laserlight]

It looks like you are talking about parameter declaration style, and consequently the former is better because it is more commonly used nowadays, and ensures that the parameter type is made known.

[itCbitC]

The second one is old, pre-ANSI style declarations.

[P4R4N01D]

Even better to call like this with the return type specified, so it is clear which type the function returns w/o consulting the prototype:

void func(struct a *p) { ... }

//2
func(p)
struct a *p;
{

This at first looks as if p is being redeclared (which it would be if struct a *p was after the {).

The second one is old, pre-ANSI style declarations.

I never knew that this was ever a valid declaration.

[laserlight]

I never knew that this was ever a valid declaration.

It is still valid, though I do not think it has been deprecated/obsoleted despite being practically obsolete.

[itCbitC]

I never knew that this was ever a valid declaration.

AFAIK that syntax is supported only by legacy compilers not the modern ones. Some modern ones have options that morph them into legacy compilers but those are few and far between.

[P4R4N01D]

Ah, thanks. Still should avoid using it where possible though -> Maximise portibility

[laserlight]

AFAIK that syntax is supported only by legacy compilers not the modern ones.

I do not think so, since that syntax remains part of even the 1999 edition of the C standard.

EDIT:
Ah, but I have found where the standard does say that the feature is obsolescent - section 6.1.1.7 of C99: "The use of function definitions with separate parameter identifier and declaration lists (not prototype-format parameter type and identifier declarators) is an obsolescent feature." However, an obsolescent feature is one that has been considered for withdrawal in future versions of the standard.