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Prototyping rules/recommendations sought

 
 
rs
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      11-28-2003
Dear All,


I have a question regarding proptypes for functions. What is the
recommended practice? The way I do it is to put all my external functions
in a header file, while protyping internal (file scope) functions at the
start of the source file. I've seen many people (especially using gcc
under linux) don't botehr prototyping internal functions but just declare
them inline so to speak.

Is there any recommendations advantages/disdvantages of the approach? It
seems to be that there is a tradeoff here:

1. If the prototypes are going to help me by catching incorrect parameter
types,numbers etc.. they are worth having

2. However its a hassle to maintain them.

So, the question is, are most modern compilers able to catch type/number
errors so that I can avoid prototyping internal functions? What are your
suggestions?

 
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Hallvard B Furuseth
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      11-28-2003
rs wrote:

> So, the question is, are most modern compilers able to catch type/number
> errors so that I can avoid prototyping internal functions? What are your
> suggestions?


If a function has no declaration, only a definition, and is used before
it is defined, it gets used without a prototype. Some compilers may
give a warning if the expected prototype is wrong, but they may not
infer the prototype from the later definition. So you should prototype
such static functions. Other static functions need no declarations.

Of course, you might forget that you are using a static function before
declaring it unless the compiler warns about implicitly declared
functions (e.g. with the gcc -Wimplicit option), so you may prefer to
declare all static functions anyway.

--
Hallvard
 
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Robert Stankowic
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      11-28-2003

"rs" <(E-Mail Removed)> schrieb im Newsbeitrag
news:bq7mi7$lri$(E-Mail Removed)...
> Dear All,
>
>
> I have a question regarding proptypes for functions. What is the
> recommended practice? The way I do it is to put all my external functions
> in a header file, while protyping internal (file scope) functions at the
> start of the source file. I've seen many people (especially using gcc
> under linux) don't botehr prototyping internal functions but just declare
> them inline so to speak.
>
> Is there any recommendations advantages/disdvantages of the approach? It
> seems to be that there is a tradeoff here:
>
> 1. If the prototypes are going to help me by catching incorrect parameter
> types,numbers etc.. they are worth having
>
> 2. However its a hassle to maintain them.
>
> So, the question is, are most modern compilers able to catch type/number
> errors so that I can avoid prototyping internal functions? What are your
> suggestions?


Not a suggestion (who am I to give suggestions)..
I write the functions in a compilation unit "upside down" and put protoypes
of only those functions which are called from a different compilation unit
into a header:

in somecode.c:

int foo(void)
{
return 1;
}

double bar(double some_val)
{
return some_val / 1.234;
}

int main(void)
{
int int_val = foo();
double my_dbl = bar(2.55);
return 0;
}

in somecode.h i have only

double bar(double);
because foo() is used only in somecode.c, but bar() is called from
someothercode.c as well.

just my <whatever currency you like> 0.02
Robert


 
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Irrwahn Grausewitz
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Posts: n/a
 
      11-28-2003
"Robert Stankowic" <(E-Mail Removed)> wrote:

> "rs" <(E-Mail Removed)> schrieb:

<snip>
> > So, the question is, are most modern compilers able to catch type/number
> > errors so that I can avoid prototyping internal functions? What are your
> > suggestions?

>
> Not a suggestion (who am I to give suggestions)..
> I write the functions in a compilation unit "upside down" and put protoypes
> of only those functions which are called from a different compilation unit
> into a header:
>
> in somecode.c:
>
> int foo(void)
> {
> return 1;
> }


You may want to change this to:

static int foo(void)
...

<snip>
> just my <whatever currency you like> 0.02


I added mine, that makes 0.04.

Regards
--
Irrwahn
((E-Mail Removed))
 
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Mark F. Haigh
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Posts: n/a
 
      11-29-2003
rs wrote:

> Dear All,
>

<snip>
>
> 1. If the prototypes are going to help me by catching incorrect parameter
> types,numbers etc.. they are worth having

<snip>
> So, the question is, are most modern compilers able to catch type/number
> errors so that I can avoid prototyping internal functions? What are your
> suggestions?
>


Quoting the C90 & C99 standards: A function prototype is a declaration
of a function that declares the types of its parameters.

We end up with the interesting effect that the definition of a function
is also a prototype:

/* Both definition and prototype! */
static int foo(char *p)
{
/* ... */
return 42;
}

int main(void)
{
char *p;
foo(p); /* Prototype in scope, full type checking */
return 0;
}

Many experienced programmers do this whenever possible for static
functions. As you noted, why maintain function prototypes for static
functions when you don't have to?


Mark F. Haigh
http://www.velocityreviews.com/forums/(E-Mail Removed)


 
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Robert Stankowic
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      11-29-2003

"Irrwahn Grausewitz" <(E-Mail Removed)> schrieb im Newsbeitrag
news:(E-Mail Removed)...
> "Robert Stankowic" <(E-Mail Removed)> wrote:
>
> > "rs" <(E-Mail Removed)> schrieb:

> <snip>
> > > So, the question is, are most modern compilers able to catch

type/number
> > > errors so that I can avoid prototyping internal functions? What are

your
> > > suggestions?

> >
> > Not a suggestion (who am I to give suggestions)..
> > I write the functions in a compilation unit "upside down" and put

protoypes
> > of only those functions which are called from a different compilation

unit
> > into a header:
> >
> > in somecode.c:
> >
> > int foo(void)
> > {
> > return 1;
> > }

>
> You may want to change this to:
>
> static int foo(void)
> ...


Yes, thank you.

>
> <snip>
> > just my <whatever currency you like> 0.02

>
> I added mine, that makes 0.04.


100% in less than one day.. not so bad, really

Regards
Robert


 
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rs
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Posts: n/a
 
      11-29-2003
Does this apply only to functions that are defined BEFORE they are used or
also to those defined after they are used?


"Mark F. Haigh" <(E-Mail Removed)> wrote in message
news:r7Xxb.61676$(E-Mail Removed). com...
> rs wrote:
>
> > Dear All,
> >

> <snip>
> >
> > 1. If the prototypes are going to help me by catching incorrect

parameter
> > types,numbers etc.. they are worth having

> <snip>
> > So, the question is, are most modern compilers able to catch type/number
> > errors so that I can avoid prototyping internal functions? What are

your
> > suggestions?
> >

>
> Quoting the C90 & C99 standards: A function prototype is a declaration
> of a function that declares the types of its parameters.
>
> We end up with the interesting effect that the definition of a function
> is also a prototype:
>
> /* Both definition and prototype! */
> static int foo(char *p)
> {
> /* ... */
> return 42;
> }
>
> int main(void)
> {
> char *p;
> foo(p); /* Prototype in scope, full type checking */
> return 0;
> }
>
> Many experienced programmers do this whenever possible for static
> functions. As you noted, why maintain function prototypes for static
> functions when you don't have to?
>
>
> Mark F. Haigh
> (E-Mail Removed)
>
>



 
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CBFalconer
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Posts: n/a
 
      11-29-2003
Robert Stankowic wrote:
> "rs" <(E-Mail Removed)> schrieb im Newsbeitrag
> >
> > I have a question regarding proptypes for functions. What is the
> > recommended practice? The way I do it is to put all my external
> > functions in a header file, while protyping internal (file scope)
> > functions at the start of the source file. I've seen many people
> > (especially using gcc under linux) don't botehr prototyping
> > internal functions but just declare them inline so to speak.
> >
> > Is there any recommendations advantages/disdvantages of the
> > approach? It seems to be that there is a tradeoff here:
> >
> > 1. If the prototypes are going to help me by catching incorrect
> > parameter types,numbers etc.. they are worth having
> >
> > 2. However its a hassle to maintain them.
> >
> > So, the question is, are most modern compilers able to catch
> > type/number errors so that I can avoid prototyping internal
> > functions? What are your suggestions?

>
> Not a suggestion (who am I to give suggestions)..
> I write the functions in a compilation unit "upside down" and put
> protoypes of only those functions which are called from a different
> compilation unit into a header:
>
> in somecode.c:
>
> int foo(void)
> {
> return 1;
> }
>
> double bar(double some_val)
> {
> return some_val / 1.234;
> }
>
> int main(void)
> {
> int int_val = foo();
> double my_dbl = bar(2.55);
> return 0;
> }
>
> in somecode.h i have only
>
> double bar(double);
> because foo() is used only in somecode.c, but bar() is called from
> someothercode.c as well.


In this case you should also declare foo() as being static, to
avoid polluting the external name space. The general rule is that
the header contains only things meant to be visible to other
modules. Because of the context sensitive meaning of static, you
should use it for all declarations visible over file scope that
are NOT intended to be visible externally.

--
Chuck F ((E-Mail Removed)) ((E-Mail Removed))
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!


 
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Irrwahn Grausewitz
Guest
Posts: n/a
 
      11-29-2003
"rs" <(E-Mail Removed)> wrote:

[Please don't top-post; fixed.]

> "Mark F. Haigh" <(E-Mail Removed)> wrote:

<snip>
> > Quoting the C90 & C99 standards: A function prototype is a declaration
> > of a function that declares the types of its parameters.
> >
> > We end up with the interesting effect that the definition of a function
> > is also a prototype:
> >
> > /* Both definition and prototype! */
> > static int foo(char *p)
> > {
> > /* ... */
> > return 42;
> > }
> >
> > int main(void)
> > {
> > char *p;
> > foo(p); /* Prototype in scope, full type checking */
> > return 0;
> > }
> >
> > Many experienced programmers do this whenever possible for static
> > functions. As you noted, why maintain function prototypes for static
> > functions when you don't have to?

>
> Does this apply only to functions that are defined BEFORE they are used or
> also to those defined after they are used?


To have a prototype in scope when a function is called, the function
has to be either defined (as a function definition serves as prototype
as well) or explicitly prototyped /before/ used.

Mark's example above is of the first kind: definition before use.

The same example, using a separate prototype:

/* Prototype: */
static int foo(char *);

int main(void)
{
char *p;
foo(p); /* Prototype in scope, full type checking */
return 0;
}

/* Note that the definition of foo can now savely be
moved to the end of the file: */

static int foo(char *p)
{
/* ... */
return 42;
}

If you omit the prototype in this example, the compiler cannot
perform full type checking.

HTH
Regards
--
Irrwahn
((E-Mail Removed))
 
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Mark Gordon
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Posts: n/a
 
      11-30-2003
On Sat, 29 Nov 2003 18:31:15 +0100
Irrwahn Grausewitz <(E-Mail Removed)> wrote:

> "rs" <(E-Mail Removed)> wrote:
>
> [Please don't top-post; fixed.]
>
> > "Mark F. Haigh" <(E-Mail Removed)> wrote:

> <snip>
> > > Quoting the C90 & C99 standards: A function prototype is a
> > > declaration of a function that declares the types of its
> > > parameters.
> > >
> > > We end up with the interesting effect that the definition of a
> > > function is also a prototype:
> > >
> > > /* Both definition and prototype! */
> > > static int foo(char *p)
> > > {
> > > /* ... */
> > > return 42;
> > > }
> > >
> > > int main(void)
> > > {
> > > char *p;
> > > foo(p); /* Prototype in scope, full type checking */
> > > return 0;
> > > }
> > >
> > > Many experienced programmers do this whenever possible for static
> > > functions. As you noted, why maintain function prototypes for
> > > static functions when you don't have to?

> >
> > Does this apply only to functions that are defined BEFORE they are
> > used or also to those defined after they are used?

>
> To have a prototype in scope when a function is called, the function
> has to be either defined (as a function definition serves as prototype
> as well) or explicitly prototyped /before/ used.


<snip>

<mode=awkward sod>
Not all function definitions provide prototypes.
static int foo(*p)
char *p
{
/* ... */
return 42;
}

does not provide a prototype. This, of course, is a very good reason for
never using this type of function definition.
</mode>
--
Mark Gordon
Paid to be a Geek & a Senior Software Developer
Although my email address says spamtrap, it is real and I read it.
 
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