How to prototype functions that return pointers

How to prototype functions that return pointers

[James Colannino]

Ok, so this is a very embarassing question.  I tried googling for the
answer but haven't figured it out yet, and everything I've tried results
in compilation errors. I want to prototype a function that takes nothing
as an argument but returns a pointer to a character.

I've tried the following:

char * readline();
char *readline();

These first two result in 4 errors, each one identical and each one
telling me "error: two or more data types in declaration of 'readline' "

*char readline();
* char readline();

These second two result in "error: syntax error before 'char' "

I know this should be so simple, but I can't for the life of me figure
this out.  Thanks very much in advance.

James
-- 
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My homepage: http://james.colannino.org/

" Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety." --Benjamin Franklin

Re: How to prototype functions that return pointers

[James Colannino]

Richard Nairn wrote:
> Believe the correct decleration is (char *) readline();
> 
> Order of ops.

That was the next one I tried.  That yielded a syntax error.  I found
out though that the "two or more data types" error was the result of a
more difficult bug to find that had to do with something in another
header file.  Once I fixed that, the declaration char * readline();
worked.  Needless to say I'm very embarassed now... :-P

James
-- 
My blog: http://www.crazydrclaw.com/
My homepage: http://james.colannino.org/

" Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety." --Benjamin Franklin

Re: How to prototype functions that return pointers

[wwp]

Hello James,


On Fri, 24 Jun 2005 14:50:59 -0700 James Colannino <james@colannino.org>
wrote:

> Richard Nairn wrote:
> > Believe the correct decleration is (char *) readline();
> > 
> > Order of ops.
> 
> That was the next one I tried.  That yielded a syntax error.  I found
> out though that the "two or more data types" error was the result of a
> more difficult bug to find that had to do with something in another
> header file.  Once I fixed that, the declaration char * readline();
> worked.  Needless to say I'm very embarassed now... :-P

Moreover, the following ones are (should be) identical towards the C parser,
spaces between those tokens are not mandatory or can be repeated, and depend
on the coding style and recommendation/standard you follow:

char * readline();
char *readline();


Regards,

-- 
wwp

Re: How to prototype functions that return pointers

[Steve Graegert]

On 6/24/05, James Colannino <james@colannino.org> wrote:
> Ok, so this is a very embarassing question.  I tried googling for the
> answer but haven't figured it out yet, and everything I've tried results
> in compilation errors. I want to prototype a function that takes nothing
> as an argument but returns a pointer to a character.
> 
> I've tried the following:
> 
> char * readline();
> char *readline();

I can't see a problem with this declaration, thus I am not able to
reproduce the error(s).  What I see here is a function taking an
arbitrary number of arguments returning a pointer to a char.

> These first two result in 4 errors, each one identical and each one
> telling me "error: two or more data types in declaration of 'readline' "
> 
> *char readline();
> * char readline();

This is obviously wrong because you're trying to dereference a data
type, not an identifier. Everything else that follows in this line is
discarded by the parser.

I have compiled three different function declarations that all have a
different meaning to help you understand what could have been wrong:

/* pointer to func() returning a char */
char (*func)();

/* function taking a char pointer and returning char-pointer */
char* f(char *);

/* 
 * pointer to a function taking pointer to a char,
 * returning a pointer to a char
 */
char* (*fp)(char *);

Hope this clarifies the relations between pointers and functions and
their arguments.


Kind Regards

    \Steve

--

Steve Graegert <graegerts@gmail.com> || <http://www.technologies.de/~sg/>
Independent Software Consultant {C/C++ && Java && .NET}
Mobile: +49 (176)  21 24 88 69
Office: +49 (9131) 71 26 40 9

Re: How to prototype functions that return pointers

[Glynn Clements]

James Colannino wrote:

> Ok, so this is a very embarassing question.  I tried googling for the
> answer but haven't figured it out yet, and everything I've tried results
> in compilation errors. I want to prototype a function that takes nothing
> as an argument but returns a pointer to a character.

	char *myfunc(void);

> I've tried the following:
> 
> char * readline();
> char *readline();

Both of these declare a function taking unspecified arguments and
returning a char*. If the function takes no arguments, the argument
list should be declared as "void".

> These first two result in 4 errors, each one identical and each one
> telling me "error: two or more data types in declaration of 'readline' "

That error isn't related to your prototypes, but the context in which
they occur. In your follow-up, you note:

> I found
> out though that the "two or more data types" error was the result of a
> more difficult bug to find that had to do with something in another
> header file.

That seems likely.

-- 
Glynn Clements <glynn@gclements.plus.com>