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I think this problem relates to either c or c++ ( but I am not sure which
one ) so I post to both of these news group. I am sorry if I did something
wrong here.

Is there any difference between these two declarations :

1.
void * functionA( char * p, int s, int * e );

and
2.
typedef void * ( *functionA_t)( char * p, int s, int * e );
functionA_t functionA();

I thought they are the same, but I must be wrong somewhere. The function is
compiled and linked into a .so file. For the first declarartion, nm(1)
shows that name in the .so file, but not for the 2nd declaration.

Each of these declaration is embraced by extern "C" { }. The implenetation
file is a .cpp compiled with g++.

Thanks,

Vu

Vu Pham <> scribbled the following
on comp.lang.c:
> I think this problem relates to either c or c++ ( but I am not sure which
> one ) so I post to both of these news group. I am sorry if I did something
> wrong here.

> Is there any difference between these two declarations :

> 1.
> void * functionA( char * p, int s, int * e );

> and
> 2.
> typedef void * ( *functionA_t)( char * p, int s, int * e );
> functionA_t functionA();

Yes, there is. The first declares a function taking three arguments,
of types (char *), (int) and (int *), and returning a (void *).
The second declares a function taking an unspecified number of
arguments, and returning a pointer to a function that is declared as
in the first case.
That's a pretty fundamental difference.

> I thought they are the same, but I must be wrong somewhere. The function is
> compiled and linked into a .so file. For the first declarartion, nm(1)
> shows that name in the .so file, but not for the 2nd declaration.

They are not the same as all. Maybe that's why you are getting
different results.
Note that .so files and nm(1) are off-topic here.

> Each of these declaration is embraced by extern "C" { }. The implenetation
> file is a .cpp compiled with g++.

This smacks of C++, which is also off-topic here. But I can say that
the same I said above applies for C++, with one difference: replace
"an unspecified number of arguments" with "no arguments".

--
/-- Joona Palaste () ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"'I' is the most beautiful word in the world."
- John Nordberg

Joona I Palaste <> scribbled the following
on comp.lang.c:
> Vu Pham <> scribbled the following
> on comp.lang.c:
>> Is there any difference between these two declarations :

>> 1.
>> void * functionA( char * p, int s, int * e );

>> and
>> 2.
>> typedef void * ( *functionA_t)( char * p, int s, int * e );
>> functionA_t functionA();

>> I thought they are the same, but I must be wrong somewhere. The function is
>> compiled and linked into a .so file. For the first declarartion, nm(1)
>> shows that name in the .so file, but not for the 2nd declaration.

> They are not the same as all. Maybe that's why you are getting
> different results.
> Note that .so files and nm(1) are off-topic here.

I meant "not the same at all". Sorry for the confusing typo.

--
/-- Joona Palaste () ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"C++. C++ run. Run, ++, run."
- JIPsoft

Vu Pham wrote:
> I think this problem relates to either c or c++ ( but I am not sure which
> one ) so I post to both of these news group. I am sorry if I did something
> wrong here.
>
> Is there any difference between these two declarations :
>
> 1.
> void * functionA( char * p, int s, int * e );
>
> and
> 2.
> typedef void * ( *functionA_t)( char * p, int s, int * e );
> functionA_t functionA();
>
> I thought they are the same, but I must be wrong somewhere. The function is
> compiled and linked into a .so file. For the first declarartion, nm(1)
> shows that name in the .so file, but not for the 2nd declaration.
>
> Each of these declaration is embraced by extern "C" { }. The implenetation
> file is a .cpp compiled with g++.
>
> Thanks,
>
> Vu
>

It's the same as the difference between:

extern int a;
and
int *a;

The first one is a declaration of an integer.
The second one defines a variable of type pointer to int.

In your first example, functionA the declaration of a function
returning void*, taking char *, int, and int*

In your second example functionA is a POINTER TO A FUNCTION returning
void*, taking char *, int, and int*

Does that make some sense?

red floyd <> scribbled the following
on comp.lang.c:
> Vu Pham wrote:
>> I think this problem relates to either c or c++ ( but I am not sure which
>> one ) so I post to both of these news group. I am sorry if I did something
>> wrong here.
>>
>> Is there any difference between these two declarations :
>>
>> 1.
>> void * functionA( char * p, int s, int * e );
>>
>> and
>> 2.
>> typedef void * ( *functionA_t)( char * p, int s, int * e );
>> functionA_t functionA();
>>
>> I thought they are the same, but I must be wrong somewhere. The function is
>> compiled and linked into a .so file. For the first declarartion, nm(1)
>> shows that name in the .so file, but not for the 2nd declaration.
>>
>> Each of these declaration is embraced by extern "C" { }. The implenetation
>> file is a .cpp compiled with g++.

> It's the same as the difference between:

> extern int a;
> and
> int *a;

No, it isn't.

> The first one is a declaration of an integer.
> The second one defines a variable of type pointer to int.

> In your first example, functionA the declaration of a function
> returning void*, taking char *, int, and int*

> In your second example functionA is a POINTER TO A FUNCTION returning
> void*, taking char *, int, and int*

Note the () after the symbol functionA. This makes functionA
*A FUNCTION* returning the pointer to a function you defined above.

> Does that make some sense?

Pretty much... =)

--
/-- Joona Palaste () ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Normal is what everyone else is, and you're not."
- Dr. Tolian Soran

"Joona I Palaste" <> wrote in message
news:bu49ok$dqi$...
> Vu Pham <> scribbled the following
> on comp.lang.c:
> > I think this problem relates to either c or c++ ( but I am not sure
which
> > one ) so I post to both of these news group. I am sorry if I did
something
> > wrong here.
>
> > Is there any difference between these two declarations :
>
> > 1.
> > void * functionA( char * p, int s, int * e );
>
> > and
> > 2.
> > typedef void * ( *functionA_t)( char * p, int s, int * e );
> > functionA_t functionA();
>
> Yes, there is. The first declares a function taking three arguments,
> of types (char *), (int) and (int *), and returning a (void *).
> The second declares a function taking an unspecified number of
> arguments, and returning a pointer to a function that is declared as
> in the first case.
> That's a pretty fundamental difference.

Thanks for the explanation.

Shame one me

My problem is :
I need to use the declaration of typedef as in 2, and I also need to
declare the functionA like declared in 1, but with the definition of
functionA_t so that whenever I change functionA_t functionA declaration
will be changed correspondingly.

How do I do that ?

Thanks,

Vu

"Vu Pham" <> wrote in message news:bu49bv$dddep$...
>
> Is there any difference between these two declarations :
>
> 1.
> void * functionA( char * p, int s, int * e );
>
> and
> 2.
> typedef void * ( *functionA_t)( char * p, int s, int * e );
> functionA_t functionA();

Yes, the second defines a function called functionA that returns a pointer
to function. functionA_t is type pointer to function.

You could
typedef void (functionA_t) (char*, int, int*);
functionA_t functionA; // note no parens.

> In your second example functionA is a POINTER TO A FUNCTION returning
> void*, taking char *, int, and int*

Nope, actually it's a function returning the above pointer-to-function.

"Joona I Palaste" <> wrote in message news:bu49ok$dqi$...
> The second declares a function taking an unspecified number of
> arguments, and returning a pointer to a function that is declared as
> in the first case.

Actually it's a function taking NO arguments (not an unspecified number
of arguments) in C++. The original poster needs to figure out what language
he is programming in.

"Ron Natalie" <> wrote in message
news:400566ab$0$71362$ m...
>
> "Joona I Palaste" <> wrote in message
news:bu49ok$dqi$...
> > The second declares a function taking an unspecified number of
> > arguments, and returning a pointer to a function that is declared as
> > in the first case.
>
> Actually it's a function taking NO arguments (not an unspecified number
> of arguments) in C++. The original poster needs to figure out what
language
> he is programming in.
>

I use c++ for the implementation file, but that function needs to be
exported ( from an.so ) and I use extern "C" { } in the declaration file (
..h ) to prevent the name mangling.

Vu