What is the purpose of such a function ?

[Razvan]

Hi!

What is the purpose of such a function ?
int function(void)
{

return 1;
}

It seems to be completely equivalent with
int function()
{

return 1;
}

Is its behaviour different on a C versus a C++ compiler ?

Regards,
Razvan

[Dan Pop]

In <15************ **************@ posting.google. com> mi*****@mailcit y.com (Razvan) writes:

What is the purpose of such a function ?

int function(void)
{
return 1;
}

It seems to be completely equivalent with

int function()
{
return 1;
}

Is its behaviour different on a C versus a C++ compiler ?

Yes. On a C compiler, the latter is an old style function definition,
that doesn't provide a prototype for the function:

fangorn:~/tmp 183> cat test.c
int function() { return 0; }

int main() { return function(2, 3); }
fangorn:~/tmp 184> gcc test.c
fangorn:~/tmp 185> g++ test.c
test.c: In function `int main()':
test.c:1: error: too many arguments to function `int function()'
test.c:3: error: at this point in file

The original version has identical semantics under both C and C++.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[kal]

mi*****@mailcit y.com (Razvan) wrote in message news:<15******* *************** ****@posting.go ogle.com>...

What is the purpose of such a function ?

int function(void)
{

return 1;
}

It seems to be completely equivalent with

int function()
{

return 1;
}

Is its behaviour different on a C versus a C++ compiler ?

I think so.

In C: "int f(void);" delcares a function with NO parameters
returning an int. "int f();" declares a function with no
parameter SPECIFICATION returning an int.

[Dan Pop]

In <a5************ **************@ posting.google. com> k_*****@yahoo.c om (kal) writes:

In C: "int f(void);" delcares a function with NO parameters
returning an int. "int f();" declares a function with no
parameter SPECIFICATION returning an int.

Well, it still specifies something: that the unknown number of parameters
of unknown types is fixed, i.e. f() cannot be a variadic function.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[S.Tobias]

Dan Pop <Da*****@cern.c h> wrote:

In <a5************ **************@ posting.google. com> k_*****@yahoo.c om (kal) writes:

In C: "int f(void);" delcares a function with NO parameters
returning an int. "int f();" declares a function with no
parameter SPECIFICATION returning an int.

Well, it still specifies something: that the unknown number of parameters
of unknown types is fixed, i.e. f() cannot be a variadic function.

It seems (by experiment) that you can make both f(2,3) and f(2,3,4)
calls in the same function main().
Then is it possible (or was it in the "old style") to define:
int f(int n, ...) { /*...*/ }
and declare in the header:
int f();
?

--
Stan Tobias

[Dan Pop]

In <2j************ *@uni-berlin.de> "S.Tobias" <sN*******@amu. edu.pl> writes:

Dan Pop <Da*****@cern.c h> wrote:

In <a5************ **************@ posting.google. com> k_*****@yahoo.c om (kal) writes:

>In C: "int f(void);" delcares a function with NO parameters
>returning an int. "int f();" declares a function with no
>parameter SPECIFICATION returning an int.

Well, it still specifies something: that the unknown number of parameters
of unknown types is fixed, i.e. f() cannot be a variadic function.

It seems (by experiment) that you can make both f(2,3) and f(2,3,4)
calls in the same function main().

At least one of them invokes undefined behaviour.
Then is it possible (or was it in the "old style") to define:
int f(int n, ...) { /*...*/ }
and declare in the header:
int f();
?

The ellipsis thing didn't exist at all pre-ANSI. On implementations
supporting the <varargs.h> interface, you'd declare it as

int f();

and define it like this:

#include <varargs.h>

int f(va_alist)
va_dcl /* no semicolon */
{
...
}

The actual mechanism for accessing the parameter list was relatively
similar to the one provided by <stdarg.h>.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[S.Tobias]

Dan Pop <Da*****@cern.c h> wrote:

of unknown types is fixed, i.e. f() cannot be a variadic function.

Could you, please, give me the place in the Standard that supports this?

I'm not challenging your claim at all. I've checked on-line como
and it refuses to take
int f();
int f(int i, ...) { return 0; }
both in C90 and C99 mode.
But OTOH I've searched through the Standard and the only explicit
statement about this I could find is a note in 7.15.1.4#6 in an
example for va_start macro:
[...]
void f1(int n_ptrs, ...)
{
[...]
}
Each call to f1 is required to have visible the definition of the
function or a declaration such as
void f1(int, ...);
But AFAIK examples are not normative.
It seems (by experiment) that you can make both f(2,3) and f(2,3,4)
calls in the same function main().

At least one of them invokes undefined behaviour.
What I meant is that gcc didn't protest. I thought that the compiler
might be wise enough to notice different number of arguments, if it
were an issue. Since it didn't (neither did como btw), I thought it
might consider f() variadic, which led me to next question.
Then is it possible (or was it in the "old style") to define:
int f(int n, ...) { /*...*/ }
and declare in the header:
int f();
?

The ellipsis thing didn't exist at all pre-ANSI. On implementations
supporting the <varargs.h> interface, you'd declare it as

[snip]

Thank you!

--
Stan Tobias

[Ralmin]

"S.Tobias" <sN*******@amu. edu.pl> wrote:

Dan Pop <Da*****@cern.c h> wrote:

> of unknown types is fixed, i.e. f() cannot be a variadic function.

Could you, please, give me the place in the Standard that supports this?

What about 6.5.2.2 "Function Calls", paragraph 6?

"If the expression that denotes the called function has a type that
does not include a prototype, the integer promotions are performed
on each argument, and arguments that have type float are promoted
to double. These are called the default argument promotions. If the
number of arguments does not equal the number of parameters, the
behavior is undefined. If the function is defined with a type that
includes a prototype, and either the prototype ends with an
ellipsis (, ...) or the types of the arguments after promotion are
not compatible with the types of the parameters, the behavior is
undefined."

This paragraph makes it undefined behaviour to call a variadic function
through an unprototyped declaration.

--
Simon.

[Jack Klein]

On 22 Jun 2004 21:22:55 GMT, "S.Tobias" <sN*******@amu. edu.pl> wrote
in comp.lang.c:

Dan Pop <Da*****@cern.c h> wrote:

> of unknown types is fixed, i.e. f() cannot be a variadic function.
Could you, please, give me the place in the Standard that supports this?
It is not easy to parse it out, but it is in C99 6.5.2.2, P6 which
talks about calls to functions that do not have a prototype (although
in C99 they must have at least a declaration):

[begin quote]

If the expression that denotes the called function has a type that
does not include a prototype, the integer promotions are performed on
each argument, and arguments that have type float are promoted to
double. These are called the default argument promotions. If the
number of arguments does not equal the number of parameters, the
behavior is undefined. If the function is defined with a type that
includes a prototype, and either the prototype ends with an ellipsis
(, ...) or the types of the arguments after promotion are not
compatible with the types of the parameters, the behavior is
undefined.

[end quote]

So if you call a function without a prototype in scope and it is
variadic (i.e., it is defined with an argument list ending in ", ...",
the behavior is specifically undefined.

I'm not challenging your claim at all. I've checked on-line como
and it refuses to take
int f();
int f(int i, ...) { return 0; }
both in C90 and C99 mode.
But OTOH I've searched through the Standard and the only explicit
statement about this I could find is a note in 7.15.1.4#6 in an
example for va_start macro:
[...]
void f1(int n_ptrs, ...)
{
[...]
}
Each call to f1 is required to have visible the definition of the
function or a declaration such as
void f1(int, ...);
But AFAIK examples are not normative.
It seems (by experiment) that you can make both f(2,3) and f(2,3,4)
calls in the same function main().

At least one of them invokes undefined behaviour.

What I meant is that gcc didn't protest. I thought that the compiler
might be wise enough to notice different number of arguments, if it
were an issue. Since it didn't (neither did como btw), I thought it
might consider f() variadic, which led me to next question.

Remember, the standard places no requirements at all in cases of
undefined behavior. An implementation is allowed, but not required,
to emit a diagnostic for undefined behavior. But it is also allowed,
but not required, to emit a diagnostic for any reason at all.

i.e.:

# ds2kc welldefined.c
Death Station 2000 C2009 Compiler Version 1.0
compiling welldefined.c.. .
Lovely weather we're having today, isn't it?
0 errors
#

The wording in C89/90 was similar, although it had text allowing for
implicit declaration of functions returning int.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
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alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[Razvan]

> >What is the purpose of such a function ?

int function(void)
{
return 1;
}

It seems to be completely equivalent with

int function()
{
return 1;
}

Is its behaviour different on a C versus a C++ compiler ?

Yes. On a C compiler, the latter is an old style function definition,
that doesn't provide a prototype for the function:

fangorn:~/tmp 183> cat test.c
int function() { return 0; }

int main() { return function(2, 3); }
fangorn:~/tmp 184> gcc test.c
fangorn:~/tmp 185> g++ test.c
test.c: In function `int main()':
test.c:1: error: too many arguments to function `int function()'
test.c:3: error: at this point in file

The original version has identical semantics under both C and C++.

You are able to compile the code with the C compiler (gcc) but
not with the C++ compiler (g++).

That means:
1. int f(void)
Under both C and C++ languages it is a function that takes no
parameters and return an int;

2. int f()
in C - a function that takes ANY number of parameters;
in C++ - a function that takes NO parameters.

So, if you want to write a function that takes no parameters
that is valid C & C++ code you should write:

int f(void)

Thanks,
Razvan