Is this return UB ?

[dada]

Is this return UB ?
int someFunt ()
{
static int i = 0 ;

return i++ ;
}

WHat we want is the first time to return 0, next 1, etc

some thoughts ?

Thanks !
Joe
WB2JQT

----------------------
I tought my wife to drive a stick.
She learned to drive the broom all on her own.

[Richard Heathfield]

dada said:

Is this return UB ?
int someFunt ()
{
static int i = 0 ;

return i++ ;
}

WHat we want is the first time to return 0, next 1, etc

That's fine, until you hit INT_MAX. If you don't plan to get that high,
no problem.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[dada]

Richard Heathfield wrote:

dada said:

>>Is this return UB ?
int someFunt ()
{
static int i = 0 ;

return i++ ;
}

WHat we want is the first time to return 0, next 1, etc

That's fine, until you hit INT_MAX. If you don't plan to get that high,
no problem.

Thanks Richard.
I think there is more logic in the actual function for wrap around,
but the gist of the question was about what was returned.

Joe

[Jens Thoms Toerring]

dada <jb*****@stny.r r.comwrote:

Richard Heathfield wrote:

dada said:

>Is this return UB ?

int someFunt ()
{
static int i = 0 ;

return i++ ;
}

WHat we want is the first time to return 0, next 1, etc

That's fine, until you hit INT_MAX. If you don't plan to get that high,
no problem.

I think there is more logic in the actual function for wrap around,
but the gist of the question was about what was returned.

Sorry, but actually you didn't ask a question (or perhaps there
is but my English isn't up to it). If the question is what the
function returns on the very first call then the answer is 0.
And the return value the second time you call it is 1 (the post-
fix ++ operator is only applied after the value of the expres-
sion has been evaluated).
Regards, Jens
--
\ Jens Thoms Toerring ___ [e-mail]
\______________ ____________ http://toerring.de

[Richard Heathfield]

Jens Thoms Toerring said:

dada <jb*****@stny.r r.comwrote:

>Richard Heathfield wrote:

dada said:

Is this return UB ?

int someFunt ()
{
static int i = 0 ;

return i++ ;
}

WHat we want is the first time to return 0, next 1, etc

That's fine, until you hit INT_MAX. If you don't plan to get that
high, no problem.

I think there is more logic in the actual function for wrap around,
but the gist of the question was about what was returned.

Sorry, but actually you didn't ask a question (or perhaps there
is but my English isn't up to it).

Well, actually he did - he asked if the return statement invoked "UB" -
i.e. undefined behaviour (see above). It doesn't, as long as overflow
doesn't occur. He also pointed out what he wanted. My answer ("That's
fine..." - see above) covered both his explicit question and his
implicit request. Sorry if I didn't make this clearer.

If the question is what the
function returns on the very first call then the answer is 0.
And the return value the second time you call it is 1 (the post-
fix ++ operator is only applied after the value of the expres-
sion has been evaluated).

Er, kindasortakinda , yes. Actually, there's nothing to stop the compiler
doing something like:

INC I
MOV R1, I
DEC R1
RET

(other than the bounds of common sense, of course).

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[@$|-|. DUBEY]

declare
static int var = 0;
as global variable not auto variable.....

and
return ( var++ )
now each calling will increment it

for eg.

#include<stdio. h>
static int x = 0;
int ret( void );

int main( void )
{
int i;
for ( i = 0; i < 100; i++ )
{
ret( );
printf( "%d\n", x );
}
_getch( );
return ( 0 );
}

int ret( void )
{
return( x ++ );
}

[Richard Heathfield]

@$|-|. DUBEY said:

declare
static int var = 0;
as global variable

Why? What benefit does it confer that overcomes the disadvantage of its
being defined at file scope?

not auto variable.....

He didn't define it as an auto object. Here's his code again:

int someFunt ()
{
static int i = 0 ;

return i++ ;
}

i has static storage duration, not automatic storage duration.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Richard]

Richard Heathfield <rj*@see.sig.in validwrites:

Jens Thoms Toerring said:

>dada <jb*****@stny.r r.comwrote:

>>Richard Heathfield wrote:
dada said:

Is this return UB ?

int someFunt ()
{
static int i = 0 ;

return i++ ;
}

WHat we want is the first time to return 0, next 1, etc

That's fine, until you hit INT_MAX. If you don't plan to get that
high, no problem.

I think there is more logic in the actual function for wrap around,
but the gist of the question was about what was returned.

Sorry, but actually you didn't ask a question (or perhaps there
is but my English isn't up to it).

Well, actually he did - he asked if the return statement invoked "UB" -
i.e. undefined behaviour (see above). It doesn't, as long as overflow
doesn't occur. He also pointed out what he wanted. My answer ("That's
fine..." - see above) covered both his explicit question and his
implicit request. Sorry if I didn't make this clearer.

>If the question is what the
function returns on the very first call then the answer is 0.
And the return value the second time you call it is 1 (the post-
fix ++ operator is only applied after the value of the expres-
sion has been evaluated).

Er, kindasortakinda , yes. Actually, there's nothing to stop the compiler
doing something like:

INC I
MOV R1, I
DEC R1
RET

(other than the bounds of common sense, of course).

That is totally platform dependant and therefore ... you know.

As far as C goes, he was right. The ++ is applied to "i" after the value
of I is evaluated and handed to the return statement. There is no need
whatsoever to obfuscate this.

To the OP. You code does not exhibit "UB" until overflow. And then its
platform specific I believe.

[Jack Klein]

On Fri, 27 Jul 2007 07:31:22 -0700, "@$|-|. DUBEY"
<du***********@ gmail.comwrote in comp.lang.c:

declare
static int var = 0;
as global variable not auto variable.....

No, there is no gain and some loss to changing his already correct
definition of a static object at function scope. While it is
permissible to initialize a static scalar object with 0, it is
unnecessary and redundant.

and
return ( var++ )
now each calling will increment it

for eg.

#include<stdio. h>
static int x = 0;
int ret( void );

int main( void )
{
int i;
for ( i = 0; i < 100; i++ )
{
ret( );
printf( "%d\n", x );
}
_getch( );

There is no such function as "_getch" in C.

return ( 0 );

"return" is a statement, not a function. Remove the parentheses.

}

int ret( void )
{
return( x ++ );

Again, remove the parentheses. They haven't been required for 18
years.

--
Jack Klein
Home: http://JK-Technology.Com
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comp.lang.c http://c-faq.com/
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alt.comp.lang.l earn.c-c++
http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html

[Old Wolf]

On Jul 28, 3:05 pm, Jack Klein <jackkl...@spam cop.netwrote:

While it is permissible to initialize a static scalar
object with 0, it is unnecessary and redundant.

I think it helps the code readability.