portable typeof macro

[rkk]

Hi,

Is there an equivalent typeof macro/method to determine the type of a
variable in runtime & most importantly that works well with most known
C compilers?

gcc compiler supports typeof() macro, but the same code is not getting
compiled in solaris forte compiler and in microsoft VS 2003 compiler. I
tried something like below:

#include <stdio.h>

int
main()
{
int i;
typeof(i) j = 10;
i = j + 1;
printf("%d,%d\n ",i,j);
return 0;
}

The above code is just a test to see if the compiler supports typeof
macro/method. But only gcc supports it. I then tried __typeof__ which
is described in ISO standards I hope (I'm not sure btw), but again
supported by gcc and not by other compilers.

How does this typeof macro work? Or is there any equivalent
method/macro which is portable or that can be made portable to work
with all well known compilers.

Thanks in advance.

Best Regards
RKK

[Jack Klein]

On 25 Dec 2006 21:52:07 -0800, "rkk" <te*******@yaho o.comwrote in
comp.lang.c:

Hi,

Is there an equivalent typeof macro/method to determine the type of a
variable in runtime & most importantly that works well with most known
C compilers?

No, there is no such operator.

gcc compiler supports typeof() macro, but the same code is not getting
compiled in solaris forte compiler and in microsoft VS 2003 compiler. I
tried something like below:

#include <stdio.h>

int
main()
{
int i;
typeof(i) j = 10;
i = j + 1;
printf("%d,%d\n ",i,j);
return 0;
}

There is no such thing in C, nor is there any need for such a thing in
C.

The above code is just a test to see if the compiler supports typeof
macro/method. But only gcc supports it. I then tried __typeof__ which
is described in ISO standards I hope (I'm not sure btw), but again
supported by gcc and not by other compilers.

No, there is no __typeof__, or anything equivalent.

How does this typeof macro work? Or is there any equivalent

We have no idea how it works here, because it is not part of the C
language. However, it must be based on information that the compiler
has, and therefore the programmer has -- or can have -- as well.

method/macro which is portable or that can be made portable to work
with all well known compilers.

There is no such thing, but then again there really is no need for
such a thing in C.

Thanks in advance.

You are looking for something that does not exist, so you aren't going
to find it. What you should do is explain the problem you are trying
to solve, that you think you need such a feature would help with. Then
we can suggest ways of solving the problem.

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

[Keith Thompson]

"rkk" <te*******@yaho o.comwrites:

Is there an equivalent typeof macro/method to determine the type of a
variable in runtime & most importantly that works well with most known
C compilers?

gcc compiler supports typeof() macro, but the same code is not getting
compiled in solaris forte compiler and in microsoft VS 2003 compiler. I
tried something like below:

[snip]

"typeof" is not a macro; it's a gcc-specific keyword. It doesn't
exist in standard C, and there's no portable way to implement it in C.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Keith Thompson]

Jack Klein <ja*******@spam cop.netwrites:

On 25 Dec 2006 21:52:07 -0800, "rkk" <te*******@yaho o.comwrote in
comp.lang.c:

>Hi,

Is there an equivalent typeof macro/method to determine the type of a
variable in runtime & most importantly that works well with most known
C compilers?

No, there is no such operator.

>gcc compiler supports typeof() macro, but the same code is not getting
compiled in solaris forte compiler and in microsoft VS 2003 compiler. I
tried something like below:

#include <stdio.h>

int
main()
{
int i;
typeof(i) j = 10;
i = j + 1;
printf("%d,%d\n ",i,j);
return 0;
}

There is no such thing in C, nor is there any need for such a thing in
C.

[...]

Obviously there's no absolute need for it, since we've gotten along
for many years without it. But it could be useful in some contexts.
For example, you could use it to write a type-generic swap macro,
something like (untested code follows):

#define SWAP(a, b) do { \
typeof(a) tmp = a; b = a; a = tmp; \
} while(0)

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[jacob navia]

Keith Thompson a écrit :

"rkk" <te*******@yaho o.comwrites:

>>Is there an equivalent typeof macro/method to determine the type of a
variable in runtime & most importantly that works well with most known
C compilers?

gcc compiler supports typeof() macro, but the same code is not getting
compiled in solaris forte compiler and in microsoft VS 2003 compiler. I
tried something like below:

[snip]

"typeof" is not a macro; it's a gcc-specific keyword. It doesn't
exist in standard C, and there's no portable way to implement it in C.

It is not "gcc specific". Lcc-win32 supports the typeof macro

:-)

[Keith Thompson]

jacob navia <ja***@jacob.re mcomp.frwrites:

Keith Thompson a écrit :

[...]

>"typeof" is not a macro; it's a gcc-specific keyword. It doesn't
exist in standard C, and there's no portable way to implement it in C.

It is not "gcc specific". Lcc-win32 supports the typeof macro

Does lcc-win32 really implement "typeof" as a macro? How?

:-)

Or was that a joke?

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Denis Kasak]

Keith Thompson wrote:

Jack Klein <ja*******@spam cop.netwrites:

>There is no such thing in C, nor is there any need for such a thing in
C.

[...]

Obviously there's no absolute need for it, since we've gotten along
for many years without it. But it could be useful in some contexts.
For example, you could use it to write a type-generic swap macro,
something like (untested code follows):

#define SWAP(a, b) do { \
typeof(a) tmp = a; b = a; a = tmp; \
} while(0)

Correct me if I'm wrong, but wouldn't such a macro be limited to only
one appearance per variable scope? Should you use it more than once, you
would also be attempting to define a local variable with the same name
more than once (and possibly a different type also).

--
Denis Kasak

[Richard Heathfield]

Denis Kasak said:

Keith Thompson wrote:

<snip>

> #define SWAP(a, b) do { \
typeof(a) tmp = a; b = a; a = tmp; \
} while(0)

Correct me if I'm wrong, but wouldn't such a macro be limited to only
one appearance per variable scope? Should you use it more than once, you
would also be attempting to define a local variable with the same name
more than once (and possibly a different type also).

No, that's why it's all wrapped up in a { block scope }. The definition goes
out of scope at the closing brace.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.

[Denis Kasak]

Richard Heathfield wrote:

Denis Kasak said:

>Keith Thompson wrote:

<snip>

>> #define SWAP(a, b) do { \
typeof(a) tmp = a; b = a; a = tmp; \
} while(0)

Correct me if I'm wrong, but wouldn't such a macro be limited to only
one appearance per variable scope? Should you use it more than once, you
would also be attempting to define a local variable with the same name
more than once (and possibly a different type also).

No, that's why it's all wrapped up in a { block scope }. The definition goes
out of scope at the closing brace.

Right. Silly me. I'll never learn to refrain from posting this late.

--
Denis Kasak

[CBFalconer]

Denis Kasak wrote:

Keith Thompson wrote:

>Jack Klein <ja*******@spam cop.netwrites:

>>There is no such thing in C, nor is there any need for such a
thing in C.

[...]

Obviously there's no absolute need for it, since we've gotten
along for many years without it. But it could be useful in some
contexts. For example, you could use it to write a type-generic
swap macro, something like (untested code follows):

#define SWAP(a, b) do { \
typeof(a) tmp = a; b = a; a = tmp; \
} while(0)

Correct me if I'm wrong, but wouldn't such a macro be limited to
only one appearance per variable scope? Should you use it more
than once, you would also be attempting to define a local variable
with the same name more than once (and possibly a different type
also).

Consider yourself corrected. The declaration of tmp appears within
the block headed by the 'do' keyword, and is strictly local to that
block. After the closing '}' it no longer exists. That's why
Keith has wrapped it in the do while block.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>