linking C++ functions in a C program

[abasili]

Hi everyone, I'm trying to compile a C++ function and then call it from
a C program.
Since Google is my friend I've ended up to this link which seems very clear:

http://www.parashift.com/c++-faq-lit...c-and-cpp.html

Unfortunately it does not work.
Here is what I'm doing:

-----------------------------------------
//main.c

#include "mylib.h"

int main (int argc, char *argv[]){
foo();
return 0;
}
-----------------------------------------
//mylib.h

#indef __cplusplus
extern "C"{
#endif

void foo();

#ifdef __cplusplus
}
#endif
-----------------------------------------
//mylib.cc

#include <iostream>
#include "mylib.h"

using namespace std; // don't know what for!

void foo(){
cout<<"Hello World!\n";
}
-----------------------------------------
Thanks a lot for any suggestion.

Al

[Pawel Dziepak]

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CBFalconer wrote:

In general, you just can't do that. C++ function names are
normally altered by the C++ compiler for various reasons. C
function names are not. So the C system can't link the C++ code.

7.5/3 states that: "Every implementation shall provide for linkage to
functions written in the C programming language" by allowing things like
extern "C"
7.5/6 tells us that is is possible to define function with C-style
linkage in C++ code.
7.5/9 informs us that implementation can allow to link objects from
other languages to C++ and from C++ to other languages.

Concluding, C++ standard gives possibility to link C++ functions from C
code (with some naming restrictions).

Pawel Dziepak
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[Keith Thompson]

CBFalconer <cb********@yah oo.comwrites:

abasili wrote:

>Ian Collins wrote:

>>It does if you follow all the points. The first two are often
overlooked.

I'm sorry about that, actually compiling with g++ the main works.
The main problem is that my C program cannot be compiled with g++,
there are too many incompatibiliti es and a lot of work has been
already done in C. So I have to find another way to call a C++
function through my C code.

In general, you just can't do that. C++ function names are
normally altered by the C++ compiler for various reasons. C
function names are not. So the C system can't link the C++ code.

Chuck, we've had this discussion before. Yes, you can call C++
functions from C, and yes, you can call C functions from C++. C++
defines the mechanism for doing this in both directions.

Last time we discussed this, I pointed you to the C++ FAQ that
explains this; it's already been cited in this thread. I even
demonstrated how to do it and posted the output. For some reason you
still didn't believe me, and now you're claiming yet again that it
can't be done.

Please consider the possibility that you might be wrong.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Flash Gordon]

CBFalconer wrote, On 06/11/08 21:54:

<snip>

describes the access to the C code required. In general C++ can
access C code, but C cannot access C++ code.

Remember, the languages are different.

Remember, it has been pointed out to you many times and with references
that you are WRONG. C++ defines how C code can call C++ code and you
have been shown how it works. Since the theory says it should work and
practice shows that it works why keep insisting that it does not?
Neither theory nor practice are on your side.
--
Flash Gordon
If spamming me sent it to sm**@spam.cause way.com
If emailing me use my reply-to address
See the comp.lang.c Wiki hosted by me at http://clc-wiki.net/

[Bill Reid]

Keith Thompson <ks***@mib.orgw rote in message
news:ln******** ****@nuthaus.mi b.org...

CBFalconer <cb********@yah oo.comwrites:

abasili wrote:

Ian Collins wrote:

It does if you follow all the points. The first two are often
overlooked.

I'm sorry about that, actually compiling with g++ the main works.
The main problem is that my C program cannot be compiled with g++,
there are too many incompatibiliti es and a lot of work has been
already done in C. So I have to find another way to call a C++
function through my C code.

In general, you just can't do that. C++ function names are
normally altered by the C++ compiler for various reasons. C
function names are not. So the C system can't link the C++ code.

Chuck, we've had this discussion before. Yes, you can call C++
functions from C, and yes, you can call C functions from C++. C++
defines the mechanism for doing this in both directions.

Last time we discussed this, I pointed you to the C++ FAQ that
explains this; it's already been cited in this thread. I even
demonstrated how to do it and posted the output. For some reason you
still didn't believe me, and now you're claiming yet again that it
can't be done.

Please consider the possibility that you might be wrong.

Please consider the possibility that he might be
<sotto voce>insane</sotto voce>.

I mean, there is a total nadir of Usenet kookery, the
murky abyss where sense is nonsense and right is wrong
and reality can never escape the intense gravitational pull of
the completely collapsed nuerons of the infernally eternally
defiantly dense.

Also, please consider the possibility that YOU might
be insane if you ever try to correct him on this or the many
other topics he is wrong, according to this widely-accepted
measure:

"Insanity is doing the same thing over and over again and
expecting a different result."

---
William Ernest Reid

[James Kuyper]

Flash Gordon wrote:

CBFalconer wrote, On 06/11/08 21:54:

If you're responding to what he wrote at that time, why don't you post
it as a response to the message in which he actually wrote it, on the
thread in which he wrote it? It's a little confusing to post it as a
response to a message I wrote, in a thread where he's said some
incorrect things about C/C++ linking, but he hasn't actually said these
particular incorrect things (at least, not yet):

>describes the access to the C code required. In general C++ can
access C code, but C cannot access C++ code.

[Stephen Sprunk]

CBFalconer wrote:

abasili wrote:

>Ian Collins wrote:

>>It does if you follow all the points. The first two are often
overlooked.

I'm sorry about that, actually compiling with g++ the main works.
The main problem is that my C program cannot be compiled with g++,
there are too many incompatibiliti es and a lot of work has been
already done in C. So I have to find another way to call a C++
function through my C code.

In general, you just can't do that. C++ function names are
normally altered by the C++ compiler for various reasons. C
function names are not. So the C system can't link the C++ code.

If you mean "in general" to mean "in the normal case where extern "C" is
not used", you are correct. However, I am confident that you know C++
provides that mechanism to disable function name mangling, so your
answer is deliberately misleading. You'd have been better off simply
declaring it OT, as this entire thread has been from the beginning.

S

[CBFalconer]

Flash Gordon wrote:

CBFalconer wrote, On 06/11/08 21:54:

<snip>

>describes the access to the C code required. In general C++ can
access C code, but C cannot access C++ code.

Remember, the languages are different.

Remember, it has been pointed out to you many times and with
references that you are WRONG. C++ defines how C code can call
C++ code and you have been shown how it works. Since the theory
says it should work and practice shows that it works why keep
insisting that it does not? Neither theory nor practice are on
your side.

I sent some answers, but something has fouled, and they are not
here.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

[Phil Carmody]

Ian Collins <ia******@hotma il.comwrites:

abasili wrote:

>Hi everyone, I'm trying to compile a C++ function and then call it from
a C program.
Since Google is my friend I've ended up to this link which seems very
clear:

http://www.parashift.com/c++-faq-lit...c-and-cpp.html

Unfortunatel y it does not work.

It does if you follow all the points. The first two are often overlooked.

Some would say it's impossible. If you are building the final
executable (main and linking) with a C++ compiler, then they
might say that you are building a C++ program that calls C
functions. However, what was required was instead a C program
which calls C++ functions. If you're careful to avoid anything
too C++-like, then C++ can be incorporated into C, but then
you're hamstrung a bit with what you can do in C++, and what's
the point. So I'd say stick C into C++, not the other way round.

Phil
--
We must respect the other fellow's religion, but only in the sense and to the
extent that we respect his theory that his wife is beautiful and his children
smart. -- Henry Louis Mencken (1880-1956), American editor and critic

[Flash Gordon]

CBFalconer wrote, On 06/11/08 22:07:

Pawel Dziepak wrote:

>CBFalconer wrote:

>>In general, you just can't do that. C++ function names are
normally altered by the C++ compiler for various reasons. C
function names are not. So the C system can't link the C++ code.

7.5/3 states that: "Every implementation shall provide for linkage
to functions written in the C programming language" by allowing
things like extern "C"
7.5/6 tells us that is is possible to define function with C-style
linkage in C++ code.
7.5/9 informs us that implementation can allow to link objects from
other languages to C++ and from C++ to other languages.

Concluding, C++ standard gives possibility to link C++ functions
from C code (with some naming restrictions).

You are quoting from, I believe, the C++ standard.

Yes he is, because that is what defines how to do it.

My point is
that C cannot call to C++ code, but C++ can call C code.

Which is EXACTLY what is wrong.

The idea
is to prepare C object code and allow the C++ system to call it
correctly, by using the extern "C" identification _in the header
file for the C code_.

1) You don't have to modify the C headers

extern "C" {
#include "c-header"
}

2) You have already been shown how to use the mechanisms defined in C++
to call C++ from C. These mechanisms to not violate the C standard any
more than any other library being callable from C does.

The C++ standard is meaningless in c.l.c. Here, we use the C std.

You can tell people that if they want to discuss it to go to
comp.lang.c++, however telling people something that is just plain WRONG
rather than redirecting people where you do not know any better is what
the trolls do. If you don't know about something, either redirect people
to an appropriate group or don't say anything.
--
Flash Gordon
If spamming me sent it to sm**@spam.cause way.com
If emailing me use my reply-to address
See the comp.lang.c Wiki hosted by me at http://clc-wiki.net/

[Flash Gordon]

Keith Thompson wrote, On 07/11/08 02:49:

James Kuyper <ja*********@ve rizon.netwrites :

>Flash Gordon wrote:

>>CBFalconer wrote, On 06/11/08 21:54:

If you're responding to what he wrote at that time, why don't you post
it as a response to the message in which he actually wrote it, on the
thread in which he wrote it? It's a little confusing to post it as a
response to a message I wrote, in a thread where he's said some
incorrect things about C/C++ linking, but he hasn't actually said
these particular incorrect things (at least, not yet):

>>>describes the access to the C code required. In general C++ can
access C code, but C cannot access C++ code.

James, either I'm confused or you are.

You are not confused, James is.

<snip>

Flash's article was a direct followup to CBFalconer's article, and
CBFalconer did write exactly the quoted incorrect words:

describes the access to the C code required. In general C++ can
access C code, but C cannot access C++ code.

Remember, the languages are different.

Did the "06/11/08" date format throw you off? It's DD/MM/YY, not
MM/DD/YY -- i.e., it's today, not 5 months ago. (MM/DD/YY is more
common in the US, DD/MM/YY in the UK; that's why I use YYYY-MM-DD
whenever possible.)

Yes, I should probably look at how to change it.
--
Flash Gordon
If spamming me sent it to sm**@spam.cause way.com
If emailing me use my reply-to address
See the comp.lang.c Wiki hosted by me at http://clc-wiki.net/