[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.c++

Question about mixing c++ exception handling & c code

abhijeet

11/24/2008 7:07:00 PM

Hi,

I was looking thru code in my organisation. same dll is sharingcode is
mixing c++ code & c code, which is being again called by some other c+
+ dll.

Only issue I am not too sure about exception handling in this case -

here is trimmed code snippet -

include.h
typedef void (func*)(void *,bool);
struct scriptparams
{
func callback;
void *obj;
};

test.cpp
class execption
{
public:
virtual void printerror(){//do something};
};
class foo
{
public:
foo(){};
void dosomething(bool arg)
{
cout>>"do something">>endl;
if(!arg) throw execption;
//if valid do something
};
};
extern "C" void dosomethingwrapper(void *obj_,bool arg)
{
foo *fooptr = reinterpret_cast<foo*>obj_;
fooptr->dosomething(arg);
};

test1.c
#include <include.h>
void
executescript(scriptparams* params)
{
bool ifValid = false;
//calculate something to get value of
params->callback(params->obj,ifValid);
}

test2.cpp
#include <include.h>
class scriptexecuter
{
public:
scriptexecuter(char* arg1,char* arg2)
{// get these args & do someprocessing};
void execute()
{
scriptparams params;
params->callback = dosomethingwrapper;
params->obj = this;
try{
executescript(params);
}
catch(execption &e)
{
e.printerror();
}
};
};

test.cpp & test1.c are being compiled in one dll lets call dll1 & othe
being compiled into another dll -> dll2.

I am not sure what to expect if foo::dosomething raises an exception.
Is code safe for exception being traversing through c code.
Can I assume object which is being caught in scriptexecuter::execute
to be properly constructed one.

Thank you for your advice.

Regards,
Abhijeet
6 Answers

Paavo Helde

11/24/2008 8:06:00 PM

0

abhijeet <abhi.10dulkar@gmail.com> kirjutas:

> Hi,
>
> I was looking thru code in my organisation. same dll is sharingcode is
> mixing c++ code & c code, which is being again called by some other c+
> + dll.
>
> Only issue I am not too sure about exception handling in this case -

Passing C++ exceptions through C code is undefined behavior. You can
easily got a segfault or something worse.

The implementation may define the behavior, though. Most notably, MSVC++
does, as C++ exceptions are implemented on top of Windows OS-level
"structured exceptions" which are also supported in C. However, to handle
them properly (like releasing any held resources during stack backwind),
the C code must use non-standard extensions for exception handling by
itself, and I'm by some reason quite sure it often doesn't. I.e. you can
use this technique only in the case when the C interface explicitly
documents that it supports C++ exceptions (that is, on this specific
platform).

For handling C++ exceptions portably, any C++ function which might be
called from C code should catch all exceptions and not let thenm
propagate to the C code. For example, it can convert them into error
codes or log them somewhere else.

hth
Paavo

Peter

11/24/2008 10:22:00 PM

0

On Nov 24, 11:07 am, abhijeet <abhi.10dul...@gmail.com> wrote:
> Hi,
>
> I was looking thru code in my organisation. same dll is sharingcode is
> mixing c++ code & c code, which is being again called by some other c+
> + dll.


There is no need to translate any code with a c-compiler.
Ansi C code compiles with a C++-compiler.
My advice is to get rid of C code in favor or exception-safe-C++ code.

Peter

11/24/2008 10:29:00 PM

0

On Nov 24, 11:07 am, abhijeet <abhi.10dul...@gmail.com> wrote:
> I am not sure what to expect if foo::dosomething raises an exception.
> Is code safe for exception being traversing through c code.


As long as the C-code is being translated using a C++ compiler you're
fine.

Ian Collins

11/25/2008 6:39:00 AM

0

Peter wrote:
> On Nov 24, 11:07 am, abhijeet <abhi.10dul...@gmail.com> wrote:
>> Hi,
>>
>> I was looking thru code in my organisation. same dll is sharingcode is
>> mixing c++ code & c code, which is being again called by some other c+
>> + dll.
>
>
> There is no need to translate any code with a c-compiler.
> Ansi C code compiles with a C++-compiler.

No, it does not. There's plenty of legal C that isn't legal C++.

--
Ian Collins

Ian Collins

11/25/2008 6:39:00 AM

0

Peter wrote:
> On Nov 24, 11:07 am, abhijeet <abhi.10dul...@gmail.com> wrote:
>> I am not sure what to expect if foo::dosomething raises an exception.
>> Is code safe for exception being traversing through c code.
>
>
> As long as the C-code is being translated using a C++ compiler you're
> fine.
>
In that case, it's C++ code.

--
Ian Collins

peter koch

11/25/2008 6:56:00 PM

0

On 24 Nov., 23:22, Peter <ExcessPh...@gmail.com> wrote:
> On Nov 24, 11:07 am, abhijeet <abhi.10dul...@gmail.com> wrote:
>
> > Hi,
>
> > I was looking thru code in my organisation. same dll is sharingcode is
> > mixing c++ code & c code, which is being again called by some other c+
> > + dll.
>
> There is no need to translate any code with a c-compiler.
> Ansi C code compiles with a C++-compiler.
> My advice is to get rid of C code in favor or exception-safe-C++ code.

While I agree with you that most valid C code very likely also either
is valid C++ code or trivially can be changed into legal C++ code, it
is not enough to also make it "real" C++ code. Most important in this
aspect is the lack of exception safety, and this alone should be
reason enough to refrain you from taking such a short-cut.

/Peter