Re: [Boost-users] How to store on exception object ?

31 Aug 2010


      The code below compiles on VS2010. 
Interestingly, operator != is not defined for std::exception_ptr.
=========================================================================
#include <cassert>
#include <exception>

std::exception_ptr g_ex;

void callback_cpp_impl(); // may throw
void call_C( void (*callback)() ) {}

void new_callback()
{
  try
  {
     callback_cpp_impl(); // may throw
  }
  catch(...)
  {
     assert(g_ex==nullptr);
     g_ex = std::current_exception();
  }
}
void foo()
{
  try
  {
    g_ex = nullptr;
    call_C(&new_callback);
    if( !(nullptr==g_ex) )
      std::rethrow_exception(g_ex);
  }
  catch(...) // normal catch as if the exception is thrown locally.
  {
  }
}


--------------------------------------------------
From: "Timothy Madden" 
Sent: Tuesday, August 31, 2010 1:05 PM
To: 
Subject: Re: [Boost-users] How to store on exception object ?
...
On 8/31/2010 7:01 PM, Binglong Xie wrote:
...
Does code below work correctly? (C++0x fashion)
=================================================================
My project uses Visual Studio 2008  and these C++0x functions do not 
work. Nice to see that they are about the enter the standard, though :)
And also, Visual Studio 2010 looks like it has these.
...
std::exception_ptr g_ex; //global variable is no good, may be wrapped
into callback params.
void my_callback()
{
try
{
callback_cpp_impl(); // may throw
}
catch(...)
{
assert(g_ex==nullptr);
g_ex = std::current_exception();
}
}
void foo()
{
try
{
g_ex = nullptr;
call_C(&my_callback);
if( g_ex!=nullptr )
std::rethrow_exception(g_ex);
}
catch... // normal catch as if the exception is thrown locally.
}
--------------------------------------------------
From: "Steven Watanabe" 
Sent: Tuesday, August 31, 2010 11:04 AM
To: 
Subject: Re: [Boost-users] How to store on exception object ?
...
AMDG
Timothy Madden wrote:
...
In a callback function I need to store and save an exception object
for until the callback is finished and the control is returned to my
application code. The callback is invoked by the C language code in
minizip library from zlib-1.2.3 contrib directory, and I need to
throw the exception when control returns to my application invoking
minizip functions.
This is true for any exception that might get thrown and caught in my
callback, so I would like to do that for any exception type.
However how can I store a thrown object for later re-throw without
the actual exception type ? Is there a way to do that ?
I think this is what boost::exception_ptr is for.
http://www.boost.org/libs/exception/doc/exception_ptr.html
In Christ,
Steven Watanabe
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