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mathiasn
Guest
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 Posted: Wed May 17, 2006 3:21 pm Post subject: Rethrow from other place than catch-block |
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|
Hi,
Is it legal to rethrow an exception from a function called from the
catch block?
Is the following program legal C++?
#include <iostream>
using namespace std;
void ExceptionHandler(const char* context)
{
cout << "In ExceptionHandler(" << context << "):";
try // Setup a new try-block and rethrow the exception
{
throw;
}
catch (const int& e)
{
cout << "int = " << e << "\n";
}
catch (const char* e)
{
cout << "text = " << e << "\n";
}
catch (...)
{
cout << "UNKNOWN\n";
}
}
int _tmain(int argc, _TCHAR* argv[])
{
for (int i = 0; i < 5; ++i)
{
try
{
switch (i)
{
case 0: throw 42;
case 1: throw "Some text";
case 2: throw 12.4;
case 3: cout << "Still alive\n"; break;
case 4:
{
try
{
throw "Another text";
}
catch (...)
{
ExceptionHandler("Other context");
}
}
break;
}
}
catch (...) // Catch all exceptions here
{
ExceptionHandler("Inside for loop");
}
}
return 0;
}
This small testprogram compiles and runs as expected with Visual C++
2005. But in our bigger system we are expecting that code like this is
causing problems.
Best regards
Mathias
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red floyd
Guest
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| Posted: Wed May 17, 2006 10:21 pm Post subject: Re: Rethrow from other place than catch-block |
|
|
mathiasn wrote:
| Quote: | Hi,
Is it legal to rethrow an exception from a function called from the
catch block?
Is the following program legal C++?
|
Technically, no, because _TCHAR is undefined and there is no main.
That said, assuming MS usage, yes, it appears to be legal. 15.1/6-8.
| Quote: | #include <iostream
using namespace std;
void ExceptionHandler(const char* context)
{
cout << "In ExceptionHandler(" << context << "):";
try // Setup a new try-block and rethrow the exception
{
throw;
}
catch (const int& e)
{
cout << "int = " << e << "\n";
}
catch (const char* e)
{
cout << "text = " << e << "\n";
}
catch (...)
{
cout << "UNKNOWN\n";
}
}
int _tmain(int argc, _TCHAR* argv[])
{
for (int i = 0; i < 5; ++i)
{
try
{
switch (i)
{
case 0: throw 42;
case 1: throw "Some text";
case 2: throw 12.4;
case 3: cout << "Still alive\n"; break;
case 4:
{
try
{
throw "Another text";
}
catch (...)
{
ExceptionHandler("Other context");
}
}
break;
}
}
catch (...) // Catch all exceptions here
{
ExceptionHandler("Inside for loop");
}
}
return 0;
}
|
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Alf P. Steinbach
Guest
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| Posted: Wed May 17, 2006 10:21 pm Post subject: Re: Rethrow from other place than catch-block |
|
|
* mathiasn:
| Quote: |
Is it legal to rethrow an exception from a function called from the
catch block?
|
Yes, but it's not supported by some older compilers, in particular, it's
not supported by Visual C++ 6.0 and earlier (a compiler bug wrt.
destructor calls).
| Quote: | Is the following program legal C++?
|
No, because
1) it's lacking
#include <ostream>
;-)
2) it's using a non-standard startup function '_tmain'; of course
that's meant to be defined as a preprocessor symbol 'main' when
building the program, but it won't compile without such def.
| Quote: | #include <iostream
using namespace std;
void ExceptionHandler(const char* context)
{
cout << "In ExceptionHandler(" << context << "):";
try // Setup a new try-block and rethrow the exception
{
throw;
}
catch (const int& e)
{
cout << "int = " << e << "\n";
}
catch (const char* e)
{
cout << "text = " << e << "\n";
}
catch (...)
{
cout << "UNKNOWN\n";
}
}
int _tmain(int argc, _TCHAR* argv[])
{
for (int i = 0; i < 5; ++i)
{
try
{
switch (i)
{
case 0: throw 42;
case 1: throw "Some text";
case 2: throw 12.4;
case 3: cout << "Still alive\n"; break;
case 4:
{
try
{
throw "Another text";
}
catch (...)
{
ExceptionHandler("Other context");
}
}
break;
}
}
catch (...) // Catch all exceptions here
{
ExceptionHandler("Inside for loop");
}
}
return 0;
}
This small testprogram compiles and runs as expected with Visual C++
2005. But in our bigger system we are expecting that code like this is
causing problems.
|
I would also expect that, because the function breaks a golden rule of
design: separation of concerns.
Let the function return the information needed to process the exception,
e.g., some descriptive text, or let it rethrow the exception with some
project-standard exception type.
Don't let it process the exception: it doesn't know what's appropriate.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
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Sergey P. Derevyago
Guest
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| Posted: Wed May 17, 2006 10:21 pm Post subject: Re: Rethrow from other place than catch-block |
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mathiasn wrote:
| Quote: | Is it legal to rethrow an exception from a function called from the
catch block?
It must be legal. |
In particular, ARM contains the following example:
void pass_through() { throw; }
void g()
{
PFV old = set_unexpected(&pass_through);
try { f(); }
catch (X) { }
catch (Y) { }
catch (...) { }
set_unexpected(old);
}
And my Russian "Interfaces and Messages" tutorial uses this technique to
implement common newCException() handler:
void f()
{
try { g(); }
catch (...) {
throw newCException(_FLINE_, "Problems in f()", toCException(_FLINE_));
}
}
sh_ptr<CException> toCException(const CException::FileLine& location)
{
#ifndef DERS_RETHROW_BUG // normal version
try { throw; }
catch (sh_ptr<CException> ce) {
return ce;
}
catch (const exception& e) {
return newSTDExternalCException(location, e.what(), typeid(e).name());
}
catch (...) {
return newUnknownExternalCException(location, "Unknown exception",
"unknown");
}
#else // version for broken compilers
if (CException::current.refs()>1 && CException::current.get())
return CException::current;
return newUnknownExternalCException(location, "Unknown exception",
"unknown");
#endif
}
You can download the source code http://ders.angen.net/cpp3/intmsg/code.zip
and run ceexample.cpp
| Quote: | This small testprogram compiles and runs as expected with Visual C++
2005. But in our bigger system we are expecting that code like this is
causing problems.
Yes, it does. |
Unfortunately, I have to define DERS_RETHROW_BUG macro if the nested
rethrowing isn't supported by a particular compiler.
--
With all respect, Sergey. http://ders.angen.net/
mailto : ders at skeptik.net
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David Abrahams
Guest
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| Posted: Wed May 17, 2006 10:21 pm Post subject: Re: Rethrow from other place than catch-block |
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|
"mathiasn" <mathias.nord (AT) gmail (DOT) com> writes:
| Quote: | Hi,
Is it legal to rethrow an exception from a function called from the
catch block?
Is the following program legal C++?
|
Yes and yes.
--
Dave Abrahams
Boost Consulting
www.boost-consulting.com
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Andrew Koenig
Guest
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| Posted: Wed May 17, 2006 10:21 pm Post subject: Re: Rethrow from other place than catch-block |
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|
"mathiasn" <mathias.nord (AT) gmail (DOT) com> wrote in message
news:1147857637.106720.258710 (AT) j33g2000cwa (DOT) googlegroups.com...
| Quote: | Is it legal to rethrow an exception from a function called from the
catch block?
|
Yes.
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Hyman Rosen
Guest
|
| Posted: Wed May 17, 2006 10:21 pm Post subject: Re: Rethrow from other place than catch-block |
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|
mathiasn wrote:
| Quote: | Is it legal to rethrow an exception from a function called from the
catch block?
|
Yes, and it's useful for consolidating repetitive
handler blocks as your code demonstrates.
For a long time, Visual C++ would crash when you
did this, so many people don't use this construct.
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