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C++ Library containing a lot of needful things: Stack Trace, Command Line Parser, Resource Handling, Configuration Files, Unix Command Execution, Directories, Regular Expressions, Tokenizer, Function Trace, Standard Extensions.
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mrw-cxx/src/mrw/exception.hxx

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/** @file
$Id$
$Date$
$Author$
@copy © Marc Wäckerlin
@license LGPL, see file <a href="license.html">COPYING</a>
$Log$
Revision 1.12 2005/11/29 12:39:42 marc
make it compilable with gcc 4.0.2 and newer doxygen
Revision 1.11 2005/03/14 16:25:23 marc
changed size of dot image so that it fits an A4
Revision 1.10 2005/02/08 12:34:14 marc
added errno / unix_error
Revision 1.9 2005/01/28 12:18:37 marc
workaround for doxygen warning (doxygen misinterpreted class forward declaration)
Revision 1.8 2005/01/28 12:13:11 marc
interference between group name StackTrace and class name StackTrace
Revision 1.7 2005/01/28 12:13:11 marc
interference between group name StackTrace and class name StackTrace
Revision 1.6 2005/01/28 07:51:24 marc
improved and corrected trace formatting
Revision 1.5 2004/10/07 09:25:34 marc
new group for suggestions
new inheritance
Revision 1.4 2004/08/28 16:21:25 marc
mrw-c++-0.92 (mrw)
- new file: version.cxx
- new file header for all sources
- work around warning in mrw::auto<T>
- possibility to compile without log4cxx
- work around bugs in demangle.h and libiberty.h
- corrections in documentation
- added simple tracing mechanism
- more warnings
- small corrections in Auto<>::Free and a new test for it
- possibility to compile without stack trace
*/
#ifndef __MRW_EXCEPTION_HPP__
#define __MRW_EXCEPTION_HPP__
#include <exception>
#include <stdexcept>
#include <typeinfo>
#include <string>
namespace mrw {class StackTrace;} // work around Doxygen warning
namespace mrw {
/** @addtogroup grpStackTrace
@section exc Exception Handling with Stack Trace
One of the main reasons for the mrw::StackTrace class is, to be
able to store a trace where an exception is thrown. This trace
is then stored as exception information, but not yet evaluated,
symbols are calculated only if necessary, upon request. So the
exception is still relatively cheap.
There is a class named mrw::exception that derieves from and
behaves as @c std::exception, but it stores a mrw::StackTrace on
construction and offers a method @c mrw::exception::stacktrace()
that returns a well formatted stack trace of the point, where
the exception was created.
@subsection excprob Common Problems with Exception Handling
Exceptions are very handy: When you have a problem, you throw an
exception and when you call a method and reach the next line,
everything was fine. You don't have to care about error handling
unless you are able to handle it. Otherwise you simply let pass
any exception up in the stack.
The big disadvantage is, when you catch an exception, you don't
know where it was thrown. That's the stack trace for. Another
problem is, the exception specification problem: When you don't
write exception specifications, you don't know what a specific
method throws. If you do write exception specifications, they
are not checked at compile time, but enforced at run time. If a
wrong exception is thrown, the program stops, calls an
unexpected handler that by default aborts the program. Since the
unexpected handler must not return, the problem cannot be
recovered from. But the unexpected handler can rethrow and catch
the bad exception and it is allowed to throw a new
exception. This is what my suggested exception handling concept
makes use of.
*/
//@{
/** @example exceptionhandling.cxx
It is possible to recover from an unexpected exception! A stack
trace helps you to find the source of a problem, here function
@c fn2() in file @c /privat/home/marc/pro/mrw-c++/mrw/test.cxx
on line @c 25. This example produces the following output:
@verbatim
call fn0
enter fn0
enter fn1
enter fn2
UNEXPECTED:N3mrw9exceptionE
---------------------------Stack:
[ 0x8048e11] _start ../sysdeps/i386/elf/start.S:105
[0x4016e92b] __libc_start_main ????:0
[ 0x8049392] main /.../mrw-c++/mrw/examples/exceptionhandling.cxx:50
[ 0x8049265] fn0() /.../mrw-c++/mrw/examples/exceptionhandling.cxx:38
[ 0x80491e9] fn1() /.../mrw-c++/mrw/examples/exceptionhandling.cxx:32
[ 0x8049183] fn2() /.../mrw-c++/mrw/examples/exceptionhandling.cxx:25
[0x400494a4] mrw::exception::exception() ????:0
[0x4005ace5] mrw::StackTrace::StackTrace() ????:0
---------------------------------
EXCEPTION caught in fn0:St13bad_exception
leave fn0
call of fn0 successful
@endverbatim
The unexpected handler is implemented ready to use in @ref
AutoTrace "a separate library".
Please note, that without the exception concept and without the
unexpected handler, the program would abort in function fn2 on
line 25. The output was produced by the following code:
*/ /* here follows the example code... */
/** @defgroup exceptions Exceptions with Stack Trace
The following diagram shows the inheritance of the MRW exception
classes and how they are related to the C++ standard
exceptions. @c mrw::exception inherits @c std::exception, then a
inheritance corresponding to the standard is implemented below
@c mrw::exception. To prevent diamond-shaped inheritance, the MRW
exceptions below the @c mrw::exception base class do not inherit
from their corresponding standard exception.
The exception classes are meant as a replacement to the standard
exceptions that provide stack trace information. I suggest
exception handling according to @ref excsug.
@dot
digraph ExceptionInheritance {
graph [rankdir="LR", size="7,8"];
node [shape=box, fontname=Helvetica, fontsize=8];
edge [dir=back, headport=w, tailport=e, arrowtail=empty];
std_exception [label="std::exception"];
std_bad_alloc [label="std::bad_alloc"];
std_bad_cast [label="std::bad_cast"];
std_logic_error [label="std::logic_error"];
std_domain_error [label="std::domain_error"];
std_invalid_argument [label="std::invalid_argument"];
std_length_error [label="std::length_error"];
std_out_of_range [label="std::out_of_range"];
std_runtime_error [label="std::runtime_error"];
std_overflow_error [label="std::overflow_error"];
std_range_error [label="std::range_error"];
std_underflow_error [label="std::underflow_error"];
std_bad_exception [label="std::bad_exception"];
std_bad_typeid [label="std::bad_typeid"];
mrw_exception [label="mrw::exception" URL="\ref mrw::exception"];
mrw_bad_alloc [label="mrw::bad_alloc" URL="\ref mrw::bad_alloc"];
mrw_bad_cast [label="mrw::bad_cast" URL="\ref mrw::bad_cast"];
mrw_logic_error [label="mrw::logic_error" URL="\ref mrw::logic_error"];
mrw_domain_error [label="mrw::domain_error" URL="\ref mrw::domain_error"];
mrw_invalid_argument [label="mrw::invalid_argument" URL="\ref mrw::invalid_argument"];
mrw_length_error [label="mrw::length_error" URL="\ref mrw::length_error"];
mrw_out_of_range [label="mrw::out_of_range" URL="\ref mrw::out_of_range"];
mrw_runtime_error [label="mrw::runtime_error" URL="\ref mrw::runtime_error"];
mrw_overflow_error [label="mrw::overflow_error" URL="\ref mrw::overflow_error"];
mrw_range_error [label="mrw::range_error" URL="\ref mrw::range_error"];
mrw_underflow_error [label="mrw::underflow_error" URL="\ref mrw::underflow_error"];
mrw_unix_error [label="mrw::unix_error" URL="\ref mrw::unix_error"];
mrw_bad_exception [label="mrw::bad_exception" URL="\ref mrw::bad_exception"];
mrw_bad_typeid [label="mrw::bad_typeid" URL="\ref mrw::bad_typeid"];
{rank=same; std_exception; mrw_exception;}
{rank=same; std_bad_alloc; mrw_bad_alloc;}
{rank=same; std_bad_cast; mrw_bad_cast;}
{rank=same; std_logic_error; mrw_logic_error;}
{rank=same; std_domain_error; mrw_domain_error;}
{rank=same; std_invalid_argument; mrw_invalid_argument;}
{rank=same; std_length_error; mrw_length_error;}
{rank=same; std_out_of_range; mrw_out_of_range;}
{rank=same; std_runtime_error; mrw_runtime_error;}
{rank=same; std_overflow_error; mrw_overflow_error;}
{rank=same; std_range_error; mrw_range_error;}
{rank=same; std_underflow_error; mrw_underflow_error;}
{rank=same; std_bad_exception; mrw_bad_exception;}
{rank=same; std_bad_typeid; mrw_bad_typeid;}
mrw_exception -> mrw_bad_alloc;
mrw_exception -> mrw_bad_cast;
mrw_exception -> mrw_logic_error;
mrw_logic_error -> mrw_domain_error;
mrw_logic_error -> mrw_invalid_argument;
mrw_logic_error -> mrw_length_error;
mrw_logic_error -> mrw_out_of_range;
mrw_exception -> mrw_runtime_error;
mrw_runtime_error -> mrw_overflow_error;
mrw_runtime_error -> mrw_range_error;
mrw_runtime_error -> mrw_underflow_error;
mrw_runtime_error -> mrw_unix_error;
mrw_exception -> mrw_bad_exception;
mrw_exception -> mrw_bad_typeid;
std_exception -> std_bad_alloc;
std_exception -> std_bad_cast;
std_exception -> std_logic_error;
std_logic_error -> std_domain_error;
std_logic_error -> std_invalid_argument;
std_logic_error -> std_length_error;
std_logic_error -> std_out_of_range;
std_exception -> std_runtime_error;
std_runtime_error -> std_overflow_error;
std_runtime_error -> std_range_error;
std_runtime_error -> std_underflow_error;
std_exception -> std_bad_exception;
std_exception -> std_bad_typeid;
std_exception -> mrw_exception;
}
@enddot
*/
//@{
/** @brief replacement for @c std::exception, that collects a stack trace
@pre \#include <mrw/exception.hxx>
This exception class behaves exactely like @c std::exception,
but it collects a stack trace in the constructor and offers a
method to return the formatted stack trace for logging.
It is recommended, to inherit all the exceptions you ever throw
from this class. This way you can always access the stack trace
if you run into troubles. It is fursther recommended, to write a
unexpected handler, that rethrows, catches this exception, then
throws a @c std::bad_exception to try to continue. This is the
reason, why all the exception specifications in the MRW C++
Library declar @c instead of @c
noexcept, when they throw nothing.
@code
namespace myProject {
void unexpectedHandler() {
try {
throw;
} catch (mrw::exception& x) {
// trace x.stacktrace() and x.what()
} catch (std::exception& x) {
// trace x.what()
} catch (...) {
// trace unknown unexpected
}
throw std::bad_exception(); // try to recover
}
}
int main() {
std::set_unexpected(&myProject::unexpectedHandler);
...
}
@endcode
*/
class exception: public std::exception {
public:
exception() ;
virtual ~exception() noexcept;
virtual const char* what() const noexcept {
return std::exception::what();
}
const std::string& stacktrace() const ;
private:
StackTrace* _stacktrace;
};
/// Replacement for @c std::bad_alloc, but with stack trace
class bad_alloc: public mrw::exception {
public:
~bad_alloc() noexcept {}
virtual const char* what() const noexcept {
return "mrw::bad_alloc";
}
};
/// Replacement for @c std::bad_cast, but with stack trace
class bad_cast: public mrw::exception {
public:
~bad_cast() noexcept {}
virtual const char* what() const noexcept {
return "mrw::bad_cast";
}
};
/// Replacement for @c std::bad_exception, but with stack trace
class bad_exception: public mrw::exception {
public:
~bad_exception() noexcept {}
virtual const char* what() const noexcept {
return "mrw::bad_exception";
}
};
/// Replacement for @c std::bad_typeid, but with stack trace
class bad_typeid: public mrw::exception {
public:
~bad_typeid() noexcept {}
virtual const char* what() const noexcept {
return "mrw::bad_typeid";
}
};
/// Replacement for @c std::logic_error, but with stack trace
class logic_error: public mrw::exception {
public:
~logic_error() noexcept {}
logic_error(const std::string& arg) noexcept: _what(arg) {}
virtual const char* what() const noexcept {
return _what.c_str();
}
private:
std::string _what;
};
/// Replacement for @c std::domain_error, but with stack trace
class domain_error: public mrw::logic_error {
public:
~domain_error() noexcept {}
domain_error(const std::string& arg) noexcept: mrw::logic_error(arg) {}
virtual const char* what() const noexcept {
return mrw::logic_error::what();
}
};
/// Replacement for @c std::invalid_argument, but with stack trace
class invalid_argument: public mrw::logic_error {
public:
~invalid_argument() noexcept {}
invalid_argument(const std::string& arg) noexcept: mrw::logic_error(arg) {}
virtual const char* what() const noexcept {
return mrw::logic_error::what();
}
};
/// Replacement for @c std::length_error, but with stack trace
class length_error: public mrw::logic_error {
public:
~length_error() noexcept {}
length_error(const std::string& arg) noexcept: mrw::logic_error(arg) {}
virtual const char* what() const noexcept {
return mrw::logic_error::what();
}
};
/// Replacement for @c std::out_of_range, but with stack trace
class out_of_range: public mrw::logic_error {
public:
~out_of_range() noexcept {}
out_of_range(const std::string& arg) noexcept: mrw::logic_error(arg) {}
virtual const char* what() const noexcept {
return mrw::logic_error::what();
}
};
/// Replacement for @c std::runtime_error, but with stack trace
class runtime_error: public mrw::exception {
public:
~runtime_error() noexcept {}
runtime_error(const std::string& arg) noexcept: _what(arg) {}
virtual const char* what() const noexcept {
return _what.c_str();
}
private:
std::string _what;
};
/// Replacement for @c std::overflow_error, but with stack trace
class overflow_error: public mrw::runtime_error {
public:
~overflow_error() noexcept {}
overflow_error(const std::string& arg) noexcept: mrw::runtime_error(arg) {}
virtual const char* what() const noexcept {
return mrw::runtime_error::what();
}
};
/// Replacement for @c std::range_error, but with stack trace
class range_error: public mrw::runtime_error {
public:
~range_error() noexcept {}
range_error(const std::string& arg) noexcept: mrw::runtime_error(arg) {}
virtual const char* what() const noexcept {
return mrw::runtime_error::what();
}
};
/// Replacement for @c std::underflow_error, but with stack trace
class underflow_error: public mrw::runtime_error {
public:
~underflow_error() noexcept {}
underflow_error(const std::string& arg) noexcept: mrw::runtime_error(arg) {}
virtual const char* what() const noexcept {
return mrw::runtime_error::what();
}
};
//@}
/** @defgroup excsug Suggested Exception Handling Rules
-# derieve all your exceptions from mrw::exception
-# write exception specifications as follows: @n
(this specification is "binary", it only declares whether an exception
is thrown or not, but it does not specify which exact exception can
be thrown)
- if no exception is thrown, specify @c noexcept
- if any exception is thrown specify nothing
- only declare @c noexcept if you are 100% sure, that it is absolutely
impossible that this method ever throws an exception, that means
this method calls no other function or method (not even from a
system library) that does not declare @c noexcept
-# document the exact exception thrown with Doxygen's @c \@throw tag
-# add a terminate handler to catc
-# in @c main catch everything and trace errors:
(or link to a @ref AutoTrace "library"):
@code
#include <exception>
...
set_terminate([]{
try {
auto p = std::current_exception();
if (p) std::rethrow_exception (p);
// trace other problem
} catch (mrw::exception& x) {
// trace x.stacktrace() and x.what()
} catch (std::exception& x) {
// trace x.what()
} catch (...) {
// trace unknown unexpected
}
}
@endcode
What happens:
- If you throw an exception in a method that declares not to
throw an exception, the terminate handler is called.
- It writes a stack trace for you to be able to find your bug.
- Then it throws a @c std::bad_exception, which is allowed to pass.
- Your program does not abort, but continues running.
- If higher in the stack you catch the exception, you may be
able to recover.
- If you throw an exception where you are allowed to, you only need to
catch mrw::exception and you can access @c what() and @c stacktrace().
For a proof of concept refer to
@ref exceptionhandling.cxx "the example exceptionhandling.cxx".
The unexpected handler is implemented ready to use in @ref
AutoTrace "a separate library".
*/
//@}
}
#endif