+
+
+
+
+
Boost Exception
+
+
Abstract
+
The purpose of Boost Exception is to ease the design of exception class hierarchies and to help write exception handling and error reporting code.
+
It supports transporting of arbitrary data to the catch site, which is otherwise tricky due to the no-throw requirements (15.5.1) for exception classes. Data can be added to any exception object, either directly in the throw-expression (15.1), or at a later time as the exception object propagates up the call stack.
+
The ability to add data to exception objects after they have been passed to throw is important, because often some of the information needed to handle an exception is unavailable in the context where the failure is detected.
+
Boost Exception also supports cloning of exception objects, implemented non-intrusively and automatically by the boost::throw_exception() function.
+
Note:
+
Boost Exception was accepted as a Boost library on November 7, 2007; however it has not yet been part of an official Boost release.
+
Contents
+
+
Synopsis
+
#include <boost/exception.hpp>
+
namespace
+boost
+ {
+ class
+ exception
+ {
+ public:
+
+ virtual char const * what() const throw();
+
+ protected:
+
+ exception();
+ exception( exception const & x );
+ ~exception();
+
+ private:
+
+ ---unspecified---
+ };
+
+ template <class Tag,class T>
+ class
+ error_info
+ {
+ public:
+
+ typedef T value_type;
+
+ error_info( value_type const & );
+
+ private:
+
+ ---unspecified---
+ };
+
+ template <class E, class Tag1, class T1>
+ E const & operator<<( E const & x, error_info<Tag1,T1> const & v );
+
+ template <class E, class Tag1, class T1, ..., class TagN, class TN>
+ E const & operator<<( E const & x,
+ tuple<
+ error_info<Tag1,T1>,
+ ...,
+ error_info<TagN,TN> > const & v );
+
+ template <class ErrorInfo,class E>
+ shared_ptr<typename ErrorInfo::value_type const> get_error_info( E const & x );
+
+ template <class T>
+ ---unspecified--- enable_error_info( T const & x );
+
+ typedef error_info<struct tag_throw_function,char const *> throw_function;
+ typedef error_info<struct tag_throw_file,char const *> throw_file;
+ typedef error_info<struct tag_throw_line,int> throw_line;
+
+ #define BOOST_ERROR_INFO\
+ ::boost::throw_function(BOOST_CURRENT_FUNCTION) <<\
+ ::boost::throw_file(__FILE__) <<\
+ ::boost::throw_line((int)__LINE__)
+
+ typedef ---unspecified--- exception_ptr;
+
+ template <class T>
+ ---unspecified--- enable_exception_cloning( T const & e );
+
+ template <class T>
+ exception_ptr clone_exception( T const & e );
+ void rethrow_exception( exception_ptr const & ep );
+
+ class
+ unknown_exception:
+ public std::exception
+ public boost::exception
+ {
+ ---unspecified---
+ };
+
+#ifdef BOOST_NO_EXCEPTIONS
+ void throw_exception( std::exception const & e ); // user defined
+#else
+ template <class E>
+ void throw_exception( E const & e );
+#endif
+ }
+
exception
+
Class boost::exception is designed to be used as a universal base for user-defined exception types.
+
An object of any type deriving from boost::exception can store data of arbitrary types, using the error_info wrapper and operator<<().
+
To retrieve data from a boost::exception object, use the get_error_info() function template.
+
exception constructors
+
Effects:
+
- Default constructor: initializes an empty boost::exception object.
+- Copy constructor: initializes a boost::exception object which shares with x all data added through operator<<(), including data that is added at a future time.
+
+
Throws:
+
Nothing.
+
exception destructor
+
Effects:
+
Frees all resources associated with a boost::exception object.
+
Throws:
+
Nothing.
+
exception::what()
+
virtual char const * what() const throw();
+
Returns:
+
An string representation of all data stored in the boost::exception object by the operator<<() function. See "Tutorial: Logging of boost::exception Objects" for details.
+
Throws:
+
Nothing.
+
Note:
+
The return value remains valid until the exception object from which it is obtained is destroyed or modified.
+
Transporting of Arbitrary Data to the Catch Site
+
error_info
+
#include <boost/exception/info.hpp>
+
namespace
+boost
+ {
+ template <class Tag,class T>
+ class
+ error_info
+ {
+ public:
+
+ typedef T value_type;
+
+ error_info( value_type const & );
+
+ private:
+
+ ---unspecified---
+ };
+ }
+
Requirements:
+
T must have accessible copy constructor and must not be a reference.
+
Description:
+
This class template is used to associate a Tag type with a value type T. Objects of type error_info<Tag,T> can be passed to operator<<() to be stored in objects of type boost::exception.
+
Note:
+
The header <boost/exception/error_info.hpp> provides a declaration of the error_info template, which is sufficient for the purpose of typedefing an instance for specific Tag and T, like this:
+
#include <boost/exception/error_info.hpp>
+
+typedef boost::error_info<struct tag_errno,int> errno_info;
+
Of course, to actually add an errno_info object to exceptions using operator<<(), or to retrieve it using get_error_info(), you must first #include <boost/exception/info.hpp>.
+
operator<<()
+
#include <boost/exception/info.hpp>
#include <boost/exception/info_tuple.hpp>
+
namespace
+boost
+ {
+ template <class E, class Tag1, class T1>
+ E const & operator<<( E const & x, error_info<Tag1,T1> const & v );
+
+ template <class E, class Tag1, class T1, ..., class TagN, class TN>
+ E const & operator<<( E const & x,
+ tuple<
+ error_info<Tag1,T1>,
+ ...,
+ error_info<TagN,TN> > const & v );
+ }
+
Requirements:
+
E must be boost::exception, or a type that derives (indirectly) from boost::exception.
+
Effects:
+
- The first overload stores a copy of v into x. If x already contains data of type error_info<Tag1,T1>, that data is overwritten.
+- The boost::tuple overload is equivalent to x << v.get<0>() << ... << v.get<N>().
+
+
Returns:
+
x.
+
Throws:
+
std::bad_alloc, or any exception emitted by T1..TN copy constructor.
+
get_error_info()
+
Requirements:
+
The type of the x object must derive from boost::exception; ErrorInfo must be an instance of the error_info template.
+
Returns:
+
If x does not store an object of type ErrorInfo, returns an empty shared_ptr; otherwise returns pointer to the stored value. Use operator<<() to store values in exception objects.
+
Throws:
+
Nothing.
+
enable_error_info()
+
Requirements:
+
T must be a user-defined type with accessible no-throw copy constructor.
+
Returns:
+
An object of unspecified type with no-throw copy semantics, which derives publicly from both T, and class boost::exception. The T sub-object is initialized from x by the T copy constructor. If T already derives from boost::exception, then the type of the returned object does not derive boost::exception.
+
Throws:
+
Nothing.
+
BOOST_ERROR_INFO
+
#include <boost/exception/info.hpp>
+
namespace
+boost
+ {
+ typedef error_info<struct tag_throw_function,char const *> throw_function;
+ typedef error_info<struct tag_throw_file,char const *> throw_file;
+ typedef error_info<struct tag_throw_line,int> throw_line;
+
+ #define BOOST_ERROR_INFO\
+ ::boost::throw_function(BOOST_CURRENT_FUNCTION) <<\
+ ::boost::throw_file(__FILE__) <<\
+ ::boost::throw_line((int)__LINE__)
+ }
+
This macro is designed to be used with operator<<() when throwing a boost::exception, to store information about the location of the throw statement. It can be chained with other error_infos in a single throw expression.
+
Transporting of Exceptions between Threads
+
exception_ptr
+
The exception_ptr type can be used to refer to a copy of a boost::exception object. It is Default Constructible, Copy Constructible, Assignable and Equality Comparable; exception_ptr's operations do not throw.
+
Two instances of exception_ptr are equivalent and compare equal if and only if they refer to the same exception.
+
The default constructor of exception_ptr produces the null value of the type. The null value is equivalent only to itself.
+
enable_exception_cloning()
+
Requirements:
+
T must have an accessible no-throw copy constructor
+
Returns:
+
An object of unspecified type which derives publicly from T. That is, the returned object can be intercepted by a catch(T &).
+
Description:
+
This function is designed to be used directly in a throw-expression to enable the cloning support in Boost Exception. For example:
+
class
+my_exception:
+ public std::exception
+ {
+ };
+
+....
+throw boost::enable_exception_cloning(my_exception());
+
Unless enable_exception_cloning() is called at the time an exception object is used in a throw-expression, any attempt to copy it using clone_exception() returns an exception_ptr which refers to an instance of unknown_exception.
+
Note:
+
Instead of using the throw keyword directly, it is preferable to call boost::throw_exception(). This is guaranteed to throw an exception that derives from boost::exception and supports cloning.
+
clone_exception()
+
Requirements:
+
T must be polymorphic.
+
Returns:
+
+
Note:
+
It is unspecified whether the return values of two successive calls to clone_exception() refer to the same exception object.
+
rethrow_exception()
+
Precondition:
+
ep shall not be null.
+
Throws:
+
The exception to which ep refers.
+
Throwing Exceptions
+
throw_exception()
+
Effects:
+
- If BOOST_NO_EXCEPTIONS is not defined, boost::throw_exception(e) is equivalent to throw boost::enable_exception_cloning(boost::enable_error_info(e)), unless BOOST_EXCEPTION_DISABLE is defined, in which case boost::throw_exception(e) is equivalent to throw e;
+- If BOOST_NO_EXCEPTIONS is defined, the function is left undefined, and the user is expected to supply an appropriate definition. Callers of throw_exception are allowed to assume that the function never returns; therefore, if the user-defined throw_exception returns, the behavior is undefined.
+
+
+
+
+Copyright (c) 2006-2008 by Emil Dotchevski and Reverge Studios, Inc.