boost/exception/info.hpp
diagnostic_information
+error_info::error_info
+error_info::value
+error_info::value_type
exception
exception/operator<<
get_error_info
diff --git a/doc/error_info_error_info.html b/doc/error_info_error_info.html new file mode 100644 index 0000000..e576e1d --- /dev/null +++ b/doc/error_info_error_info.html @@ -0,0 +1,52 @@ + + + + +
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diff --git a/doc/error_info_value.html b/doc/error_info_value.html
new file mode 100644
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+Boost Exception
+error_info::error_info
+#include <boost/exception/info.hpp>
+error_info( value_type const & v );
+Effects:
+Stores a copy of v in the error_info object.
+Throws:
+Any exception emitted by v's copy constructor.
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+Copyright (c) 2006-2008 by Emil Dotchevski and Reverge Studios, Inc.
+Distributed under the Boost Software License, Version 1.0.
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diff --git a/doc/error_info_value_type.html b/doc/error_info_value_type.html
new file mode 100644
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+Boost Exception
+error_info::value
+#include <boost/exception/info.hpp>
+value_type const & value() const;
+Description:
+Returns a const reference to the copy of the value passed to error_info's constructor stored in the error_info object.
+Throws:
+Nothing.
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+Copyright (c) 2006-2008 by Emil Dotchevski and Reverge Studios, Inc.
+Distributed under the Boost Software License, Version 1.0.
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diff --git a/doc/exception_diagnostic_information_hpp.html b/doc/exception_diagnostic_information_hpp.html
index 8214df6..31af0eb 100644
--- a/doc/exception_diagnostic_information_hpp.html
+++ b/doc/exception_diagnostic_information_hpp.html
@@ -28,7 +28,7 @@ namespace
boost
{
class exception;
- std::string diagnostic_information( boost::exception const & x );
+ std::string diagnostic_information( boost::exception const & );
}
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+Boost Exception
+error_info::value_type
+#include <boost/exception/info.hpp>
+typedef T value_type;
+Definition:
+The expression error_info<Tag,T>::value_type evaluates to T.
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+Copyright (c) 2006-2008 by Emil Dotchevski and Reverge Studios, Inc.
+Distributed under the Boost Software License, Version 1.0.
+
See Also:
diff --git a/doc/exception_error_info_hpp.html b/doc/exception_error_info_hpp.html index d4a1238..1e6c045 100644 --- a/doc/exception_error_info_hpp.html +++ b/doc/exception_error_info_hpp.html @@ -35,9 +35,10 @@ boost { public: - typedef T value_type; + typedef T value_type; - error_info( value_type const & ); + error_info( value_type const & v ); + value_type const & value() const; }; template <class E, class Tag, class T> @@ -48,6 +49,9 @@ boostThe get_error_info function template is instantiated with the typedef from (1), and is passed an exception object of a polymorphic type. If the exception object contains the requested value, the returned shared_ptr will point to it; otherwise an empty shared_ptr is returned.
Adding of Arbitrary Data to Active Exception Objects
Sometimes the throw site does not have all the information that is needed at the catch site to make sense of what went wrong. Here is an example:
-#include <stdio.h>
-#include <string>
-
-class
-file_read_error
- {
- public:
-
- explicit
- file_read_error( std::string const & fn ):
- fn_(fn)
- {
- };
-
- std::string const &
- file_name() const
- {
- return fn_;
- }
-
- private:
-
- std::string fn_;
- };
-
-void
+Sometimes the throw site does not have all the information that is needed at the catch site to make sense of what went wrong. Let's say we have an exception type file_read_error, which takes a file name in its constructor. Consider the following function:
+void
file_read( FILE * f, void * buffer, size_t size )
{
if( size!=fread(buffer,1,size,f) )
- throw file_read_error("????");
+ throw file_read_error(????);
}
-We have defined an exception class file_read_error which can store a file name, so that when we catch a file_read_error object, we know which file the failure is related to. However, the file_read function does not have the file name at the time of the throw; all it has is a FILE handle.
-One possible solution is to not use FILE handles directly. We could have our own class file which stores both a FILE handle and a file name, and pass that to file_read. However, this could be problematic if we communicate with 3rd party code that does not use our class file (probably because they have their own similar class.)
-A better solution is to make class file_read_error derive (possibly indirectly) from boost::exception, and free the file_read function from the burden of storing the file name in exceptions it throws:
+How can the file_read function pass a file name to the exception type constructor? All it has is a FILE handle.
+Using boost::exception allows us to free the file_read function from the burden of storing the file name in exceptions it throws:
#include <boost/exception.hpp>
#include <stdio.h>
#include <errno.h>
@@ -140,7 +114,6 @@ parse_file( char const * file_name )
}
}
The above function is (almost) exception-neutral -- if an exception is emitted by any function call within the try block, parse_file does not need to do any real work, but it intercepts any boost::exception object, stores the file name, and re-throws using a throw-expression with no operand (15.1.6). The rationale for catching any boost::exception object is that the file name is relevant to any failure that occurs in parse_file, even if the failure is unrelated to file I/O.
-As usual, the stored data can be retrieved using get_error_info.
Adding Grouped Data to Exceptions
The code snippet below demonstrates how boost::tuple can be used to bundle the name of the function that failed, together with the reported errno so that they can be added to exception objects more conveniently together: