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Boost Exception


#include <boost/exception/diagnostic_information.hpp> 
#include <boost/exception_ptr.hpp> 

    template <class E>
    std::string diagnostic_information( E const & e, bool verbose=true );
    std::string diagnostic_information( exception_ptr const & p, bool verbose=true );


A string value that contains varying amount of diagnostic information about the passed object:

  • If E can be statically converted to either boost::exception or to std::exception, dynamic_cast is used to access both the boost::exception and std::exception subobjects of e; otherwise, the boost::diagnostic_information template is not available.
  • The returned value contains the string representations of all error_info objects stored in the boost::exception subobject through operator<<.
  • In addition, if verbose is true, it contains other diagnostic information relevant to the exception, including the string returned by std::exception::what().

The string representation of each error_info object is deduced by an unqualified call to to_string(x), where x is of type error_info<Tag,T>, for which Boost Exception defines a generic overload. It converts x.value() to string, attempting to bind (at the time the error_info<Tag,T> template is instantiated) the following functions in order:

  1. Unqualified call to to_string(x.value()) (the return value is expected to be of type std::string.)
  2. Unqualified call to s << x.value(), where s is a std::ostringstream.

The first successfully bound function is used at the time diagnostic_information is called; if both overload resolutions are unsuccessful, the system is unable to convert the error_info object to string, and an unspecified stub string value is used without issuing a compile error.

The exception_ptr overload of diagnostic_information is equivalent to:

if( p )
        return current_exception_diagnostic_information(verbose);
else return <unspecified-string-value>;


this is a possible output from the diagnostic_information function, as used in libs/exception/example/example_io.cpp:

example_io.cpp(70): Throw in function class boost::shared_ptr<struct _iobuf> __cdecl my_fopen(const char *,const char *)
Dynamic exception type: class boost::exception_detail::clone_impl<struct fopen_error>
std::exception::what: example_io error
[struct boost::errinfo_api_function_ *] = fopen
[struct boost::errinfo_errno_ *] = 2, "No such file or directory"
[struct boost::errinfo_file_name_ *] = tmp1.txt
[struct boost::errinfo_file_open_mode_ *] = rb