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//#define XERR
#include "category.ih"
//equiv
bool Category::equivalent(std::error_code const &ec, int condNr)
const noexcept
{
if (*this != ec.category())
return false;
if (ec.value() == 0) // no error in ec?
return condNr == 0; // then condNr must
// also be 0
auto iter = s_map.find(as<CatErr>(ec.value())); // info associated
// with ec's CatErr
return iter == s_map.end() ?
false // not found or
: // compare Cond values
iter->second.cond == as<Cond>(condNr);
}
//=
/*************************************************************************
The error_category::equivalent() virtual function is used to determine
equivalence between error codes and conditions. In fact, there are two
overloads of the error_category::equivalent() function.
The first overload:
bool equivalent(error_code const &code, int condition) const;
---------------------- ---------------
arbitrary error error condition
code in the current
cat
defines equivalence between error_conditions in the current category with
error_codes from any category.
The second:
bool equivalent(int code, error_condition const &condition) const;
--------- ---------------
error code arbitrary error
in the current condition
cat.
is used to establish equivalence between error_codes
in the current category with arbitrary error_conditions.
Since you are creating custom error conditions, it is the first overload that
you must override. Defining equivalence is simple: return true if you want an
error_code to be equivalent to your condition, otherwise return false.
If your intent is to abstract OS-specific errors, you might implement
error_category::equivalent() like this:
(api_category_impl::)
bool equivalent(std::error_code const &code, int condition) const
{
switch (condition)
{
case api_error::name_not_found:
return code == std::error_code(system_category());
default:
return false;
}
}
bool equivalent(std::error_code const &code, int condition) const
{
switch (condition) // available condition
{
// map the error code enum values in the current class
// on the conditions used in the current class and
// verify that the error code values are equal to
// the values of error_code code:
case low_system_resources: // the error condition
return code == not_enough_memory
|| code == resource_unavailable_try_again
|| code == too_many_files_open
|| code == too_many_files_open_in_system;
...
case api_error::no_such_entry:
return code == std::errc::no_such_file_or_directory;
default:
return false;
}
}
******************/
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