Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for a snapshot of the master branch, built from commit 20a7dc9240.
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result_from_errno

Create result storing a portable error code.

Synopsis

Defined in header <boost/json/system_error.hpp>

template<
    class T>
result_for< T, value >::type
result_from_errno(
    int e,
    boost::source_location const* loc);
Description

This function constructs a result<T> that stores error_code with value() equal to e and category() equal to boost::system::generic_category().

The main use for this function is in implementation of functions returning result, without including boost/json/system_error.hpp or even <system_error>. In particular, it may be useful for customizations of try_value_to without creating a physical dependency on Boost.JSON. For example:

#include <cerrno>
#include <boost/assert/source_location.hpp>

namespace boost
{
namespace json
{

class value;

template<class T>
struct try_value_to_tag;

template<class T1, class T2>
struct result_for;

template <class T>
typename result_for<T, value>::type
result_from_errno(int e, boost::source_location const* loc) noexcept

}
}

namespace mine
{

class my_class;
...
template<class JsonValue>
boost::json::result_for<my_class, JsonValue>
tag_invoke(boost::json::try_value_to_tag<my_class>, const JsonValue& jv)
{
    BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
    if( !jv.is_null() )
        return boost::json::result_from_errno<my_class>(EINVAL, &loc);
    return my_class();
}

}
Exception Safety

Does not throw exceptions.

Template Parameters

Type

Description

T

The value type of returned result.

Parameters

Name

Description

e

The error value.

loc

The error location.

Return Value

error_code with value() equal to e and category() equal to boost::system::generic_category().

See Also

try_value_to_tag, try_value_to, result_for, boost::system::generic_category, boost::source_location.

Convenience header <boost/json.hpp>


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