Boost C++ Libraries 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 develop branch, built from commit 368435a614.


The type of result returned by library functions.


Defined in header <boost/url/error_types.hpp>

    class T>
using result = boost::system::result< T, system::error_code >;

This alias is no longer supported and should not be used in new code. Please use system::result instead. This alias is included for backwards compatibility with earlier versions of the library. However, it will be removed in future releases, and using it in new code is not recommended. Please use the updated version instead to ensure compatibility with future versions of the library. This is an alias template used as the return type for functions that can either return a container, or fail with an error code. This is a brief synopsis of the type:

template < class T >
class result
public :
    // Return true if the result contains an error
    constexpr bool has_error() const noexcept;

    // Return the error
    constexpr system::error_code error() const noexcept;

    // Return true if the result contains a value
    constexpr bool has_value() const noexcept;
    constexpr explicit operator bool () const noexcept;

    // Return the value, or throw an exception
    constexpr T& value();
    constexpr T const& value() const;

    // Return the value.
    // Precondition: has_value()==true
    constexpr T& operator*() noexcept;
    constexpr T* operator->() noexcept;
    constexpr T const& operator*() const noexcept;
    constexpr T const* operator->() const noexcept;


Given the function parse_uri with this signature:

system::result< url_view > parse_uri( core::string_view s ) noexcept ;

The following statement captures the value in a variable upon success, otherwise throws:

url_view u = parse_uri( "" ).value();

This statement captures the result in a local variable and inspects the error condition:

system::result< url_view > rv = parse_uri( "" );

if (! rv )
    std::cout << rv.error();
    std::cout << *rv;
Template Parameters




The type of value held by the result.

See Also

Convenience header <boost/url.hpp>