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- <body class="article toc2 toc-left">
- <div id="header">
- <h1>Boost.System: Extensible Error Reporting</h1>
- <div class="details">
- <span id="author" class="author">Beman Dawes, Christopher Kohlhoff, Peter Dimov</span><br>
- </div>
- <div id="toc" class="toc2">
- <div id="toctitle">Table of Contents</div>
- <ul class="sectlevel1">
- <li><a href="#introduction">Introduction</a></li>
- <li><a href="#changes">Release History</a>
- <ul class="sectlevel2">
- <li><a href="#changes_in_boost_1_69">Changes in Boost 1.69</a></li>
- <li><a href="#changes_in_boost_1_68">Changes in Boost 1.68</a></li>
- <li><a href="#changes_in_boost_1_65">Changes in Boost 1.65</a></li>
- </ul>
- </li>
- <li><a href="#rationale">Design Rationale</a></li>
- <li><a href="#reference">Reference</a>
- <ul class="sectlevel2">
- <li><a href="#ref_use_of_c11_and_c14_features">Use of C++11 and C++14 Features</a></li>
- <li><a href="#ref_macros">Macros</a></li>
- <li><a href="#ref_deprecated_names">Deprecated Names</a></li>
- <li><a href="#ref_boostsystemerror_code_hpp"><boost/system/error_code.hpp></a>
- <ul class="sectlevel3">
- <li><a href="#ref_synopsis">Synopsis</a></li>
- <li><a href="#ref_class_error_category">Class error_category</a></li>
- <li><a href="#ref_predefined_categories">Predefined Categories</a></li>
- <li><a href="#ref_class_error_code">Class error_code</a></li>
- <li><a href="#ref_class_error_condition">Class error_condition</a></li>
- <li><a href="#ref_nonmember_functions">Nonmember functions</a></li>
- </ul>
- </li>
- <li><a href="#ref_boostsystemsystem_error_hpp"><boost/system/system_error.hpp></a>
- <ul class="sectlevel3">
- <li><a href="#ref_class_system_error">Class system_error</a></li>
- </ul>
- </li>
- </ul>
- </li>
- <li><a href="#history">History</a></li>
- <li><a href="#acknowledgments">Acknowledgments</a></li>
- <li><a href="#copyright">Copyright and License</a></li>
- </ul>
- </div>
- </div>
- <div id="content">
- <div class="sect1">
- <h2 id="introduction">Introduction</h2>
- <div class="sectionbody">
- <div class="paragraph">
- <p>Error conditions originating from the operating system or other low-level
- application program interfaces (API’s) are typically reported via an integer
- representing an error code. When these low-level API calls are wrapped in
- portable code, such as in a portable library, some users want to deal with the
- error codes in portable ways. Other users need to get at the system specific
- error codes, so they can deal with system specific needs. The Boost System
- library provides simple, light-weight <code>error_code</code> objects that encapsulate
- system-specific error code values, yet also provide access to more abstract
- and portable error conditions via <code>error_condition</code> objects.</p>
- </div>
- <div class="paragraph">
- <p>Because <code>error_code</code> objects can represent errors from sources other than the
- operating system, including user-defined sources, each <code>error_code</code> and
- <code>error_condition</code> has an associated <code>error_category</code>.</p>
- </div>
- <div class="paragraph">
- <p>An exception class, <code>system_error</code>, is provided. Derived from
- <code>std::runtime_error</code>, it captures the underlying <code>error_code</code> for the problem
- causing the exception so that this important information is not lost.</p>
- </div>
- <div class="paragraph">
- <p>While exceptions are the preferred C++ default error code reporting
- mechanism, users of libraries dependent on low-level API’s often need overloads
- reporting error conditions via error code arguments and/or return values rather
- than via throwing exceptions. Otherwise, when errors are not exceptional
- occurrences and must be dealt with as they arise, programs become littered with
- try/catch blocks, unreadable, and inefficient. The Boost System library
- supports both error reporting by exception and by error code.</p>
- </div>
- <div class="paragraph">
- <p>In addition to portable errors codes and conditions supported by the
- <code>error_code.hpp</code> header, system-specific headers support the Cygwin, Linux,
- and Windows platforms. These headers are effectively no-ops if included for
- platforms other than their intended target.</p>
- </div>
- <div class="paragraph">
- <p>Boost.System is part of the C++11 Standard Library.
- A number of changes, particularly to names, were made by the C++ committee
- during standardization. The Boost implementation has been tracking those changes.
- See <a href="#ref_deprecated_names">Deprecated Names</a> for synonyms provided to prevent
- breakage of existing user code.</p>
- </div>
- </div>
- </div>
- <div class="sect1">
- <h2 id="changes">Release History</h2>
- <div class="sectionbody">
- <div class="sect2">
- <h3 id="changes_in_boost_1_69">Changes in Boost 1.69</h3>
- <div class="ulist">
- <ul>
- <li>
- <p>Boost.System is now header-only. A stub library is still built for
- compatibility, but linking to it is no longer necessary.</p>
- </li>
- <li>
- <p>Even more functions have been marked <code>constexpr</code>.</p>
- </li>
- <li>
- <p>The destructor of <code>error_category</code> is now protected and no longer
- virtual. This is a <em>potentially breaking change</em> but its impact
- is expected to be limited.</p>
- </li>
- <li>
- <p><code>error_category</code> now has a constructor that accepts a 64 bit identifier,
- enabling distinct category objects to compare equal.</p>
- </li>
- <li>
- <p>The constructors of <code>error_category</code> are now protected.</p>
- </li>
- <li>
- <p>A non-allocating, nonthrowing overload of <code>message</code> has been added.</p>
- </li>
- <li>
- <p>A virtual function <code>failed</code> has been added, allowing categories for
- which success is not synonymous with 0.</p>
- </li>
- <li>
- <p>The deprecated <code>boost::system::throws</code> object has been removed.</p>
- </li>
- <li>
- <p><code>boost::throws()</code> is now deprecated and its use is discouraged.</p>
- </li>
- <li>
- <p>The constructor of <code>system_error</code> taking a single <code>error_code</code> argument
- is now explicit.</p>
- </li>
- <li>
- <p><code>system_error::code()</code> now returns by value.</p>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect2">
- <h3 id="changes_in_boost_1_68">Changes in Boost 1.68</h3>
- <div class="paragraph">
- <p>On a C++14 compiler, many Boost.System functions and member functions
- are now <code>constexpr</code>, and <code>error_code</code> and <code>error_condition</code> are literal
- classes.</p>
- </div>
- <div class="paragraph">
- <p>In addition to enabling use in constant expressions (and <code>constexpr</code>
- functions), this significantly improves the quality of the generated code.</p>
- </div>
- <div class="paragraph">
- <p>As a result of this change, however, now using Boost.System from C++14
- or C++17 code requires that the library be also built with C++14 or
- above. This is the default on GCC 6 and newer, but not on GCC 5 or Clang.
- One can build Boost for C++14 by passing the <code>cxxstd=14</code> option to <code>b2</code>.</p>
- </div>
- <div class="paragraph">
- <p>(Previous versions allowed code built against any C++ standard to link
- with Boost.System built against any C++ standard. In 1.68, code using
- any C++ standard can link with Boost.System built with C++14 or above,
- but if Boost.System is built with C++11 or below, only code also built
- with C++11 and below can link to it successfully.)</p>
- </div>
- </div>
- <div class="sect2">
- <h3 id="changes_in_boost_1_65">Changes in Boost 1.65</h3>
- <div class="paragraph">
- <p>On a C++11 compiler, Boost.System now provides implicit conversions
- from <code>boost::system::error_category</code>, <code>error_code</code>, and <code>error_condition</code>
- to their standard equivalents from <code><system_error></code>.</p>
- </div>
- <div class="paragraph">
- <p>This allows libraries to expose a C++11 interface and report errors
- via <code>std::error_code</code> even when using Boost.System, directly or through a
- dependency such as Boost.ASIO.</p>
- </div>
- </div>
- </div>
- </div>
- <div class="sect1">
- <h2 id="rationale">Design Rationale</h2>
- <div class="sectionbody">
- <div class="paragraph">
- <p><code>error_code</code> and <code>error_condition</code> are designed as value types so
- they can be copied without slicing and do not require heap allocation, but
- still have polymorphic behavior based on the error category. This is achieved
- by abstract base class <code>error_category</code> supplying the polymorphic behavior,
- and <code>error_code</code> and <code>error_condition</code> containing a pointer to an object of a
- type derived from <code>error_category</code>.</p>
- </div>
- <div class="paragraph">
- <p>Many of the detailed design decisions were driven by the requirements that
- users to be able to add additional error categories, and that it be no more
- difficult to write portable code than system-specific code.</p>
- </div>
- <div class="paragraph">
- <p>The <code>operator<<</code> overload for <code>error_code</code> eliminates a misleading conversion to
- <code>bool</code> in code like <code>cout << ec</code>, where <code>ec</code> is of type <code>error_code</code>. It is also
- useful in its own right.</p>
- </div>
- </div>
- </div>
- <div class="sect1">
- <h2 id="reference">Reference</h2>
- <div class="sectionbody">
- <div class="sect2">
- <h3 id="ref_use_of_c11_and_c14_features">Use of C++11 and C++14 Features</h3>
- <div class="paragraph">
- <p>The library is documented to use several C++11 and C++14 features,
- including <code>noexcept</code>, explicit conversion operators and <code>constexpr</code>. The
- actual implementation uses C++11 and C++14 features only when they are
- available, and otherwise falls back on C++03 features.</p>
- </div>
- </div>
- <div class="sect2">
- <h3 id="ref_macros">Macros</h3>
- <div class="paragraph">
- <p>When <code>BOOST_SYSTEM_ENABLE_DEPRECATED</code> is defined, the library provides
- deprecated features for compatibility. These features are bound to eventually
- disappear.</p>
- </div>
- <div class="paragraph">
- <p>When <code>BOOST_SYSTEM_USE_UTF8</code> is defined, on Windows the library returns
- UTF-8 messages using code page <code>CP_UTF8</code> instead of the default <code>CP_ACP</code>.
- This macro has no effect on POSIX.</p>
- </div>
- </div>
- <div class="sect2">
- <h3 id="ref_deprecated_names">Deprecated Names</h3>
- <div class="paragraph">
- <p>In the process of adding Boost.System to the C++11 standard library, the
- C++ committee changed some names. To ease transition, Boost.System deprecates
- the old names, but will provide them when the macro <code>BOOST_SYSTEM_ENABLE_DEPRECATED</code> is defined.</p>
- </div>
- <table class="tableblock frame-all grid-all stretch">
- <colgroup>
- <col style="width: 50%;">
- <col style="width: 50%;">
- </colgroup>
- <thead>
- <tr>
- <th class="tableblock halign-left valign-top">Old usage, now deprecated</th>
- <th class="tableblock halign-left valign-top">Replacement</th>
- </tr>
- </thead>
- <tbody>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>get_generic_category()</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>generic_category()</code></p></td>
- </tr>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>get_system_category()</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>system_category()</code></p></td>
- </tr>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>namespace posix</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>namespace errc</code></p></td>
- </tr>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>namespace posix_error</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>namespace errc</code></p></td>
- </tr>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>get_posix_category()</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>generic_category()</code></p></td>
- </tr>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>posix_category</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>generic_category()</code></p></td>
- </tr>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>errno_ecat</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>generic_category()</code></p></td>
- </tr>
- <tr>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>native_ecat</code></p></td>
- <td class="tableblock halign-left valign-top"><p class="tableblock"><code>system_category()</code></p></td>
- </tr>
- </tbody>
- </table>
- </div>
- <div class="sect2">
- <h3 id="ref_boostsystemerror_code_hpp"><boost/system/error_code.hpp></h3>
- <div class="sect3">
- <h4 id="ref_synopsis">Synopsis</h4>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>namespace boost {
- namespace system {
- class error_category;
- constexpr const error_category & system_category() noexcept;
- constexpr const error_category & generic_category() noexcept;
- class error_code;
- class error_condition;
- // "Concept" helpers
- template<class T>
- struct is_error_code_enum { static const bool value = false; };
- template<class T>
- struct is_error_condition_enum { static const bool value = false; };
- // generic error conditions
- namespace errc {
- enum errc_t
- {
- success = 0,
- address_family_not_supported, //EAFNOSUPPORT
- address_in_use, //EADDRINUSE
- address_not_available, //EADDRNOTAVAIL
- already_connected, //EISCONN
- argument_list_too_long, //E2BIG
- argument_out_of_domain, //EDOM
- bad_address, //EFAULT
- bad_file_descriptor, //EBADF
- bad_message, //EBADMSG
- broken_pipe, //EPIPE
- connection_aborted, //ECONNABORTED
- connection_already_in_progress, //EALREADY
- connection_refused, //ECONNREFUSED
- connection_reset, //ECONNRESET
- cross_device_link, //EXDEV
- destination_address_required, //EDESTADDRREQ
- device_or_resource_busy, //EBUSY
- directory_not_empty, //ENOTEMPTY
- executable_format_error, //ENOEXEC
- file_exists, //EEXIST
- file_too_large, //EFBIG
- filename_too_long, //ENAMETOOLONG
- function_not_supported, //ENOSYS
- host_unreachable, //EHOSTUNREACH
- identifier_removed, //EIDRM
- illegal_byte_sequence, //EILSEQ
- inappropriate_io_control_operation, //ENOTTY
- interrupted, //EINTR
- invalid_argument, //EINVAL
- invalid_seek, //ESPIPE
- io_error, //EIO
- is_a_directory, //EISDIR
- message_size, //EMSGSIZE
- network_down, //ENETDOWN
- network_reset, //ENETRESET
- network_unreachable, //ENETUNREACH
- no_buffer_space, //ENOBUFS
- no_child_process, //ECHILD
- no_link, //ENOLINK
- no_lock_available, //ENOLCK
- no_message_available, //ENODATA
- no_message, //ENOMSG
- no_protocol_option, //ENOPROTOOPT
- no_space_on_device, //ENOSPC
- no_stream_resources, //ENOSR
- no_such_device_or_address, //ENXIO
- no_such_device, //ENODEV
- no_such_file_or_directory, //ENOENT
- no_such_process, //ESRCH
- not_a_directory, //ENOTDIR
- not_a_socket, //ENOTSOCK
- not_a_stream, //ENOSTR
- not_connected, //ENOTCONN
- not_enough_memory, //ENOMEM
- not_supported, //ENOTSUP
- operation_canceled, //ECANCELED
- operation_in_progress, //EINPROGRESS
- operation_not_permitted, //EPERM
- operation_not_supported, //EOPNOTSUPP
- operation_would_block, //EWOULDBLOCK
- owner_dead, //EOWNERDEAD
- permission_denied, //EACCES
- protocol_error, //EPROTO
- protocol_not_supported, //EPROTONOSUPPORT
- read_only_file_system, //EROFS
- resource_deadlock_would_occur, //EDEADLK
- resource_unavailable_try_again, //EAGAIN
- result_out_of_range, //ERANGE
- state_not_recoverable, //ENOTRECOVERABLE
- stream_timeout, //ETIME
- text_file_busy, //ETXTBSY
- timed_out, //ETIMEDOUT
- too_many_files_open_in_system, //ENFILE
- too_many_files_open, //EMFILE
- too_many_links, //EMLINK
- too_many_synbolic_link_levels, //ELOOP
- value_too_large, //EOVERFLOW
- wrong_protocol_type //EPROTOTYPE
- };
- } // namespace errc
- template<> struct is_error_condition_enum<errc::errc_t>
- { static const bool value = true; };
- // non-member functions
- constexpr bool operator==( const error_code & lhs,
- const error_code & rhs ) noexcept;
- bool operator==( const error_code & code,
- const error_condition & condition ) noexcept;
- bool operator==( const error_condition & condition,
- const error_code & code ) noexcept;
- constexpr bool operator==( const error_condition & lhs,
- const error_condition & rhs ) noexcept;
- constexpr bool operator!=( const error_code & lhs,
- const error_code & rhs ) noexcept;
- bool operator!=( const error_code & code,
- const error_condition & condition ) noexcept;
- bool operator!=( const error_condition & condition,
- const error_code & code ) noexcept;
- constexpr bool operator!=( const error_condition & lhs,
- const error_condition & rhs ) noexcept;
- constexpr bool operator<( const error_code & lhs,
- const error_code & rhs ) noexcept;
- constexpr bool operator<( const error_condition & lhs,
- const error_condition & rhs ) noexcept;
- constexpr error_code make_error_code( errc::errc_t e ) noexcept;
- constexpr error_condition make_error_condition( errc::errc_t e ) noexcept;
- template <class charT, class traits>
- std::basic_ostream<charT, traits>&
- operator<<( basic_ostream<charT, traits>& os, const error_code & ec );
- std::size_t hash_value( const error_code & ec );
- } // namespace system
- } // namespace boost</code></pre>
- </div>
- </div>
- <div class="paragraph">
- <p>The value of each <code>errc_t</code> constant is the same as the value of the <code><cerrno></code>
- macro shown in the above synopsis.</p>
- </div>
- <div class="paragraph">
- <p>Users may specialize <code>is_error_code_enum</code> and <code>is_error_condition_enum</code>
- templates to indicate that a type is eligible for class <code>error_code</code> and
- <code>error_condition</code> automatic conversions respectively.</p>
- </div>
- </div>
- <div class="sect3">
- <h4 id="ref_class_error_category">Class error_category</h4>
- <div class="paragraph">
- <p>The class <code>error_category</code> defines the base class for types used
- to identify the source and encoding of a particular category of error code.</p>
- </div>
- <div class="paragraph">
- <p>Classes may be derived from <code>error_category</code> to support categories of
- errors in addition to those defined in Boost.System.</p>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>namespace boost {
- namespace system {
- class error_category
- {
- public: // noncopyable
- error_category( error_category const & ) = delete;
- error_category& operator=( error_category const & ) = delete;
- protected:
- ~error_category() = default;
- constexpr error_category() noexcept;
- explicit constexpr error_category( unsigned long long id ) noexcept;
- public:
- virtual const char * name() const noexcept = 0;
- virtual error_condition default_error_condition( int ev ) const noexcept;
- virtual bool equivalent( int code, const error_condition & condition )
- const noexcept;
- virtual bool equivalent( const error_code & code, int condition )
- const noexcept;
- virtual std::string message( int ev ) const = 0;
- virtual char const * message( int ev, char * buffer, std::size_t len )
- const noexcept;
- virtual bool failed( int ev ) const noexcept;
- constexpr bool operator==( const error_category & rhs ) const noexcept;
- constexpr bool operator!=( const error_category & rhs ) const noexcept;
- constexpr bool operator< ( const error_category & rhs ) const noexcept;
- operator std::error_category const & () const;
- private:
- unsigned long long id_; // exposition only
- };
- }
- }</code></pre>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_constructors">Constructors</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr error_category() noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Effects: </dt>
- <dd>
- <p>Initializes <code>id_</code> to 0.</p>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>Since equivalence for categories that do not have an identifier is
- based on comparing object addresses, a user-defined derived category of type
- <code>C</code> that uses this constructor should ensure that only one object of type <code>C</code>
- exists in the program.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>explicit constexpr error_category( unsigned long long id ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Effects: </dt>
- <dd>
- <p>Initializes <code>id_</code> to <code>id</code>.</p>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>User-defined derived categories that use this constructor are considered
- equivalent when their identifiers match. Therefore, those categories may have more
- than one instance existing in a program, but to minimize the possibility of
- collision, their identifiers must be randomly chosen (at the time the category
- is implemented, not at runtime). One way of generating a 64 bit random identifier
- is <a href="https://www.random.org/cgi-bin/randbyte?nbytes=8&format=h" class="bare">https://www.random.org/cgi-bin/randbyte?nbytes=8&format=h</a>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_virtuals">Virtuals</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>virtual const char * name() const noexcept = 0;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p>In derived classes, a character literal naming the error category.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>virtual error_condition default_error_condition( int ev ) const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <div class="ulist">
- <ul>
- <li>
- <p>In derived classes, an error condition corresponding to <code>ev</code>.
- The returned error condition will typically come from the generic category.</p>
- </li>
- <li>
- <p>In the default implementation, <code>error_condition( ev, *this )</code>.</p>
- </li>
- </ul>
- </div>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>virtual bool equivalent( int code, const error_condition & condition )
- const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <div class="ulist">
- <ul>
- <li>
- <p>In derived classes, <code>true</code> when <code>error_code( code, *this )</code> is equivalent to <code>condition</code>.</p>
- </li>
- <li>
- <p>In the default implementation, <code>default_error_condition( code ) == condition</code>.</p>
- </li>
- </ul>
- </div>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>virtual bool equivalent( const error_code & code, int condition )
- const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <div class="ulist">
- <ul>
- <li>
- <p>In derived classes, <code>true</code> when <code>code</code> is equivalent to <code>error_condition( condition, *this )</code>.</p>
- </li>
- <li>
- <p>In the default implementation, <code>*this == code.category() && code.value() == condition</code>.</p>
- </li>
- </ul>
- </div>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>virtual std::string message( int ev ) const = 0;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p>In derived classes, a string that describes the error denoted by <code>ev</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>virtual char const * message( int ev, char * buffer, std::size_t len )
- const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Effects: </dt>
- <dd>
- <div class="ulist">
- <ul>
- <li>
- <p>Derived classes should either</p>
- <div class="ulist">
- <ul>
- <li>
- <p>return a pointer to a character literal describing the error denoted by <code>ev</code>, or</p>
- </li>
- <li>
- <p>copy a string describing the error into <code>buffer</code>, truncating it to <code>len-1</code>
- characters and storing a null terminator, and return <code>buffer</code>. If <code>len</code> is 0,
- nothing is copied, but the function still returns <code>buffer</code>. Note that
- when <code>len</code> is 0, <code>buffer</code> may be <code>nullptr</code>.</p>
- </li>
- </ul>
- </div>
- </li>
- <li>
- <p>The default implementation calls <code>message(ev)</code> and copies the result into
- <code>buffer</code>, truncating it to <code>len-1</code> characters and storing a null terminator.
- If <code>len</code> is 0, copies nothing. Returns <code>buffer</code>. If <code>message(ev)</code> throws an
- exception, the string <code>"Message text unavailable"</code> is used.</p>
- </li>
- </ul>
- </div>
- </dd>
- <dt class="hdlist1">Example: </dt>
- <dd>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>const char* my_category::message(int ev, char* buffer, size_t len) const noexcept
- {
- switch(ev)
- {
- case 0: return "no error";
- case 1: return "voltage out of range";
- case 2: return "impedance mismatch";
- case 31:
- case 32:
- case 33:
- std::snprintf(buffer, len, "component %d failure", ev-30);
- return buffer;
- default:
- std::snprintf(buffer, len, "unknown error %d", ev);
- return buffer;
- }
- }</code></pre>
- </div>
- </div>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>virtual bool failed( int ev ) const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <div class="ulist">
- <ul>
- <li>
- <p>In derived classes, <code>true</code> when <code>ev</code> represents a failure.</p>
- </li>
- <li>
- <p>In the default implementation, <code>ev != 0</code>.</p>
- </li>
- </ul>
- </div>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>All calls to this function with the same <code>ev</code> must return the same value.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_nonvirtuals">Nonvirtuals</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool operator==( const error_category & rhs ) const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>rhs.id_ == 0? this == &rhs: id_ == rhs.id_</code>.</p>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>Two category objects are considered equivalent when they have matching
- nonzero identifiers, or are the same object.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool operator!=( const error_category & rhs ) const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>!( *this == rhs )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool operator< ( const error_category & rhs ) const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <div class="ulist">
- <ul>
- <li>
- <p>If <code>id_ < rhs.id_</code>, <code>true</code>;</p>
- </li>
- <li>
- <p>Otherwise, if <code>id_ > rhs.id_</code>, <code>false</code>;</p>
- </li>
- <li>
- <p>Otherwise, if <code>rhs.id_ != 0</code>, <code>false</code>;</p>
- </li>
- <li>
- <p>Otherwise, <code>std::less<error_category const *>()( this, &rhs )</code>.</p>
- </li>
- </ul>
- </div>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>operator std::error_category const & () const;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p>A reference to an <code>std::error_category</code> object corresponding
- to <code>*this</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- </div>
- <div class="sect3">
- <h4 id="ref_predefined_categories">Predefined Categories</h4>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr const error_category & system_category() noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p>A reference to an <code>error_category</code> object identifying errors
- originating from the operating system.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr const error_category & generic_category() noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p>A reference to an <code>error_category</code> object identifying portable
- error conditions.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect3">
- <h4 id="ref_class_error_code">Class error_code</h4>
- <div class="paragraph">
- <p>The class <code>error_code</code> describes an object used to hold error code
- values, such as those originating from the operating system or other
- low-level application program interfaces. It’s an adjunct to error reporting
- by exception.</p>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>namespace boost {
- namespace system {
- class error_code {
- public:
- // constructors:
- constexpr error_code() noexcept;
- constexpr error_code( int val, const error_category & cat ) noexcept;
- template <class ErrorCodeEnum>
- constexpr error_code( ErrorCodeEnum e ) noexcept;
- // modifiers:
- constexpr void assign( int val, const error_category & cat ) noexcept;
- template<typename ErrorCodeEnum>
- constexpr error_code & operator=( ErrorCodeEnum e ) noexcept;
- constexpr void clear() noexcept;
- // observers:
- constexpr int value() const noexcept;
- constexpr const error_category & category() const noexcept;
- error_condition default_error_condition() const noexcept;
- std::string message() const;
- char const * message( char * buffer, std::size_t len ) const noexcept;
- constexpr bool failed() const noexcept;
- constexpr explicit operator bool() const noexcept;
- operator std::error_code() const;
- private: // exposition only
- int val_;
- const error_category * cat_;
- };
- }
- }</code></pre>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_constructors_2">Constructors</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr error_code() noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == 0</code>; <code>*cat_ == system_category()</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr error_code( int val, const error_category & cat ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == val</code>; <code>cat_ == &cat</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>template <class ErrorCodeEnum>
- constexpr error_code( ErrorCodeEnum e ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>*this == make_error_code( e )</code>.</p>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>This constructor is only enabled when <code>is_error_code_enum<ErrorCodeEnum>::value</code> is <code>true</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_modifiers">Modifiers</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr void assign( int val, const error_category & cat ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == val</code>; <code>cat_ == &cat</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>template<typename ErrorCodeEnum>
- constexpr error_code & operator=( ErrorCodeEnum e ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>*this == make_error_code( e )</code>.</p>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>This operator is only enabled when <code>is_error_code_enum<ErrorCodeEnum>::value</code> is <code>true</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr void clear() noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == 0</code>; <code>*cat_ == system_category()</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_observers">Observers</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr int value() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>val_</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr const error_category & category() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>*cat_</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>error_condition default_error_condition() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>cat_->default_error_condition( val_ )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>std::string message() const;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>cat_->message( val_ )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>char const * message( char * buffer, std::size_t len ) const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>cat_->message( val_, buffer, len )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool failed() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>cat_->failed( val_ )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr explicit operator bool() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>val_ != 0</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>operator std::error_code() const;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>std::error_code( val_, *cat_ )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- </div>
- <div class="sect3">
- <h4 id="ref_class_error_condition">Class error_condition</h4>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>namespace boost {
- namespace system {
- class error_condition {
- public:
- // constructors:
- constexpr error_condition() noexcept;
- constexpr error_condition( int val, const error_category & cat ) noexcept;
- template <class ErrorConditionEnum>
- constexpr error_condition( ErrorConditionEnum e ) noexcept;
- // modifiers:
- constexpr void assign( int val, const error_category & cat ) noexcept;
- template<typename ErrorConditionEnum>
- constexpr error_condition & operator=( ErrorConditionEnum e ) noexcept;
- constexpr void clear() noexcept;
- // observers:
- constexpr int value() const noexcept;
- constexpr const error_category & category() const noexcept;
- std::string message() const;
- char const * message( char * buffer, std::size_t len ) const noexcept;
- constexpr bool failed() const noexcept;
- constexpr explicit operator bool() const noexcept;
- operator std::error_condition() const;
- private: // exposition only
- int val_;
- const error_category * cat_;
- };
- }
- }</code></pre>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_constructors_3">Constructors</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr error_condition() noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == 0</code>; <code>*cat_ == generic_category()</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr error_condition( int val, const error_category & cat ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == val</code>; <code>cat_ == &cat</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>template <class ErrorConditionEnum>
- constexpr error_condition( ErrorConditionEnum e ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>*this == make_error_condition( e )</code>.</p>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>This constructor is only enabled when <code>is_error_condition_enum<ErrorConditionEnum>::value</code> is <code>true</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_modifiers_2">Modifiers</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr void assign( int val, const error_category & cat ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == val</code>; <code>cat_ == &cat</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>template <class ErrorConditionEnum>
- constexpr error_condition & operator=( ErrorConditionEnum e ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>*this == make_error_condition( e )</code>.</p>
- </dd>
- <dt class="hdlist1">Remarks: </dt>
- <dd>
- <p>This operator is only enabled when <code>is_error_condition_enum<ErrorConditionEnum>::value</code> is <code>true</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr void clear() noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>val_ == 0</code>; <code>*cat_ == generic_category()</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_observers_2">Observers</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr int value() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>val_</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr const error_category & category() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>*cat_</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>std::string message() const;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>cat_->message( val_ )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>char const * message( char * buffer, std::size_t len ) const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>cat_->message( val_, buffer, len )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool failed() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>cat_->failed( val_ )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr explicit operator bool() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>val_ != 0</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>operator std::error_condition() const;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>std::error_condition( val_, *cat_ )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- </div>
- <div class="sect3">
- <h4 id="ref_nonmember_functions">Nonmember functions</h4>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool operator==( const error_code & lhs,
- const error_code & rhs ) noexcept;
- constexpr bool operator==( const error_condition & lhs,
- const error_condition & rhs ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>lhs.value() == rhs.value() && lhs.category() == rhs.category()</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>bool operator==( const error_code & code,
- const error_condition & condition ) noexcept;
- bool operator==( const error_condition & condition,
- const error_code & code ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>code.category().equivalent( code.value(), condition ) || condition.category().equivalent( code, condition.value() )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool operator!=( const error_code & lhs,
- const error_code & rhs ) noexcept;
- constexpr bool operator!=( const error_condition & lhs,
- const error_condition & rhs ) noexcept;
- bool operator!=( const error_code & code,
- const error_condition & condition ) noexcept;
- bool operator!=( const error_condition & condition,
- const error_code & code ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>!( lhs == rhs )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr bool operator<( const error_code & lhs,
- const error_code & rhs ) noexcept;
- constexpr bool operator<( const error_condition & lhs,
- const error_condition & rhs ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>lhs.category() < rhs.category() || ( lhs.category() == rhs.category() && lhs.value() < rhs.value() )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr error_code make_error_code( errc::errc_t e ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>error_code( e, generic_category() )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>constexpr error_condition make_error_condition( errc::errc_t e ) noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>error_condition( e, generic_category() )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>template <class charT, class traits>
- std::basic_ostream<charT, traits>&
- operator<<( basic_ostream<charT, traits>& os, const error_code & ec );</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Effects: </dt>
- <dd>
- <p><code>os << ec.category().name() << ':' << ec.value()</code>.</p>
- </dd>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>os</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>std::size_t hash_value( const error_code & ec );</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p>A hash value representing <code>ec</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- </div>
- <div class="sect2">
- <h3 id="ref_boostsystemsystem_error_hpp"><boost/system/system_error.hpp></h3>
- <div class="sect3">
- <h4 id="ref_class_system_error">Class system_error</h4>
- <div class="paragraph">
- <p>The class <code>system_error</code> describes an exception object used to
- report errors that have an associated <code>error_code</code>. Such errors
- typically originate from operating system or other low-level
- application program interfaces.</p>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>namespace boost
- {
- namespace system
- {
- class system_error: public std::runtime_error
- {
- public:
- explicit system_error( error_code ec );
- system_error( error_code ec, const char * what_arg );
- system_error( error_code ec, const std::string & what_arg );
- system_error( int ev, const error_category & ecat );
- system_error( int ev, const error_category & ecat,
- const char * what_arg );
- system_error( int ev, const error_category & ecat,
- const std::string & what_arg );
- error_code code() const noexcept;
- const char * what() const noexcept;
- };
- }
- }</code></pre>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_constructors_4">Constructors</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>explicit system_error( error_code ec );
- system_error( error_code ec, const char * what_arg );
- system_error( error_code ec, const std::string & what_arg );</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>code() == ec</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>system_error( int ev, const error_category & ecat,
- const char * what_arg );
- system_error( int ev, const error_category & ecat,
- const std::string & what_arg );
- system_error( int ev, const error_category & ecat );</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Ensures: </dt>
- <dd>
- <p><code>code() == error_code( ev, ecat )</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- <div class="sect4">
- <h5 id="ref_observers_3">Observers</h5>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>error_code code() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p><code>ec</code> or <code>error_code( ev, ecat )</code>, from the constructor, as appropriate.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- <div class="listingblock">
- <div class="content">
- <pre class="highlight"><code>const char * what() const noexcept;</code></pre>
- </div>
- </div>
- <div class="ulist none">
- <ul class="none">
- <li>
- <p></p>
- <div class="dlist">
- <dl>
- <dt class="hdlist1">Returns: </dt>
- <dd>
- <p>A null-terminated character string incorporating the arguments supplied
- in the constructor, typically of the form <code>what_arg + ": " + code.message()</code>.</p>
- </dd>
- </dl>
- </div>
- </li>
- </ul>
- </div>
- </div>
- </div>
- </div>
- </div>
- </div>
- <div class="sect1">
- <h2 id="history">History</h2>
- <div class="sectionbody">
- <div class="paragraph">
- <p><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1975.html">N1975</a>,
- Filesystem Library Proposal for TR2, accepted for Library Technical
- Report 2 (TR2) at the Berlin meeting, included additional components to
- supplement the Standard Library’s Diagnostics clause. Since then, these error
- reporting components have received wider public scrutiny and enhancements have
- been made to the design. The enhanced version has been used by
- <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2054.pdf">N2054</a>,
- Networking Library Proposal for TR2, demonstrating that these error reporting
- components are useful beyond the original Filesystem Library.</p>
- </div>
- <div class="paragraph">
- <p>The original proposal viewed error categories as a binary choice between
- <code>errno</code> (i.e. POSIX-style) and the native operating system’s error
- codes. The proposed components now allow as many additional error categories as
- are needed by either implementations or by users. The need to support additional
- error categories, for example, occurs in some networking library implementations
- because they are built on top of the POSIX <code>getaddrinfo</code> API that
- uses error codes not based on <code>errno</code>.</p>
- </div>
- </div>
- </div>
- <div class="sect1">
- <h2 id="acknowledgments">Acknowledgments</h2>
- <div class="sectionbody">
- <div class="paragraph">
- <p>Christopher Kohlhoff and Peter Dimov made important contributions to the
- design. Comments and suggestions were also received from Pavel Vozenilek,
- Gennaro Prota, Dave Abrahams, Jeff Garland, Iain Hanson, Oliver Kowalke, and
- Oleg Abrosimov. Christopher Kohlhoff suggested several improvements to the
- <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2066.html">N2066</a>
- paper. Johan Nilsson’s comments led to several of the refinements in N2066.</p>
- </div>
- </div>
- </div>
- <div class="sect1">
- <h2 id="copyright">Copyright and License</h2>
- <div class="sectionbody">
- <div class="paragraph">
- <p>This documentation is</p>
- </div>
- <div class="ulist">
- <ul>
- <li>
- <p>Copyright 2003-2017 Beman Dawes</p>
- </li>
- <li>
- <p>Copyright 2018 Peter Dimov</p>
- </li>
- </ul>
- </div>
- <div class="paragraph">
- <p>and is distributed under the <a href="http://www.boost.org/LICENSE_1_0.txt">Boost Software License, Version 1.0</a>.</p>
- </div>
- </div>
- </div>
- </div>
- <div id="footer">
- <div id="footer-text">
- Last updated 2019-12-10 00:19:59 UTC
- </div>
- </div>
- <style>
- *:not(pre)>code { background: none; color: #600000; }
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- </body>
- </html>
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