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<font size="7">System Library</font>
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Reference</a></td>
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<i><b>Contents</b></i></td>
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<tr>
<td width="100%" bgcolor="#E8F5FF">
<a href="#Introduction">Introduction</a><br>
<a href="#Macros">Macros</a><br>
<a href="#Deprecated-names">Deprecated names</a><br>
<a href="#Header-error_code">Header <boost/system/error_code.hpp></a><br>
<a href="#Class-error_category">Class <code>error_category</code></a><br>
<a href="#Class-error_category-synopsis">Class <code>error_category</code> synopsis</a><br>
<a href="#Class-error_category-virtual-members">Class <code>error_category</code> virtual members</a><br>
<a href="#Class-error_category-non-virtual-members">Class <code>error_category</code> non-virtual members</a><br>
<a href="#Class-error_category-non-member-functions">Class <code>error_category</code>
non-member functions</a><br>
<a href="#Class-error_category-predefined-objects">Class <code>error_category</code> predefined objects</a><br>
<a href="#Class-error_code">Class <code>error_code</code></a><br>
<a href="#Class-error_code-synopsis">Class <code>error_code</code> synopsis</a><br>
<a href="#Class-error_code-constructors">Class <code>error_code</code> constructors</a><br>
<a href="#Class-error_code-modifiers">Class <code>error_code</code> modifiers</a><br>
<a href="#Class-error_code-observers">Class <code>error_code</code> observers</a><br>
<a href="#Class-error_condition</code>">Class <code>error_condition</code></a><br>
<a href="#Class-error_condition-synopsis">Class <code>error_condition</code> synopsis</a><br>
<a href="#Class-error_condition-constructors">Class <code>error_condition</code> constructors</a><br>
<a href="#Class-error_condition-modifiers">Class <code>error_condition</code> modifiers</a><br>
<a href="#Class-error_condition-observers">Class <code>error_condition</code> observers</a><br>
<a href="#throws-object"><code>throws</code> object</a><br>
<a href="#Semantics-of-throws">Semantics of <code>throws</code> object</a><br>
<a href="#Non-member-functions">Non-member functions</a><br>
<a href="#Header-system_error">Header <boost/system/system_error.hpp></a><br>
<a href="#Class-system_error">Class <code>system_error</code></a><br>
</td>
</tr>
</table>
<h2><a name="Introduction">Introduction</a></h2>
<p>This reference documentation describes components that
programs may use to report error conditions originating from the operating
system or other low-level application program interfaces.</p>
<p>Boost.System library components never change the value of <code>
errno</code>.</p>
<h2><a name="Macros">Macros</a></h2>
<p>Users may defined the following macros if desired. Sensible defaults are
provided, so users may ignore these macros if they prefer.</p>
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111">
<tr>
<td><b><i>Macro Name</i></b></td>
<td><b><i>Default</i></b></td>
<td><b><i>Effect if defined</i></b></td>
</tr>
<tr>
<td valign="top"><code>BOOST_WINDOWS_API</code></td>
<td valign="top">Defined if Windows is detected by Boost.System's automatic configuration
code, otherwise not defined.</td>
<td valign="top">Implementation uses the Microsoft Windows native
application program interface (API).</td>
</tr>
<tr>
<td valign="top"><code>BOOST_POSIX_API</code></td>
<td valign="top">Defined if Windows is not detected by Boost.System's automatic configuration
code.</td>
<td valign="top">Implementation uses the POSIX native
application program interface (API).</td>
</tr>
<tr>
<td valign="top"><code>BOOST_SYSTEM_DYN_LINK</code></td>
<td valign="top">Defined if <code>BOOST_ALL_DYN_LINK</code> is defined,
otherwise not defined.</td>
<td valign="top">Boost.System library is dynamically linked. If not defined,
static linking is assumed.</td>
</tr>
<tr>
<td valign="top"><code>BOOST_SYSTEM_NO_LIB</code></td>
<td valign="top">Defined if <code>BOOST_ALL_NO_LIB</code> is defined,
otherwise not defined.</td>
<td valign="top">Boost.System library does not use the Boost auto-link
facility.</td>
</tr>
<tr>
<td valign="top"><code>BOOST_SYSTEM_NO_DEPRECATED</code></td>
<td valign="top">Not defined.</td>
<td valign="top">Deprecated features are excluded.</td>
</tr>
</table>
<h2><a name="Deprecated-names">Deprecated names</a></h2>
<p>In the process of adding Boost.System to C++0x standard library, some of the
names are being changed. To ease transition, Boost.System deprecates the old
names, but continues to provide them unless macro <code>BOOST_SYSTEM_NO_DEPRECATED</code>
is defined.</p>
<table border="1" cellpadding="5" cellspacing="1" style="border-collapse: collapse" bordercolor="#111111">
<tr>
<td><b><i>Old name, now deprecated</i></b></td>
<td><b><i>New name</i></b></td>
</tr>
<tr>
<td><code>namespace posix</code></td>
<td><code>namespace errc</code></td>
</tr>
<tr>
<td><code>namespace posix_error</code></td>
<td><code>namespace errc</code></td>
</tr>
<tr>
<td><code>enum posix_errno</code></td>
<td><code>enum errc_t</code></td>
</tr>
<tr>
<td><code>get_posix_category()</code></td>
<td><code>get_generic_category()</code></td>
</tr>
<tr>
<td><code>posix_category</code></td>
<td><code>generic_category</code></td>
</tr>
<tr>
<td><code>errno_ecat</code></td>
<td><code>generic_category</code></td>
</tr>
<tr>
<td><code>native_ecat</code></td>
<td><code>system_category</code></td>
</tr>
</table>
<h2><a name="Header-error_code">Header <boost/system/error_code.hpp></a></h2>
<h3><boost/system/error_code.hpp> synopsis</h3>
<blockquote>
<pre>namespace boost
{
namespace system
{
class <a href="#Class-error_category">error_category</a>;
class <a href="#Class-error_code">error_code</a>;
class <a href="#Class-error_condition">error_condition</a>;
// "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<posix::posix_errno><errc::errc_t>
{ static const bool value = true; };
// predefined error_code object used as "throw on error" tag
extern error_code <a href="#throws-object">throws</a>;
// <a href="#Non-member-functions">non-member functions</a>
bool operator==( const error_code & lhs, const error_code & rhs );
bool operator==( const error_code & code, const error_condition & condition );
bool operator==( const error_condition & condition, const error_code & code );
bool operator==( const error_condition & lhs, const error_condition & rhs );
bool operator!=( const error_code & lhs, const error_code & rhs );
bool operator!=( const error_code & code, const error_condition & condition );
bool operator!=( const error_condition & condition, const error_code & code );
bool operator!=( const error_condition & lhs, const error_condition & rhs );
bool operator<( const error_code & lhs, const error_code & rhs );
bool operator<( const error_condition & lhs, const error_condition & rhs );
error_code make_error_code( errc::errc_t e );
error_condition make_error_condition( errc::errc_t e );
template <class charT, class traits>
std::basic_ostream<charT,traits>&
operator<<( basic_ostream<charT,traits>& os, const error_code & ec );
size_t hash_value( const error_code & ec );
}
}</pre>
</blockquote>
<p>The value of each<code> errc_t</code> constant shall be the same as the
value of the <code><cerrno></code> macro shown in the above synopsis.</p>
<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>
<h2><a name="Class-error_category">Class <code>error_category</code></a></h2>
<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>
<p><i>[Note:</i> Classes may be derived from <code>error_category</code>
to support additional categories of errors. <i>--end note]</i></p>
<p>The class <code>error_category</code> serves as a base class for types used
to identify the source and encoding of a particular category of error code.
Classes may be derived from <code>error_category</code> to support categories of
errors in addition to those defined in the Boost System library. Such classes
shall behave as specified in this subclause. [<i> Note:</i> <code>error_category</code>
objects are passed by reference, and two such objects are equal if they have the
same address. This means that applications using custom <code>error_category</code>
types should create a single object of each such type. <i>end note</i> ]</p>
<h3><a name="Class-error_category-synopsis">Class <code>error_category</code> synopsis</a></h3>
<blockquote>
<pre>namespace boost
{
namespace system
{
class error_category : public noncopyable
{
public:
virtual ~error_category();
virtual const char * name() const = 0;
virtual string message( int ev ) const = 0;
virtual error_condition default_error_condition( int ev ) const;
virtual bool equivalent( int code, const error_condition & condition ) const;
virtual bool equivalent( const error_code & code, int condition ) const;
bool operator==( const error_category & rhs ) const;
bool operator!=( const error_category & rhs ) const;
bool operator< ( const error_category & rhs ) const;
};
const error_category & get_system_category();
const error_category & get_generic_category();
static const error_category & system_category = get_system_category();
static const error_category & generic_category = get_generic_category();
}
}</pre>
</blockquote>
<h3><a name="Class-error_category-virtual-members">Class <code>error_category</code> virtual members</a></h3>
<p>Classes derived from <code>error_category</code> shall behave as specified in
this subclause.</p>
<pre>virtual const char * name() const=0;</pre>
<blockquote>
<p><i>Returns: </i>a string naming the error category.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>virtual string message( int ev ) const=0;</pre>
<blockquote>
<p><i>Returns:</i> A string that describes the error denoted by
<code>ev</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>virtual error_condition default_error_condition( int ev ) const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>error_condition( ev, *this )</code>.</p>
<blockquote>
<p> [<i>--Note:</i> Derived classes will typically convert <code>ev</code>
to some portable <code>error_category</code>, such as <code>generic_category</code>,
and return it as an <code>error_condition</code> for that category. <i>--end
note</i>]</p>
</blockquote>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>virtual bool equivalent( int code, const error_condition &
condition )
const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>default_error_condition( code ) == condition</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>virtual bool equivalent( const error_code & code, int condition ) const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>*this == code.category() && code.value() == condition</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<h3><a name="Class-error_category-non-virtual-members">Class <code>error_category</code> non-virtual members</a></h3>
<p><code>bool operator==( const error_category & rhs ) const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>this == &rhs</code>.</p>
</blockquote>
<p><code>bool operator!=( const error_category & rhs ) const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>this != &rhs</code>.</p>
</blockquote>
<pre>bool operator<( const error_category & rhs ) const;</pre>
<blockquote>
<p><i>Returns:</i> <code>std::less<const error_category*>()( this, &rhs )</code>.</p>
<blockquote>
<p><i>[Note:</i> <code>std::less</code> provides a total ordering for
pointers. <i>--end note]</i></p>
</blockquote>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<h3><a name="Class-error_category-non-member-functions">Class <code>error_category</code>
non-member functions</a></h3>
<pre>const error_category & get_system_category();</pre>
<blockquote>
<p><i>Returns:</i> A reference to a <code>error_category</code> object
identifying errors originating from the operating system.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>const error_category & get_generic_category();</pre>
<blockquote>
<p><i>Returns:</i> A reference to a <code>error_category</code> object
identifying portable error conditions.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<h3><a name="Class-error_category-predefined-objects">Class <code>error_category</code>
predefined objects</a></h3>
<p>Predefined objects <code>system_category</code>
and <code>generic_category</code> identify system specific error codes and portable error conditions, respectively.</p>
<h2><a name="Class-error_code">Class <code>
error_code</code></a></h2>
<p>The class <code>error_code</code> describes an object used to hold error code
values, such as those originating from the operating<br>
system or other low-level application program interfaces. <i>[ Note: </i>Class
<code>error_code</code> is an adjunct to error reporting by<br>
exception. <i>end note ]</i></p>
<h3><a name="Class-error_code-synopsis">Class <code>
error_code</code> synopsis</a></h3>
<blockquote>
<pre>namespace boost
{
namespace system
{
class error_code {
public:
// constructors:
error_code();
error_code( val, const error_category & cat );
template <class <code>ErrorCodeEnum</code>>
error_code(<code> ErrorCodeEnum</code> e,
typename enable_if<is_error_code_enum<<code>ErrorCodeEnum</code>> >::type* = 0);
// modifiers:
void assign( int val, const error_category & cat );
template<typename <code>ErrorCodeEnum</code>>
typename enable_if<is_error_code_enum<<code>ErrorCodeEnum</code>>, error_code>::type &
operator=( <code>ErrorCodeEnum</code> val );;
void clear();
// observers:
int value() const;
cont error_category & category() const;
error_condition default_error_condition() const;
string message() const;
operator unspecified-bool-type() const;
private:
int val_; // <i>exposition only</i>
const error_category * cat_; // <i>exposition only</i>
};
}
}</pre>
</blockquote>
<h3><a name="Class-error_code-constructors">Class <code>
error_code</code> constructors</a></h3>
<pre>error_code();</pre>
<blockquote>
<p><i>Effects: </i>Constructs an object of type <code>error_code</code>.</p>
<p><i>Postconditions:</i> <code>val_ == 0 && cat_ == &system_category</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>error_code( int val, const error_category & cat );</pre>
<blockquote>
<p><i>Effects: </i>Constructs an object of type <code>error_code</code>.</p>
<p><i>Postconditions:</i> <code>val_ == val && cat_ == &cat</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>template <class <code>ErrorCodeEnum</code>>
error_code(<code> errorCodeEnum</code> val,
typename enable_if<is_error_code_enum<<code>ErrorCodeEnum</code>> >::type* = 0);</pre>
<blockquote>
<p><i>Effects: </i>Constructs an object of type <code>error_code</code>.</p>
<p><i>Postconditions:</i> <code>*this == make_error_code( val )</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<h3><a name="Class-error_code-modifiers">Class <code>
error_code</code> modifiers</a></h3>
<pre>void assign( int val, const error_category & cat );</pre>
<blockquote>
<p><i>Postconditions:</i> <code>val_ == val && cat_ == &cat</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>template<typename <code>ErrorCodeEnum</code>>
typename enable_if<is_error_code_enum<<code>ErrorCodeEnum</code>>, error_code>::type &
operator=( <code>ErrorCodeEnum</code> val );</pre>
<blockquote>
<p><i>Postconditions:</i> <code>*this == make_error_code( val )</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>void clear();</code></p>
<blockquote>
<p><i>postcondition:</i> <code>value() == 0 && category() == generic_category</code></p>
</blockquote>
<h3><a name="Class-error_code-observers">Class <code>
error_code</code> observers</a></h3>
<p><code>int value() const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>val_</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>const error_category & category() const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>*cat_</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>error_condition default_error_condition() const;</pre>
<blockquote>
<p><i>Returns:</i> <code>category().default_error_condition( value())</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>string message() const;</code></p>
<blockquote>
<p><i>Returns:</i> <code>category().message( value())</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>operator <i>unspecified-bool-type</i>() const;</code></p>
<blockquote>
<p><i>Returns:</i> if <code>value() != 0</code>, returns a value that will evaluate
<code>true</code> in a boolean context; otherwise, returns a value that will
evaluate <code>false</code> in a boolean context. The value type returned shall
not be convertible to <code>int</code>.</p>
<p><i>Throws:</i> nothing.</p>
<p><i>[Note: </i>This conversion can be used in contexts where a <code>bool</code>
is expected ( e.g., an <code>if</code> condition ); however, implicit conversions
( e.g., to <code>int</code>) that can occur with <code>bool</code> are not
allowed, eliminating some sources of user error. One possible implementation
choice for this type is pointer-to-member. <i>--end note ]</i></p>
</blockquote>
<h2><a name="Class-error_condition">Class <code>error_condition</code></a></h2>
<p>The class <code>error_condition</code> describes an object used to hold
values identifying error conditions. <i>[ Note: </i><code>error_condition</code>
values are portable abstractions, while <code>error_code</code> values are
implementation specific. <i>--end note ]</i></p>
<h3><a name="Class-error_condition-synopsis">Class <code>error_condition</code> synopsis</a></h3>
<blockquote>
<pre>namespace boost
{
namespace system
{
class error_condition
{
public:
// constructors:
error_condition();
error_condition( int val, const error_category & cat );
template <class ErrorConditionEnum>
error_condition( errorConditionEnum val,
typename enable_if<is_error_condition_enum<ErrorConditionEnum> >::type* = 0 );
// modifiers:
void assign( int val, const error_category & cat );
template<typename ErrorConditionEnum>
typename enable_if<is_error_condition_enum<ErrorConditionEnum>, error_code>::type &
operator=( ErrorConditionEnum val );
void clear();
// observers:
int value() const;
const error_category & category() const;
string message() const;
operator unspecified-bool-type () const;
private:
int val_; // <i>exposition only</i>
const error_category * cat_; // <i>exposition only</i>
};
}
}</pre>
</blockquote>
<h3><a name="Class-error_condition-constructors">Class <code>error_condition</code>
constructors</a></h3>
<pre>error_condition(); </pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of type <code>error_condition</code>.</p>
<p><i>Postconditions:</i> <code>val_ == 0 and cat_ == &generic_category</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>error_condition( int val, const error_category & cat );</pre>
<blockquote>
<p><i>Effects: </i>Constructs an object of type error_condition.</p>
<p><i>Postconditions:</i> <code>val_ == val and cat_ == &cat</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>template <class ErrorConditionEnum>
error_condition( errorConditionEnum val,
typename enable_if<is_error_condition_enum<ErrorConditionEnum> >::type* = 0 );</pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of type <code>error_condition</code>.</p>
<p><i>Postconditions:</i> <code>*this == make_error_condition( val )</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<h3><a name="Class-error_condition-modifiers">Class <code>error_condition</code>
modifiers</a></h3>
<pre>void assign( int val, const error_category & cat ); </pre>
<blockquote>
<p><i>Postconditions:</i> <code>val_ == val and cat_ == &cat</code>. </p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>template<typename ErrorConditionEnum>
typename enable_if<is_error_condition_enum<ErrorConditionEnum>, error_code>::type &
operator=( ErrorConditionEnum val );</pre>
<blockquote>
<p><i>Postconditions:</i> <code>*this == make_error_condition( val )</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<p><code>void clear();</code></p>
<blockquote>
<p><i>postcondition:</i> <code>value() == 0 && category() == generic_category</code></p>
</blockquote>
<h3><a name="Class-error_condition-observers">Class <code>error_condition</code>
observers</a></h3>
<pre>int value() const;</pre>
<blockquote>
<p><i>Returns:</i> <code>val_</code>.</p>
<p><i>Throws:</i> Nothing</p>
</blockquote>
<pre>const error_category & category() const;</pre>
<blockquote>
<p><i>Returns:</i> <code>*cat_</code>.</p>
<p>Throws: Nothing.</p>
</blockquote>
<pre>string message() const;</pre>
<blockquote>
<p><i>Returns:</i> <code>category().message( value() )</code>.</p>
<p><i>Throws:</i> Nothing.</p>
</blockquote>
<pre>operator unspecified-bool-type () const;</pre>
<blockquote>
<p><i>Returns: </i>If <code>value() != 0</code>, returns a value that will
evaluate <code>true</code> in a boolean context; otherwise, returns a value
that will evaluate <code>false</code>. The return type shall not be
convertible to <code>int</code>. </p>
<p><i>Throws:</i> Nothing.</p>
<p><i> [ Note:</i> This conversion can be used in contexts where a <code>bool</code>
is expected ( e.g., an if condition ); however, implicit conversions ( e.g., to
<code>int</code>) that can occur with <code>bool</code> are not allowed,
eliminating some sources of user error. One possible implementation choice for
this type is pointer to member. <i>--end note</i> <i>]</i></p>
</blockquote>
<h2><a name="throws-object"><code>throws</code> object</a></h2>
<pre>extern error_code throws;</pre>
<p>The predefined <code>error_code</code> object <code>throws</code> is supplied
for use as a "throw on error" tag.</p>
<h2><a name="Semantics-of-throws">Semantics of <code>throws</code></a> object</h2>
<p>Functions that specify an argument in the form <code>error_code& ec=throws</code>,
with appropriate namespace qualifiers, have the following error handling
semantics:</p>
<blockquote>
<p><i>Postconditions:</i></p>
<blockquote>
<p>If <code>&ec != &throws</code> and an error occurred:</p>
<ul>
<li> <code>ec.value()</code> returns the implementation specific error
number for the particular error that occurred.</li>
<li><code>ec.category()</code> returns the <code>
<a href="#Class-error_category">error_category</a></code> for <code>ec.value()</code>.</li>
</ul>
<p>if <code>&ec != &throws</code> and an error did not occur, <code>ec.clear()</code>.</p>
</blockquote>
<p><i>Throws:</i></p>
<blockquote>
<p>If an error occurs and <code>&ec == &throws</code>, throws an exception of type
<code><a href="#Class-system_error">system_error</a></code> or of a type
derived from <code><a href="#Class-system_error">system_error</a></code>. The
exception's <code>code()</code> member function returns a reference to an
<code>error_code</code> object with the behavior specified in <i>
Postconditions</i>.</p>
</blockquote>
</blockquote>
<h2><a name="Non-member-functions">Non-member functions</a></h2>
<pre>bool operator==( const error_code & lhs, const error_code & rhs );</pre>
<blockquote>
<p><i>Returns:</i> <code>lhs.category() == rhs.category() && lhs.value() ==
rhs.value()</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>bool operator==( const error_code & code, const error_condition & condition );
bool operator==( const error_condition & condition, const error_code & code );</pre>
<blockquote>
<p><i>Returns:</i> <code>code.category().equivalent( code.value(), condition )<br>
|| condition.category().equivalent( code, condition.value() )</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>bool operator==( const error_condition & lhs, const error_condition & rhs );</pre>
<blockquote>
<p><i>Returns:</i> <code>lhs.category() == rhs.category() && lhs.value() ==
rhs.value()</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>bool operator!=( const error_code & lhs, const error_code & rhs );</pre>
<blockquote>
<p><i>Returns:</i> <code>!(lhs == rhs )</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>bool operator!=( const error_code & code, const error_condition & condition );
bool operator!=( const error_condition & condition, const error_code & code );</pre>
<blockquote>
<p><i>Returns:</i><code> !( code == condition )</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>bool operator!=( const error_condition & lhs, const error_condition & rhs );</pre>
<blockquote>
<p><i>Returns:</i> <code>!(lhs == rhs )</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>bool operator<( const error_code & lhs, const error_code & rhs );</pre>
<blockquote>
<p><i>Returns:</i> <code>lhs.category() < rhs.category()<br>
|| (lhs.category() == rhs.category() && lhs.value() < rhs.value())</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>bool operator<( const error_condition & lhs, const error_condition & rhs );</pre>
<blockquote>
<p><i>Returns:</i> <code>lhs.category() < rhs.category()<br>
|| (lhs.category() == rhs.category() && lhs.value() < rhs.value())</code>.</p>
<p><i>Throws: </i>Nothing.</p>
</blockquote>
<pre>error_code make_error_code( errc::errc_t e );</pre>
<blockquote>
<p><i>Returns:</i> <code>error_code( e, generic_category)</code>.</p>
</blockquote>
<pre>error_condition make_error_condition( errc::errc_t e );</pre>
<blockquote>
<p><i>Returns:</i> <code>error_condition( static_cast<int>( e ), generic_category)</code>.</p>
</blockquote>
<pre>template <class charT, class traits>
std::basic_ostream<charT,traits>&
operator<<( basic_ostream<charT,traits>& os, const error_code & ec );</pre>
<blockquote>
<p><i>Effects:</i> <code>os << ec.category().name() << ':' << ec.value()</code>.</p>
<p><i>Returns:</i> <code>os</code>.</p>
</blockquote>
<pre>size_t <a name="hash_value">hash_value</a>( const error_code & ec );</pre>
<blockquote>
<p><i>Returns: </i> A hash value representing <code>ec</code>.</p>
</blockquote>
<h2><a name="Header-system_error">Header <boost/system/system_error.hpp></a></h2>
<h3><a name="Class-system_error">Class <code>
system_error</code></a></h3>
<p>The class <code>system_error</code> describes an exception object used to
report errors that have an associated <code><a href="#Class-error_code">error_code</a></code>. Such errors typically originate from operating system or other low-level
application program interfaces.</p>
<blockquote>
<pre>namespace boost
{
namespace system
{
class system_error : public std::runtime_error
{
public:
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,
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);
const error_code & code() const throw();
const char * what() const throw();
};
}
}</pre>
</blockquote>
<pre>system_error( error_code ec );</pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of class <code>system_error</code>.</p>
<p><i>Postcondition:</i> <code>code() == ec <br>
&& std::strcmp( this->runtime_error::what(), "" ) == 0</code></p>
</blockquote>
<pre>system_error( error_code ec, const char * what_arg );</pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of class <code>system_error</code>.</p>
<p><i>Postcondition:</i> <code>code() == ec <br>
&& std::strcmp( this->runtime_error::what(), what_arg ) == 0</code></p>
</blockquote>
<pre>system_error( error_code ec, const std::string & what_arg );</pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of class <code>system_error</code>.</p>
<p><i>Postcondition:</i> <code>code() == ec <br>
&& std::strcmp( this->runtime_error::what(), what_arg.c_str() ) == 0</code></p>
</blockquote>
<pre>system_error( int ev, const error_category & ecat,
const char * what_arg );</pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of class <code>system_error</code>.</p>
<p><i>Postcondition:</i> <code>code() == error_code( ev, ecat )<br>
&& std::strcmp( this->runtime_error::what(), what_arg ) == 0</code></p>
</blockquote>
<pre>system_error( int ev, const error_category & ecat,
const std::string & what_arg );</pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of class <code>system_error</code>.</p>
<p><i>Postcondition:</i> <code>code() == error_code( ev, ecat )<br>
&& std::strcmp( this->runtime_error::what(), what_arg.c_str() ) == 0</code></p>
</blockquote>
<pre>system_error( int ev, const error_category & ecat );</pre>
<blockquote>
<p><i>Effects:</i> Constructs an object of class <code>system_error</code>.</p>
<p><i>Postcondition:</i> <code>code() == error_code( ev, ecat )<br>
&& std::strcmp( this->runtime_error::what(), "" ) == 0</code></p>
</blockquote>
<pre>const error_code & code() const;</pre>
<blockquote>
<p><i>Returns:</i> <code>ec</code> or <code>error_code( ev, ecat )</code>, from
the constructor, as appropriate.</p>
</blockquote>
<pre>const char * what() const;</pre>
<blockquote>
<p><i>Returns: </i>A string incorporating <code>
this->runtime_error::what()</code> and <code>
code.message()</code>.</p>
</blockquote>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%B %d, %Y" startspan -->October 11, 2008<!--webbot bot="Timestamp" endspan i-checksum="30976" --> </font>
</p>
<p> Copyright Beman Dawes, 2006, 2007, 2008</p>
<p>Distributed under the Boost Software License, Version 1.0. See
<a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a></p>
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