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%!TEX root = std.tex
\rSec0[diagnostics]{Diagnostics library}
\rSec1[diagnostics.general]{General}
\pnum
This Clause describes components that \Cpp{} programs may use to detect and
report error conditions.
\pnum
The following subclauses describe components for
reporting several kinds of exceptional conditions,
documenting program assertions,
obtaining stacktraces, and
a global variable for error number codes,
as summarized in \tref{diagnostics.summary}.
\begin{libsumtab}{Diagnostics library summary}{diagnostics.summary}
\ref{std.exceptions} & Exception classes & \tcode{<stdexcept>} \\ \rowsep
\ref{assertions} & Assertions & \tcode{<cassert>} \\ \rowsep
\ref{errno} & Error numbers & \tcode{<cerrno>} \\ \rowsep
\ref{syserr} & System error support & \tcode{<system_error>} \\ \rowsep
\ref{stacktrace} & Stacktrace & \tcode{<stacktrace>} \\ \rowsep
\ref{debugging} & Debugging & \tcode{<debugging>} \\
\end{libsumtab}
\rSec1[std.exceptions]{Exception classes}
\rSec2[std.exceptions.general]{General}
\pnum
The \Cpp{} standard library provides classes to be used to report certain errors\iref{res.on.exception.handling} in
\Cpp{} programs.
In the error model reflected in these classes, errors are divided into two
broad categories:
\term{logic}
errors and
\term{runtime}
errors.
\pnum
The distinguishing characteristic of logic errors is that they are due to errors
in the internal logic of the program.
In theory, they are preventable.
\pnum
By contrast, runtime errors are due to events beyond the scope of the program.
They cannot be easily predicted in advance.
The header \libheaderdef{stdexcept}
defines several types of predefined exceptions for reporting errors in a \Cpp{} program.
These exceptions are related by inheritance.
\rSec2[stdexcept.syn]{Header \tcode{<stdexcept>} synopsis}
\indexlibraryglobal{logic_error}%
\indexlibraryglobal{domain_error}%
\indexlibraryglobal{invalid_argument}%
\indexlibraryglobal{length_error}%
\indexlibraryglobal{out_of_range}%
\indexlibraryglobal{runtime_error}%
\indexlibraryglobal{range_error}%
\indexlibraryglobal{overflow_error}%
\indexlibraryglobal{underflow_error}%
\begin{codeblock}
namespace std {
class logic_error;
class domain_error;
class invalid_argument;
class length_error;
class out_of_range;
class runtime_error;
class range_error;
class overflow_error;
class underflow_error;
}
\end{codeblock}
\rSec2[logic.error]{Class \tcode{logic_error}}
\indexlibraryglobal{logic_error}%
\begin{codeblock}
namespace std {
class logic_error : public exception {
public:
constexpr explicit logic_error(const string& what_arg);
constexpr explicit logic_error(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{logic_error}
defines the type of objects thrown as
exceptions to report errors presumably detectable before
the program executes, such as violations of logical preconditions or class
invariants.
\indexlibraryctor{logic_error}%
\begin{itemdecl}
constexpr logic_error(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{logic_error}%
\begin{itemdecl}
constexpr logic_error(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[domain.error]{Class \tcode{domain_error}}
\indexlibraryglobal{domain_error}%
\begin{codeblock}
namespace std {
class domain_error : public logic_error {
public:
constexpr explicit domain_error(const string& what_arg);
constexpr explicit domain_error(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{domain_error}
defines the type of objects thrown as
exceptions by the implementation to report domain errors.
\indexlibraryctor{domain_error}%
\begin{itemdecl}
constexpr domain_error(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{domain_error}%
\begin{itemdecl}
constexpr domain_error(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[invalid.argument]{Class \tcode{invalid_argument}}
\indexlibraryglobal{invalid_argument}%
\begin{codeblock}
namespace std {
class invalid_argument : public logic_error {
public:
constexpr explicit invalid_argument(const string& what_arg);
constexpr explicit invalid_argument(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{invalid_argument}
defines the type of objects thrown as exceptions to report an invalid argument.
\indexlibraryctor{invalid_argument}%
\begin{itemdecl}
constexpr invalid_argument(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{invalid_argument}%
\begin{itemdecl}
constexpr invalid_argument(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[length.error]{Class \tcode{length_error}}
\indexlibraryglobal{length_error}%
\begin{codeblock}
namespace std {
class length_error : public logic_error {
public:
constexpr explicit length_error(const string& what_arg);
constexpr explicit length_error(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{length_error}
defines the type of objects thrown as exceptions
to report an attempt to produce
an object whose length exceeds its maximum allowable size.
\indexlibraryctor{length_error}%
\begin{itemdecl}
constexpr length_error(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{length_error}%
\begin{itemdecl}
constexpr length_error(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[out.of.range]{Class \tcode{out_of_range}}
\indexlibraryglobal{out_of_range}%
\begin{codeblock}
namespace std {
class out_of_range : public logic_error {
public:
constexpr explicit out_of_range(const string& what_arg);
constexpr explicit out_of_range(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{out_of_range}
defines the type of objects thrown as exceptions to report an
argument value not in its expected range.
\indextext{argument}
\indexlibraryctor{out_of_range}%
\begin{itemdecl}
constexpr out_of_range(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{out_of_range}%
\begin{itemdecl}
constexpr out_of_range(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[runtime.error]{Class \tcode{runtime_error}}
\indexlibraryglobal{runtime_error}%
\begin{codeblock}
namespace std {
class runtime_error : public exception {
public:
constexpr explicit runtime_error(const string& what_arg);
constexpr explicit runtime_error(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{runtime_error}
defines the type of objects thrown as exceptions to report errors presumably detectable only
when the program executes.
\indexlibraryctor{runtime_error}%
\begin{itemdecl}
constexpr runtime_error(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{runtime_error}%
\begin{itemdecl}
constexpr runtime_error(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[range.error]{Class \tcode{range_error}}
\indexlibraryglobal{range_error}%
\begin{codeblock}
namespace std {
class range_error : public runtime_error {
public:
constexpr explicit range_error(const string& what_arg);
constexpr explicit range_error(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{range_error}
defines the type of objects thrown as exceptions to report range errors
in internal computations.
\indexlibraryctor{range_error}%
\begin{itemdecl}
constexpr range_error(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{range_error}%
\begin{itemdecl}
constexpr range_error(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[overflow.error]{Class \tcode{overflow_error}}
\indexlibraryglobal{overflow_error}%
\begin{codeblock}
namespace std {
class overflow_error : public runtime_error {
public:
constexpr explicit overflow_error(const string& what_arg);
constexpr explicit overflow_error(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{overflow_error}
defines the type of objects thrown as exceptions to report an arithmetic overflow error.
\indexlibraryctor{overflow_error}%
\begin{itemdecl}
constexpr overflow_error(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{overflow_error}%
\begin{itemdecl}
constexpr overflow_error(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec2[underflow.error]{Class \tcode{underflow_error}}
\indexlibraryglobal{underflow_error}%
\begin{codeblock}
namespace std {
class underflow_error : public runtime_error {
public:
constexpr explicit underflow_error(const string& what_arg);
constexpr explicit underflow_error(const char* what_arg);
};
}
\end{codeblock}
\pnum
The class
\tcode{underflow_error}
defines the type of objects thrown as exceptions to report an arithmetic underflow error.
\indexlibraryctor{underflow_error}%
\begin{itemdecl}
constexpr underflow_error(const string& what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg.c_str()) == 0}.
\end{itemdescr}
\indexlibraryctor{underflow_error}%
\begin{itemdecl}
constexpr underflow_error(const char* what_arg);
\end{itemdecl}
\begin{itemdescr}
\pnum
\ensures
\tcode{strcmp(what(), what_arg) == 0}.
\end{itemdescr}
\rSec1[assertions]{Assertions}
\rSec2[assertions.general]{General}
\pnum
The header \libheaderdef{cassert}
provides a macro for documenting \Cpp{} program assertions and a mechanism
for disabling the assertion checks through defining the macro \tcode{NDEBUG}.
\rSec2[cassert.syn]{Header \tcode{<cassert>} synopsis}
\begin{codeblock}
#define @\libmacro{assert}@(...) @\seebelow@
\end{codeblock}
\rSec2[assertions.assert]{The \tcode{assert} macro}
\pnum
If \tcode{NDEBUG} is defined as a macro name
at the point in the source file where \tcode{<cassert>} is included,
the \tcode{assert} macro is defined as
\begin{codeblock}
#define @\libmacro{assert}@(...) ((void)0)
\end{codeblock}
\pnum
Otherwise, the \libmacro{assert} macro puts a diagnostic test into programs;
it expands to an expression of type \keyword{void} which
has the following effects:
\begin{itemize}
\item
\mname{VA_ARGS} is evaluated and contextually converted to \tcode{bool}.
\item
If the evaluation yields \tcode{true} there are no further effects.
\item
Otherwise, the \tcode{assert} macro's expression
creates a diagnostic on the standard error stream (\IsoC{}, 7.23.3) in an
\impldef{format of diagnostic created by \tcode{assert} macro's expression}
format and calls \tcode{abort()}.
The diagnostic contains \tcode{\#}\mname{VA_ARGS} and
information on
the name of the source file,
the source line number, and
the name of the enclosing function
(such as provided by \tcode{source_location::current()}).
\end{itemize}
\pnum
If \mname{VA_ARGS} does not expand to
a well-formed \grammarterm{assignment-expression},
the program is ill-formed.
If such an \grammarterm{assignment-expression} is ill-formed when
treated as an unevaluated operand\iref{expr.await, expr.yield},
the program is ill-formed, no diagnostic required.
\pnum
The macro \tcode{assert} is redefined according to
the current state of \tcode{NDEBUG} each time that
\tcode{<cassert>} is included.
\pnum
An expression \tcode{assert(E)}
is a constant subexpression\iref{defns.const.subexpr}, if
\begin{itemize}
\item
\tcode{NDEBUG} is defined at the point where \tcode{assert}
is last defined or redefined, or
\item
\tcode{E} contextually converted to \tcode{bool}\iref{conv}
is a constant subexpression that evaluates to the value \tcode{true}.
\end{itemize}
\rSec1[errno]{Error numbers}
\rSec2[errno.general]{General}
\pnum
The contents of the header \libheaderdef{cerrno} are the same as the POSIX header
\libheader{errno.h}, except that \libmacro{errno} shall be defined as a macro.
\begin{note}
The intent is to remain in close alignment with the POSIX standard.
\end{note}
A separate \tcode{errno} value is provided for each thread.
\rSec2[cerrno.syn]{Header \tcode{<cerrno>} synopsis}
\begin{codeblock}
#define @\libmacro{errno}@ @\seebelow@
#define @\libmacro{E2BIG}@ @\seebelow@ // freestanding
#define @\libmacro{EACCES}@ @\seebelow@ // freestanding
#define @\libmacro{EADDRINUSE}@ @\seebelow@ // freestanding
#define @\libmacro{EADDRNOTAVAIL}@ @\seebelow@ // freestanding
#define @\libmacro{EAFNOSUPPORT}@ @\seebelow@ // freestanding
#define @\libmacro{EAGAIN}@ @\seebelow@ // freestanding
#define @\libmacro{EALREADY}@ @\seebelow@ // freestanding
#define @\libmacro{EBADF}@ @\seebelow@ // freestanding
#define @\libmacro{EBADMSG}@ @\seebelow@ // freestanding
#define @\libmacro{EBUSY}@ @\seebelow@ // freestanding
#define @\libmacro{ECANCELED}@ @\seebelow@ // freestanding
#define @\libmacro{ECHILD}@ @\seebelow@ // freestanding
#define @\libmacro{ECONNABORTED}@ @\seebelow@ // freestanding
#define @\libmacro{ECONNREFUSED}@ @\seebelow@ // freestanding
#define @\libmacro{ECONNRESET}@ @\seebelow@ // freestanding
#define @\libmacro{EDEADLK}@ @\seebelow@ // freestanding
#define @\libmacro{EDESTADDRREQ}@ @\seebelow@ // freestanding
#define @\libmacro{EDOM}@ @\seebelow@ // freestanding
#define @\libmacro{EEXIST}@ @\seebelow@ // freestanding
#define @\libmacro{EFAULT}@ @\seebelow@ // freestanding
#define @\libmacro{EFBIG}@ @\seebelow@ // freestanding
#define @\libmacro{EHOSTUNREACH}@ @\seebelow@ // freestanding
#define @\libmacro{EIDRM}@ @\seebelow@ // freestanding
#define @\libmacro{EILSEQ}@ @\seebelow@ // freestanding
#define @\libmacro{EINPROGRESS}@ @\seebelow@ // freestanding
#define @\libmacro{EINTR}@ @\seebelow@ // freestanding
#define @\libmacro{EINVAL}@ @\seebelow@ // freestanding
#define @\libmacro{EIO}@ @\seebelow@ // freestanding
#define @\libmacro{EISCONN}@ @\seebelow@ // freestanding
#define @\libmacro{EISDIR}@ @\seebelow@ // freestanding
#define @\libmacro{ELOOP}@ @\seebelow@ // freestanding
#define @\libmacro{EMFILE}@ @\seebelow@ // freestanding
#define @\libmacro{EMLINK}@ @\seebelow@ // freestanding
#define @\libmacro{EMSGSIZE}@ @\seebelow@ // freestanding
#define @\libmacro{ENAMETOOLONG}@ @\seebelow@ // freestanding
#define @\libmacro{ENETDOWN}@ @\seebelow@ // freestanding
#define @\libmacro{ENETRESET}@ @\seebelow@ // freestanding
#define @\libmacro{ENETUNREACH}@ @\seebelow@ // freestanding
#define @\libmacro{ENFILE}@ @\seebelow@ // freestanding
#define @\libmacro{ENOBUFS}@ @\seebelow@ // freestanding
#define @\libmacro{ENODEV}@ @\seebelow@ // freestanding
#define @\libmacro{ENOENT}@ @\seebelow@ // freestanding
#define @\libmacro{ENOEXEC}@ @\seebelow@ // freestanding
#define @\libmacro{ENOLCK}@ @\seebelow@ // freestanding
#define @\libmacro{ENOLINK}@ @\seebelow@ // freestanding
#define @\libmacro{ENOMEM}@ @\seebelow@ // freestanding
#define @\libmacro{ENOMSG}@ @\seebelow@ // freestanding
#define @\libmacro{ENOPROTOOPT}@ @\seebelow@ // freestanding
#define @\libmacro{ENOSPC}@ @\seebelow@ // freestanding
#define @\libmacro{ENOSYS}@ @\seebelow@ // freestanding
#define @\libmacro{ENOTCONN}@ @\seebelow@ // freestanding
#define @\libmacro{ENOTDIR}@ @\seebelow@ // freestanding
#define @\libmacro{ENOTEMPTY}@ @\seebelow@ // freestanding
#define @\libmacro{ENOTRECOVERABLE}@ @\seebelow@ // freestanding
#define @\libmacro{ENOTSOCK}@ @\seebelow@ // freestanding
#define @\libmacro{ENOTSUP}@ @\seebelow@ // freestanding
#define @\libmacro{ENOTTY}@ @\seebelow@ // freestanding
#define @\libmacro{ENXIO}@ @\seebelow@ // freestanding
#define @\libmacro{EOPNOTSUPP}@ @\seebelow@ // freestanding
#define @\libmacro{EOVERFLOW}@ @\seebelow@ // freestanding
#define @\libmacro{EOWNERDEAD}@ @\seebelow@ // freestanding
#define @\libmacro{EPERM}@ @\seebelow@ // freestanding
#define @\libmacro{EPIPE}@ @\seebelow@ // freestanding
#define @\libmacro{EPROTO}@ @\seebelow@ // freestanding
#define @\libmacro{EPROTONOSUPPORT}@ @\seebelow@ // freestanding
#define @\libmacro{EPROTOTYPE}@ @\seebelow@ // freestanding
#define @\libmacro{ERANGE}@ @\seebelow@ // freestanding
#define @\libmacro{EROFS}@ @\seebelow@ // freestanding
#define @\libmacro{ESPIPE}@ @\seebelow@ // freestanding
#define @\libmacro{ESRCH}@ @\seebelow@ // freestanding
#define @\libmacro{ETIMEDOUT}@ @\seebelow@ // freestanding
#define @\libmacro{ETXTBSY}@ @\seebelow@ // freestanding
#define @\libmacro{EWOULDBLOCK}@ @\seebelow@ // freestanding
#define @\libmacro{EXDEV}@ @\seebelow@ // freestanding
\end{codeblock}
\pnum
The meaning of the macros in this header is defined by the POSIX standard.
\xrefc{7.5}
\rSec1[syserr]{System error support}
\rSec2[syserr.general]{General}
\pnum
Subclause \ref{syserr} describes components that the standard library and
\Cpp{} programs may use to report error conditions originating from
the operating system or other low-level application program interfaces.
\pnum
Components described in \ref{syserr} do not change the value of
\tcode{errno}\iref{errno}.
\recommended
Implementations should leave the error states provided by other
libraries unchanged.
\rSec2[system.error.syn]{Header \tcode{<system_error>} synopsis}
\indexheader{system_error}%
\indexlibraryglobal{error_category}%
\indexlibraryglobal{error_code}%
\indexlibraryglobal{error_condition}%
\indexlibraryglobal{system_error}%
\begin{codeblock}
#include <compare> // see \ref{compare.syn}
namespace std {
class error_category;
const error_category& generic_category() noexcept;
const error_category& system_category() noexcept;
class error_code;
class error_condition;
class system_error;
template<class T>
struct @\libglobal{is_error_code_enum}@ : public false_type {};
template<class T>
struct @\libglobal{is_error_condition_enum}@ : public false_type {};
enum class @\libglobal{errc}@ { // freestanding
@\libmember{address_family_not_supported}{errc}@, // \tcode{EAFNOSUPPORT}
@\libmember{address_in_use}{errc}@, // \tcode{EADDRINUSE}
@\libmember{address_not_available}{errc}@, // \tcode{EADDRNOTAVAIL}
@\libmember{already_connected}{errc}@, // \tcode{EISCONN}
@\libmember{argument_list_too_long}{errc}@, // \tcode{E2BIG}
@\libmember{argument_out_of_domain}{errc}@, // \tcode{EDOM}
@\libmember{bad_address}{errc}@, // \tcode{EFAULT}
@\libmember{bad_file_descriptor}{errc}@, // \tcode{EBADF}
@\libmember{bad_message}{errc}@, // \tcode{EBADMSG}
@\libmember{broken_pipe}{errc}@, // \tcode{EPIPE}
@\libmember{connection_aborted}{errc}@, // \tcode{ECONNABORTED}
@\libmember{connection_already_in_progress}{errc}@, // \tcode{EALREADY}
@\libmember{connection_refused}{errc}@, // \tcode{ECONNREFUSED}
@\libmember{connection_reset}{errc}@, // \tcode{ECONNRESET}
@\libmember{cross_device_link}{errc}@, // \tcode{EXDEV}
@\libmember{destination_address_required}{errc}@, // \tcode{EDESTADDRREQ}
@\libmember{device_or_resource_busy}{errc}@, // \tcode{EBUSY}
@\libmember{directory_not_empty}{errc}@, // \tcode{ENOTEMPTY}
@\libmember{executable_format_error}{errc}@, // \tcode{ENOEXEC}
@\libmember{file_exists}{errc}@, // \tcode{EEXIST}
@\libmember{file_too_large}{errc}@, // \tcode{EFBIG}
@\libmember{filename_too_long}{errc}@, // \tcode{ENAMETOOLONG}
@\libmember{function_not_supported}{errc}@, // \tcode{ENOSYS}
@\libmember{host_unreachable}{errc}@, // \tcode{EHOSTUNREACH}
@\libmember{identifier_removed}{errc}@, // \tcode{EIDRM}
@\libmember{illegal_byte_sequence}{errc}@, // \tcode{EILSEQ}
@\libmember{inappropriate_io_control_operation}{errc}@, // \tcode{ENOTTY}
@\libmember{interrupted}{errc}@, // \tcode{EINTR}
@\libmember{invalid_argument}{errc}@, // \tcode{EINVAL}
@\libmember{invalid_seek}{errc}@, // \tcode{ESPIPE}
@\libmember{io_error}{errc}@, // \tcode{EIO}
@\libmember{is_a_directory}{errc}@, // \tcode{EISDIR}
@\libmember{message_size}{errc}@, // \tcode{EMSGSIZE}
@\libmember{network_down}{errc}@, // \tcode{ENETDOWN}
@\libmember{network_reset}{errc}@, // \tcode{ENETRESET}
@\libmember{network_unreachable}{errc}@, // \tcode{ENETUNREACH}
@\libmember{no_buffer_space}{errc}@, // \tcode{ENOBUFS}
@\libmember{no_child_process}{errc}@, // \tcode{ECHILD}
@\libmember{no_link}{errc}@, // \tcode{ENOLINK}
@\libmember{no_lock_available}{errc}@, // \tcode{ENOLCK}
@\libmember{no_message}{errc}@, // \tcode{ENOMSG}
@\libmember{no_protocol_option}{errc}@, // \tcode{ENOPROTOOPT}
@\libmember{no_space_on_device}{errc}@, // \tcode{ENOSPC}
@\libmember{no_such_device_or_address}{errc}@, // \tcode{ENXIO}
@\libmember{no_such_device}{errc}@, // \tcode{ENODEV}
@\libmember{no_such_file_or_directory}{errc}@, // \tcode{ENOENT}
@\libmember{no_such_process}{errc}@, // \tcode{ESRCH}
@\libmember{not_a_directory}{errc}@, // \tcode{ENOTDIR}
@\libmember{not_a_socket}{errc}@, // \tcode{ENOTSOCK}
@\libmember{not_connected}{errc}@, // \tcode{ENOTCONN}
@\libmember{not_enough_memory}{errc}@, // \tcode{ENOMEM}
@\libmember{not_supported}{errc}@, // \tcode{ENOTSUP}
@\libmember{operation_canceled}{errc}@, // \tcode{ECANCELED}
@\libmember{operation_in_progress}{errc}@, // \tcode{EINPROGRESS}
@\libmember{operation_not_permitted}{errc}@, // \tcode{EPERM}
@\libmember{operation_not_supported}{errc}@, // \tcode{EOPNOTSUPP}
@\libmember{operation_would_block}{errc}@, // \tcode{EWOULDBLOCK}
@\libmember{owner_dead}{errc}@, // \tcode{EOWNERDEAD}
@\libmember{permission_denied}{errc}@, // \tcode{EACCES}
@\libmember{protocol_error}{errc}@, // \tcode{EPROTO}
@\libmember{protocol_not_supported}{errc}@, // \tcode{EPROTONOSUPPORT}
@\libmember{read_only_file_system}{errc}@, // \tcode{EROFS}
@\libmember{resource_deadlock_would_occur}{errc}@, // \tcode{EDEADLK}
@\libmember{resource_unavailable_try_again}{errc}@, // \tcode{EAGAIN}
@\libmember{result_out_of_range}{errc}@, // \tcode{ERANGE}
@\libmember{state_not_recoverable}{errc}@, // \tcode{ENOTRECOVERABLE}
@\libmember{text_file_busy}{errc}@, // \tcode{ETXTBSY}
@\libmember{timed_out}{errc}@, // \tcode{ETIMEDOUT}
@\libmember{too_many_files_open_in_system}{errc}@, // \tcode{ENFILE}
@\libmember{too_many_files_open}{errc}@, // \tcode{EMFILE}
@\libmember{too_many_links}{errc}@, // \tcode{EMLINK}
@\libmember{too_many_symbolic_link_levels}{errc}@, // \tcode{ELOOP}
@\libmember{value_too_large}{errc}@, // \tcode{EOVERFLOW}
@\libmember{wrong_protocol_type}{errc}@, // \tcode{EPROTOTYPE}
};
template<> struct is_error_condition_enum<errc> : true_type {};
// \ref{syserr.errcode.nonmembers}, non-member functions
error_code make_error_code(errc e) noexcept;
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const error_code& ec);
// \ref{syserr.errcondition.nonmembers}, non-member functions
error_condition make_error_condition(errc e) noexcept;
// \ref{syserr.compare}, comparison operator functions
bool operator==(const error_code& lhs, const error_code& rhs) noexcept;
bool operator==(const error_code& lhs, const error_condition& rhs) noexcept;
bool operator==(const error_condition& lhs, const error_condition& rhs) noexcept;
strong_ordering operator<=>(const error_code& lhs, const error_code& rhs) noexcept;
strong_ordering operator<=>(const error_condition& lhs, const error_condition& rhs) noexcept;
// \ref{syserr.hash}, hash support
template<class T> struct hash;
template<> struct hash<error_code>;
template<> struct hash<error_condition>;
// \ref{syserr}, system error support
template<class T>
constexpr bool @\libglobal{is_error_code_enum_v}@ = is_error_code_enum<T>::value;
template<class T>
constexpr bool @\libglobal{is_error_condition_enum_v}@ = is_error_condition_enum<T>::value;
// \ref{syserr.fmt}, formatter
template<class T> struct formatter<error_code, charT>;
}
\end{codeblock}
\pnum
The value of each \tcode{enum errc} enumerator is the same as
the value of the \libheader{cerrno} macro shown in the above synopsis.
Whether or not the \libheader{system_error} implementation
exposes the \libheader{cerrno} macros is unspecified.
\pnum
The \tcode{is_error_code_enum} and \tcode{is_error_condition_enum} templates may be
specialized for program-defined types to indicate that such types are eligible
for \tcode{class error_code} and \tcode{class error_condition} implicit
conversions, respectively.
\rSec2[syserr.errcat]{Class \tcode{error_category}}
\rSec3[syserr.errcat.overview]{Overview}
\pnum
The class \tcode{error_category} 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 \tcode{error_category} to support
categories of errors in addition to those defined in this document.
Such classes shall behave as specified in subclause~\ref{syserr.errcat}.
\begin{note}
\tcode{error_category} objects are
passed by reference, and two such objects
are equal if they have the same address.
If there is more than a single object of a custom \tcode{error_category} type,
such equality comparisons can evaluate to \tcode{false}
even for objects holding the same value.
\end{note}
\indexlibraryglobal{error_category}%
\indexlibraryctor{error_category}%
\indexlibrarydtor{error_category}%
\indexlibraryglobal{generic_category}%
\indexlibraryglobal{system_category}%
\begin{codeblock}
namespace std {
class error_category {
public:
constexpr error_category() noexcept;
virtual ~error_category();
error_category(const error_category&) = delete;
error_category& operator=(const error_category&) = delete;
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 string message(int ev) const = 0;
bool operator==(const error_category& rhs) const noexcept;
strong_ordering operator<=>(const error_category& rhs) const noexcept;
};
const error_category& generic_category() noexcept;
const error_category& system_category() noexcept;
}
\end{codeblock}
\rSec3[syserr.errcat.virtuals]{Virtual members}
\indexlibrarymember{name}{error_category}%
\begin{itemdecl}
virtual const char* name() const noexcept = 0;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
A string in the ordinary literal encoding naming the error category.
\end{itemdescr}
\indexlibrarymember{default_error_condition}{error_category}%
\begin{itemdecl}
virtual error_condition default_error_condition(int ev) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{error_condition(ev, *this)}.
\end{itemdescr}
\indexlibrarymember{equivalent}{error_category}%
\begin{itemdecl}
virtual bool equivalent(int code, const error_condition& condition) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{default_error_condition(code) == condition}.
\end{itemdescr}
\indexlibrarymember{equivalent}{error_category}%
\begin{itemdecl}
virtual bool equivalent(const error_code& code, int condition) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{*this == code.category() \&\& code.value() == condition}.
\end{itemdescr}
\indexlibrarymember{message}{error_category}%
\begin{itemdecl}
virtual string message(int ev) const = 0;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
A string of multibyte characters in the execution character set
that describes the error condition denoted by \tcode{ev}.
\end{itemdescr}
\rSec3[syserr.errcat.nonvirtuals]{Non-virtual members}
\indexlibrarymember{operator==}{error_category}%
\begin{itemdecl}
bool operator==(const error_category& rhs) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{this == \&rhs}.
\end{itemdescr}
\indexlibrarymember{operator<=>}{error_category}%
\begin{itemdecl}
strong_ordering operator<=>(const error_category& rhs) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{compare_three_way()(this, \&rhs)}.
\begin{note}
\tcode{compare_three_way}\iref{comparisons.three.way} provides a total ordering for pointers.
\end{note}
\end{itemdescr}
\rSec3[syserr.errcat.derived]{Program-defined classes derived from \tcode{error_category}}
\indexlibrarymember{name}{error_category}%
\begin{itemdecl}
virtual const char* name() const noexcept = 0;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
A string naming the error category.
\end{itemdescr}
\indexlibrarymember{default_error_condition}{error_category}%
\begin{itemdecl}
virtual error_condition default_error_condition(int ev) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
An object of type \tcode{error_condition} that corresponds to \tcode{ev}.
\end{itemdescr}
\indexlibrarymember{equivalent}{error_category}%
\begin{itemdecl}
virtual bool equivalent(int code, const error_condition& condition) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{true} if, for the category of error represented by \tcode{*this}, \tcode{code} is considered equivalent to \tcode{condition}; otherwise, \tcode{false}.
\end{itemdescr}
\indexlibrarymember{equivalent}{error_category}%
\begin{itemdecl}
virtual bool equivalent(const error_code& code, int condition) const noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{true} if, for the category of error represented by \tcode{*this}, \tcode{code} is considered equivalent to \tcode{condition}; otherwise, \tcode{false}.
\end{itemdescr}
\rSec3[syserr.errcat.objects]{Error category objects}
\indexlibraryglobal{generic_category}%
\begin{itemdecl}
const error_category& generic_category() noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
A reference to an object of a type derived from class \tcode{error_category}.
All calls to this function shall return references to the same object.
\pnum
\remarks
The object's \tcode{default_error_condition} and \tcode{equivalent} virtual functions shall behave as specified for the class \tcode{error_category}. The object's \tcode{name} virtual function shall return a pointer to the string \tcode{"generic"}.
\end{itemdescr}
\indexlibraryglobal{system_category}%
\begin{itemdecl}
const error_category& system_category() noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
A reference to an object of a type derived from class \tcode{error_category}.
All calls to this function shall return references to the same object.
\pnum
\remarks
The object's \tcode{equivalent} virtual functions shall behave as specified for
class \tcode{error_category}. The object's \tcode{name} virtual function shall return a
pointer to the string \tcode{"system"}. The object's \tcode{default_error_condition}
virtual function shall behave as follows:
If the argument \tcode{ev} is equal to 0,