Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
As constexpr will not be supported
by some compilers, it is replaced in the code by BOOST_CHRONO_CONSTEXPR for
constexpr functions and BOOST_CHRONO_STATIC_CONSTEXPR for struct/class static
fields. The same applies to noexecpt
which is replaced by BOOST_CHRONO_NOEXCEPT in the code.
The documentation doesn't use these macros.
Include all the chrono header files.
#include <boost/chrono/chrono.hpp> #include <boost/chrono/chrono_io.hpp> #include <boost/chrono/process_cpu_clocks.hpp> #include <boost/chrono/thread_clocks.hpp> #include <boost/chrono/ceil.hpp> #include <boost/chrono/floor.hpp> #include <boost/chrono/round.hpp>
<boost/chrono.hpp><boost/chrono.hpp><boost/chrono/duration.hpp>Clock
RequirementsTrivialClock RequirementsEcClock
Requirements<boost/chrono/time_point.hpp><boost/chrono/system_clocks.hpp><boost/chrono/clock_strings.hpp><boost/chrono/typeof/boost/chrono/chrono.hpp>Include only the standard files.
#include <boost/chrono/duration.hpp> #include <boost/chrono/time_point.hpp> #include <boost/chrono/system_clocks.hpp> #include <boost/chrono/typeof/boost/chrono/chrono.hpp>
Next follows some limitation respect to the C++0x recomendations:
The current implementation provides in addition:
When BOOST_NO_STATIC_ASSERT
is defined, the user can select the way static assertions are reported.
Define
BOOST_CHRONO_USES_STATIC_ASSERT:
define it if you want to use Boost.StaticAssert.
BOOST_CHRONO_USES_MPL_ASSERT:
define it if you want to use Boost.MPL static asertions.
BOOST_CHRONO_USES_ARRAY_ASSERT:
define it if you want to use internal static asertions.
The default behavior is as BOOST_CHRONO_USES_ARRAY_ASSERT
was defined.
When BOOST_CHRONO_USES_MPL_ASSERT
is not defined the following symbols are defined as
#define BOOST_CHRONO_A_DURATION_REPRESENTATION_CAN_NOT_BE_A_DURATION \ "A duration representation can not be a duration" #define BOOST_CHRONO_SECOND_TEMPLATE_PARAMETER_OF_DURATION_MUST_BE_A_STD_RATIO \ "Second template parameter of duration must be a boost::ratio" #define BOOST_CHRONO_DURATION_PERIOD_MUST_BE_POSITIVE \ "duration period must be positive" #define BOOST_CHRONO_SECOND_TEMPLATE_PARAMETER_OF_TIME_POINT_MUST_BE_A_BOOST_CHRONO_DURATION \ "Second template parameter of time_point must be a boost::chrono::duration"
Depending on the static assertion used system you will have an hint of the failing assertion either through the symbol or through the text.
When BOOST_CHRONO_DONT_PROVIDE_HYBRID_ERROR_HANDLING
is defined the lib don't provides the hybrid error handling prototypes:
Clock::time_point Clock::now(system::error_code&ec=boost::thows());
This allow to be closer to the standard and to avoid the Boost.System dependency, making possible to have Boost.Chrono as a header-only library.
When BOOST_CHRONO_HEADER_ONLY
is defined the lib is header-only.
If in addition BOOST_USE_WINDOWS_H
is defined <windows.h> is included, otherwise files in
boost/detail/win are used to reduce the impact
of including <windows.h>.
However, you will either need to define BOOST_CHRONO_DONT_PROVIDE_HYBRID_ERROR_HANDLING
or link with Boost.System.
This file contains duration specific classes and non-member functions.
namespace boost { namespace chrono { template <class Rep, class Period =ratio<1> > classduration; } template <class Rep1, class Period1, class Rep2, class Period2> structcommon_type<duration<Rep1, Period1>, duration<Rep2, Period2> >; namespace chrono { // customization traits template <class Rep> structtreat_as_floating_point; template <class Rep> structduration_values; // duration arithmetic template <class Rep1, class Period1, class Rep2, class Period2> constexpr typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2> >::typeoperator+( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period1, class Rep2, class Period2> constexpr typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2> >::typeoperator-( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period, class Rep2> constexpr duration<typename common_type<Rep1, Rep2>::type, Period>operator*( const duration<Rep1, Period>& d, const Rep2& s); template <class Rep1, class Period, class Rep2> constexpr duration<typename common_type<Rep1, Rep2>::type, Period>operator*( const Rep1& s, const duration<Rep2, Period>& d); template <class Rep1, class Period, class Rep2> constexpr duration<typename common_type<Rep1, Rep2>::type, Period>operator/( const duration<Rep1, Period>& d, const Rep2& s); template <class Rep1, class Period1, class Rep2, class Period2> constexpr typename common_type<Rep1, Rep2>::typeoperator/( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); #ifdef BOOST_CHRONO_EXTENSIONS // Used to get frecuency of events template <class Rep1, class Rep2, class Period> constexpr doubleoperator/( const Rep1& s, const duration<Rep2, Period>& d); #endif // duration comparisons template <class Rep1, class Period1, class Rep2, class Period2> constexpr booloperator==( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period1, class Rep2, class Period2> constexpr booloperator!=( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period1, class Rep2, class Period2> constexpr bool __duration__op_le_1( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period1, class Rep2, class Period2> constexpr booloperator<=( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period1, class Rep2, class Period2> constexpr booloperator>( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period1, class Rep2, class Period2> constexpr booloperator>=( const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); // duration_cast template <class ToDuration, class Rep, class Period> constexpr ToDurationduration_cast(const duration<Rep, Period>& d); // convenience typedefs typedef duration<boost::int_least64_t, nano>nanoseconds; // at least 64 bits needed typedef duration<boost::int_least64_t, micro>microseconds; // at least 55 bits needed typedef duration<boost::int_least64_t, milli>milliseconds; // at least 45 bits needed typedef duration<boost::int_least64_t>seconds; // at least 35 bits needed typedef duration<boost::int_least32_t, ratio< 60> >minutes; // at least 29 bits needed typedef duration<boost::int_least32_t, ratio<3600> >hours; // at least 23 bits needed } }
template <class Rep> struct treat_as_floating_point : boost::is_floating_point<Rep> {};
The duration template uses the
treat_as_floating_point trait
to help determine if a duration with one tick period
can be converted to another duration with a different
tick period. If treat_as_floating_point<Rep>::value
is true, then Rep is a floating-point type and
implicit conversions are allowed among durations. Otherwise, the
implicit convertibility depends on the tick periods of the durations. If Rep is a class type which emulates
a floating-point type, the author of Rep
can specialize treat_as_floating_point so
that duration will treat this
Rep as if it were a
floating-point type. Otherwise Rep
is assumed to be an integral type, or a class emulating an integral
type.
template <class Rep> struct duration_values { public: static constexpr Repzero(); static constexpr Repmax(); static constexpr Repmin(); };
The duration template uses the
duration_values trait to construct
special values of the duration's representation
(Rep). This is done
because the representation might be a class type with behavior which
requires some other implementation to return these special values.
In that case, the author of that class type should specialize duration_values to return
the indicated values.
static constexpr Rep zero();
Returns: Rep(0). Note:
Rep(0)
is specified instead of Rep() since Rep() may have some other meaning, such
as an uninitialized value.
Remarks: The value returned corresponds to the additive identity.
static constexpr Rep max();
Returns: numeric_limits<Rep>::max().
Remarks: The value returned compares greater than zero().
static constexpr Rep min();
Returns: numeric_limits<Rep>::lowest().
Remarks: The value returned compares
less than or equal to zero().
template <class Rep1, class Period1, class Rep2, class Period2> structcommon_type<chrono::duration<Rep1, Period1>, chrono::duration<Rep2, Period2> > { typedef chrono::duration<typenamecommon_type<Rep1, Rep2>::type, see bellow> type; };
The period of the duration indicated by this specialization
of common_type is the
greatest common divisor of Period1
and Period2. This can
be computed by forming a ratio
of the greatest common divisor of Period1::num
and Period2::num, and the least common multiple
of Period1::den and Period2::den.
Note: The typedef type is the duration with the largest tick
period possible where both duration arguments will convert
to it without requiring a division operation. The representation of this
type is intended to be able to hold any value resulting from this conversion,
with the possible exception of round-off error when floating-point durations are involved (but
not truncation error).
A duration measures time between
two points in time (time_point). A duration has a representation
which holds a count of ticks, and a tick period. The tick period is the
amount of time which occurs from one tick to another in units of a second.
It is expressed as a rational constant using ratio.
namespace boost { namespace chrono { template <class Rep, class Period> class duration { public: typedef Rep rep; typedef Period period; private: rep rep_; // exposition only public: constexprduration(); template <class Rep2> constexpr explicitduration(const Rep2& r); template <class Rep2, class Period2> constexprduration(const duration<Rep2, Period2>& d); duration& operator=(const duration&) = default; constexpr repcount() const; constexpr duration __duration__op_plus(); constexpr duration __duration__op_minus(); duration&operator++(); durationoperator++(int); duration&operator--(); durationoperator--(int); duration&operator+=(const duration& d); duration&operator-=(const duration& d); duration&operator*==(const rep& rhs); duration&operator/=(const rep& rhs); duration&operator%=(const rep& rhs); duration&operator%=(const duration& rhs); static constexpr durationzero(); static constexpr durationmin(); static constexpr durationmax(); }; }}
Rep must be an arithmetic
type, or a class emulating an arithmetic type, compile diagnostic otherwise.
If duration is instantiated with
the type of Rep being
a duration, compile diagnostic
is issued.
Period must be an instantiation
of ratio, compile diagnostic
otherwise.
Period::num must be positive, compile diagnostic
otherwise.
Examples:
The following members of duration do not throw an exception
unless the indicated operations on the representations throw an exception.
constexpr duration();
Effects: Constructs an object of type
duration from duration_values<rep>::zero().
template <class Rep2> constexpr explicit duration(const Rep2& r);
Remarks: Rep2
is implicitly convertible to rep,
and
treat_as_floating_point<rep>::value
is true, or
!treat_as_floating_point<rep>::value
&& !treat_as_floating_point<Rep2>::value is true.
If these constraints are not met, this constructor will not participate
in overload resolution. Note: This
requirement prevents construction of an integral-based duration with a floating-point
representation. Such a construction could easily lead to confusion
about the value of the duration.
Example:
duration<int, milli> d(3.5); // do not compileduration<int, milli> d(3); // ok
Effects: Constructs an object of type
duration.
PostConditions: count() == static_cast<rep>(r).
template <class Rep2, class Period2> constexprduration(constduration<Rep2, Period2>& d);
Remarks: treat_as_floating_point<rep>::value,
or ratio_divide<Period2,
period>::type::den ==
1, else this constructor will
not participate in overload resolution. note
This requirement prevents implicit truncation error when converting
between integral-based durations. Such a construction
could easily lead to confusion about the value of the duration.
Example:
duration<int, milli> ms(3);duration<int, micro> us = ms; // okduration<int, milli> ms2 = us; // do not compile
Effects: Constructs an object of type
duration, constructing rep_ from duration_cast<.
duration>(d).count()
static constexpr duration zero();
Returns: duration(duration_values<rep>::zero())
static constexpr duration min();
Returns: duration(duration_values<rep>::min()).
static constexpr duration max();
Returns: duration(duration_values<rep>::max())
template <class Rep1, class Period1, class Rep2, class Period2> constexpr typenamecommon_type<duration<Rep1, Period1>,duration<Rep2, Period2> >::type operator+(constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Returns: CD(CD(lhs).count() + CD(rhs).count())
where CD is the type
of the return value.
template <class Rep1, class Period1, class Rep2, class Period2> constexpr typenamecommon_type<duration<Rep1, Period1>,duration<Rep2, Period2> >::type operator-(constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Returns: CD(CD(lhs).count() - CD(rhs).count())
where CD is the type
of the return value.
template <class Rep1, class Period, class Rep2> constexprduration<typenamecommon_type<Rep1, Rep2>::type, Period> operator*(constduration<Rep1, Period>& d, const Rep2& s);
Requires: Let CR
represent the common_type
of Rep1 and Rep2. This function will not participate
in overload resolution unless both Rep1
and Rep2 are implicitly
convertible to CR.
Returns: CD(CD(d).count() * s)
where CD is the type
of the return value.
template <class Rep1, class Period, class Rep2> constexprduration<typenamecommon_type<Rep1, Rep2>::type, Period> operator*(const Rep1& s, constduration<Rep2, Period>& d);
Requires: Let CR
represent the common_type
of Rep1 and Rep2. This function will not participate
in overload resolution unless both Rep1
and Rep2 are implicitly
convertible to CR.
Returns: d
* s.
template <class Rep1, class Period, class Rep2> constexprduration<typenamecommon_type<Rep1, Rep2>::type, Period> operator/(constduration<Rep1, Period>& d, const Rep2& s);
Requires: Let CR
represent the common_type
of Rep1 and Rep2. This function will not participate
in overload resolution unless both Rep1
and Rep2 are implicitly
convertible to CR,
and Rep2 is not an
instantiation of duration.
Returns: CD(CD(d).count() / s)
where CD is the type
of the return value.
template <class Rep1, class Period1, class Rep2, class Period2> constexpr typenamecommon_type<Rep1, Rep2>::type operator/(constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Remarks: Let CD
represent the common_type
of the two duration arguments. Returns: Returns CD(lhs).count() / CD(rhs).count().
Included only if BOOST_CHRONO_EXTENSIONS is defined.
This overloading could be used to get the frequency of an event counted
by Rep1.
template <class Rep1, class Rep2, class Period>
constexpr
double operator/(const Rep1& s, const duration<Rep2, Period>& d);
Remarks: Let CR
represent the common_type
of Rep1 and Rep2. This function will not participate
in overload resolution unless both Rep1
and Rep2 are implicitly
convertible to CR,
and Rep1 is not an
instantiation of duration. Let CD represent duration<CR,Period>.
Returns: CR(s)/CD(d).count() where CD
is the type of the return value.
template <class Rep1, class Period, class Rep2> constexprduration<typenamecommon_type<Rep1, Rep2>::type, Period> operator%(constduration<Rep1, Period>& d, const Rep2& s);
Remarks: Let CR
represent the common_type
of Rep1 and Rep2. This function will not participate
in overload resolution unless Rep2 must be implicitly convertible to
CR and Rep2 must not be an instantiation of duration.
Returns: CD(CD(d).count() % s) where
CD is the type of the
return value.
template <class Rep1, class Period1, class Rep2, class Period2> constexpr typenamecommon_type<duration<Rep1, Period1>,duration<Rep2, Period2> >::type operator%(constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Remarks: This function will not participate in overload resolution unless
Returns: CD(CD(lhs).count() % CD(rhs).count())
where CD is the type
of the return value.
template <class Rep1, class Period1, class Rep2, class Period2> bool operator==(constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Returns: Let CD
represent the common_type
of the two duration arguments.
Returns: Returns CD(lhs).count() == CD(rhs).count()
template <class Rep1, class Period1, class Rep2, class Period2> bool operator!=(constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Returns: !(lhs ==
rhs).
template <class Rep1, class Period1, class Rep2, class Period2> bool operator< (constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Returns: Let CD
represent the common_type
of the two duration arguments. Returns
CD(lhs).count()
< CD(rhs).count()
template <class Rep1, class Period1, class Rep2, class Period2> bool operator<=(constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Returns: !(rhs <
lhs).
template <class Rep1, class Period1, class Rep2, class Period2> bool operator> (constduration<Rep1, Period1>& lhs, constduration<Rep2, Period2>& rhs);
Returns: rhs
< lhs.
template <classToDuration, class Rep, class Period>ToDurationduration_cast(constduration<Rep, Period>& d);
Requires: This function will not participate
in overload resolution unless ToDuration
is an instantiation of duration.
Returns: Forms CF
which is a ratio resulting
from ratio_divide<Period, typename ToDuration::period>::type.
Let CR be the common_type of ToDuration::rep,
Rep, and intmax_t.
CF::num ==
1 and CF::den
== 1,
then returns ToDuration(static_cast<typename
ToDuration::rep>(d.count()))
CF::num !=
1 and CF::den
== 1,
then returns ToDuration(static_cast<typename
ToDuration::rep>(static_cast<CR>(d.count())
* static_cast<CR>(CF::num)))
CF::num ==
1 and CF::den
!= 1,
then returns ToDuration(static_cast<typename
ToDuration::rep>(static_cast<CR>(d.count())
/ static_cast<CR>(CF::den)))
ToDuration(static_cast<typename
ToDuration::rep>(static_cast<CR>(d.count())
* static_cast<CR>(CF::num) / static_cast<CR>(CF::den)))
Remarks: This function does not rely
on any implicit conversions. All conversions must be accomplished through
static_cast. The implementation
avoids all multiplications or divisions when it is known at compile-time
that it can be avoided because one or more arguments are 1. All intermediate computations are carried
out in the widest possible representation and only converted to the destination
representation at the final step.
// convenience typedefs typedefduration<boost::int_least64_t, nano> nanoseconds; // at least 64 bits needed typedefduration<boost::int_least64_t, micro> microseconds; // at least 55 bits needed typedefduration<boost::int_least64_t, milli> milliseconds; // at least 45 bits needed typedefduration<boost::int_least64_t> seconds; // at least 35 bits needed typedefduration<boost::int_least32_t,ratio< 60> > minutes; // at least 29 bits needed typedefduration<boost::int_least32_t,ratio<3600> > hours; // at least 23 bits needed
A clock represents a bundle consisting of a duration, a time_point, and a function now()
to get the current time_point. A clock must meet
the requirements in the following Table.
In this table C1 and C2 denote Clock
types. t1 and t2 are values returned from C1::now()
where the call returning t1
happens before the call returning t2
and both of these calls occur before C1::time_point::max(). (note This means C1 did not wrap around
between t1 and t2.).
Table 4.1. Clock Requirements
|
expression |
return type |
operational semantics |
|---|---|---|
|
|
An arithmetic type or class emulating an arithmetic type. |
The representation type of the |
|
|
|
The tick period of the clock in seconds. |
|
|
|
The |
|
|
|
The |
|
|
|
|
|
|
|
Returns a |
Models of Clock:
A type TC meets the TrivialClock requirements if:
TC satisfies the Clock requirements,
TC::rep, TC::duration,
and TC::time_point satisfy the requirements
of EqualityComparable,
LessThanComparable,
DefaultConstructible,
CopyConstructible,
CopyAssignable, Destructible, and the requirements
of numeric types.
![[Note]](../../../doc/src/images/note.png) |
Note |
|---|---|
This means, in particular, that operations on these types will not throw exceptions. |
TC::rep,
TC::duration, and TC::time_point
are swappable,
TC::now()
does not throw exceptions, and
TC::time_point::clock meets the TrivialClock
requirements, recursively.
Models of TrivialClock:
A type EcC meets the EcClock requirements if
TC satisfies the TrivialClock requirements, and
now()
interfaces allowing to recover internal error codes as described in
the following table.
In this table C1 denotes
a EcClock type and ec is an instance of a boost::system::error_code.
Table 4.2. Clock Requirements
|
expression |
return type |
operational semantics |
|---|---|---|
|
|
|
Returns a |
|
|
|
Returns a |
Models of Clock:
This file contains time_point specific classes and
non-member functions.
namespace boost { namespace chrono { template <classClock, classDuration= typename Clock::duration> classtime_point; } template <classClock, classDuration1, classDuration2> structcommon_type<time_point<Clock, Duration1>, time_point<Clock, Duration2> >; namespace chrono { // time_point arithmetic template <classClock, classDuration1, class Rep2, class Period2> constexpr time_point<Clock, typename common_type<Duration1, duration<Rep2, Period2> >::type>operator+(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs); template <class Rep1, class Period1, classClock, classDuration2> constexpr time_point<Clock, typename common_type<duration<Rep1, Period1>, Duration2>::type>operator+(const duration<Rep1, Period1>& lhs, const time_point<Clock, Duration2>& rhs); template <classClock, classDuration1, class Rep2, class Period2> constexpr time_point<Clock, typename common_type<Duration1, duration<Rep2, Period2> >::type>operator-(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs); template <classClock, classDuration1, classDuration2> constexpr typename common_type<Duration1, Duration2>::typeoperator-(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); // time_point comparisons template <classClock, classDuration1, classDuration2> constexpr booloperator==(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); template <classClock, classDuration1, classDuration2> constexpr booloperator!=(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); template <classClock, classDuration1, classDuration2> constexpr booloperator<(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); template <classClock, classDuration1, classDuration2> constexpr booloperator<=(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); template <classClock, classDuration1, classDuration2> constexpr booloperator>(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); template <classClock, classDuration1, classDuration2> constexpr booloperator>=(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); // time_point_cast template <classToDuration, classClock, classDuration> constexpr time_point<Clock, ToDuration>time_point_cast(const time_point<Clock, Duration>& t); } }
template <classClock, classDuration1, classDuration2> structcommon_type<chrono::time_point<Clock,Duration1>, chrono::time_point<Clock,Duration2> > { typedef chrono::time_point<Clock, typenamecommon_type<Duration1,Duration2>::type> type; };
The common_type of two
time_points is a time_point with the same Clock
(both have the same Clock), and the common_type of the two durations.
A time_point represents a point
in time with respect to a specific clock.
template <classClock, classDuration> class time_point { public: typedef Clock clock; typedef Duration duration; typedef typename duration::rep rep; typedef typename duration::period period; private: duration d_; // exposition only public: constexprtime_point(); constexpr explicittime_point(const duration& d); // conversions template <classDuration2> constexprtime_point(const time_point<clock,Duration2>& t); // observer constexpr durationtime_since_epoch() const; // arithmetic #ifdef BOOST_CHRONO_EXTENSIONS constexpr time_pointoperator+(); constexpr time_pointoperator-(); time_point&operator++(); time_pointoperator++(int); time_point&operator--(); time_pointoperator--(int); time_point& __time_point__op_plus_eq_1(const rep& d); time_point&operator-=(const rep& d); #endif time_point& __time_point__op_plus_eq_2(const duration& d); time_point&operator-=(const duration& d); // special values static constexpr time_pointmin(); static constexpr time_pointmax(); };
Clock must meet the Clock requirements.
Duration must be an instantiation of duration, compile diagnostic
otherwise.
constexpr time_point();
Effects: Constructs an object of
time_point, initializing
d_ with duration::zero().
This time_point represents the
epoch.
constexpr time_point(const duration& d);
Effects: Constructs an object of
time_point, initializing
d_ with d. This time_point represents the
epoch + d.
template <classDuration2> constexpr time_point(consttime_point<clock,Duration2>& t);
Requires: This function will not participate
in overload resolution unless Duration2
is implicitly convertible to duration.
Effects: Constructs an object of
time_point, initializing
d_ with t.time_since_epoch().
time_point& operator+=(const duration& d);
Effects: d_
+= d.
Returns: *this.
time_point& operator-=(const duration& d);
Effects: d_
-= d
Returns: *this.
template <classClock, classDuration1, class Rep2, class Period2> constexprtime_point<Clock, typenamecommon_type<Duration1, duration<Rep2, Period2> >::type> operator+(consttime_point<Clock,Duration1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CT(lhs.time_since_epoch() + rhs)
where CT is the type
of the return value.
template <class Rep1, class Period1, classClock, classDuration2> constexprtime_point<Clock, typenamecommon_type<duration<Rep1, Period1>,Duration2>::type> operator+(const duration<Rep1, Period1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: rhs
+ lhs.
template <classClock, classDuration1, class Rep2, class Period2> constexprtime_point<Clock, typenamecommon_type<Duration1, duration<Rep2, Period2> >::type> operator-(consttime_point<Clock,Duration1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: lhs
+ (-rhs).
template <classClock, classDuration1, classDuration2> constexpr typenamecommon_type<Duration1,Duration2>::type operator-(consttime_point<Clock,Duration1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: lhs.time_since_epoch() - rhs.time_since_epoch().
template <classClock, classDuration1, classDuration2> constexpr bool operator==(consttime_point<Clock,Duration1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: lhs.time_since_epoch() == rhs.time_since_epoch().
template <classClock, classDuration1, classDuration2> constexpr bool operator!=(consttime_point<Clock,Duration1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: !(lhs ==
rhs).
template <classClock, classDuration1, classDuration2> constexpr bool operator< (consttime_point<Clock,Duration1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: lhs.time_since_epoch() < rhs.time_since_epoch().
template <classClock, classDuration1, classDuration2> constexpr bool operator<=(consttime_point<Clock,Duration1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: !(rhs <
lhs).
template <classClock, classDuration1, classDuration2> constexpr bool operator>(consttime_point<Clock,Duration1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: rhs
< lhs.
template <classClock, classDuration1, classDuration2> constexpr bool operator>=(consttime_point<Clock,Duration1>& lhs, consttime_point<Clock,Duration2>& rhs);
Returns: !(lhs <
rhs).
template <classToDuration, classClock, classDuration> constexprtime_point<Clock, ToDuration>time_point_cast(consttime_point<Clock,Duration>& t);
Requires: This function will not participate
in overload resolution unless ToDuration
is an instantiation of duration.
Returns: time_point<Clock, ToDuration>(duration_cast<ToDuration>(t.time_since_epoch()))
This file contains the standard clock classes. The types defined in this
section satisfy the TrivialClock requirements
namespace boost { namespace chrono { // Clocks classsystem_clock; classsteady_clock; classhigh_resolution_clock; template <class CharT> struct clock_string<system_clock, CharT>; template <class CharT> struct clock_string<steady_clock, CharT>; } }
The system_clock class provides
a means of obtaining the current wall-clock time from the system-wide
real-time clock. The current time can be obtained by calling system_clock::now().
Instances of system_clock::time_point
can be converted to and from time_t with the system_clock::to_time_t() and system_clock::to_time_point() functions. If system clock is not steady,
a subsequent call to system_clock::now() may return an earlier time than a previous
call (e.g. if the operating system clock is manually adjusted, or synchronized
with an external clock).
The current implementation of system_clock is related an epoch
(midnight UTC of January 1, 1970), but this is not in the contract. You
need to use the static function static
std::time_t to_time_t(const time_point& t);
which returns a time_t
type that is based on midnight UTC of January 1, 1970.
class system_clock {
public:
typedef see bellow duration;
typedef duration::rep rep;
typedef duration::period period;
typedef chrono::time_point<system_clock> time_point;
static constexpr bool is_steady = false;
static time_point now() noexcept;
static time_point now(system::error_code & ec);
// Map to C API
static std::time_t to_time_t(const time_point& t) noexcept;
static time_point from_time_t(std::time_t t) noexcept;
};
system_clock satisfy the Clock
requirements:
system_clock::duration::min()
< system_clock::duration::zero() is true.
duration
typedef has a resolution that depends on the one provided by the
platform.
time_t to_time_t(const time_point& t) noexcept;
Returns: A time_t
such that the time_t
and t represent the
same point in time, truncated to the coarser of the precisions among
time_t and time_point.
time_point from_time_t(time_t t) noexcept;
Returns: A time_point such that the
time_point and t represent the same point in time,
truncated to the coarser of the precisions among time_point and time_t.
Defined if the platform support steady clocks.
steady_clock satisfy the Clock
requirements.
steady_clock class provides
access to the system-wide steady clock. The current time can be obtained
by calling steady_clock::now(). There is no fixed relationship between
values returned by steady_clock::now() and wall-clock time.
#ifdef BOOST_HAS_CLOCK_STEADY class steady_clock { public: typedefnanosecondsduration; typedef duration::rep rep; typedef duration::period period; typedef chrono::time_point<steady_clock> time_point; static constexpr bool is_steady = true; static time_point now() noexcept; static time_point now(system::error_code & ec); }; #endif
high_resolution_clock satisfy
the Clock
requirements.
#ifdefBOOST_CHRONO_HAS_CLOCK_STEADYtypedefsteady_clockhigh_resolution_clock; // as permitted by [time.clock.hires] #else typedefsystem_clockhigh_resolution_clock; // as permitted by [time.clock.hires] #endif
template <class CharT> struct clock_string<system_clock, CharT> { static std::basic_string<CharT> name(); static std::basic_string<CharT> since(); };
clock_string<>::name()
returns "system_clock".
clock_string<>::since()
returns " since Jan 1, 1970"
#ifdef BOOST_CHRONO_HAS_CLOCK_STEADY template <class CharT> struct clock_string<steady_clock, CharT> { static std::basic_string<CharT> name(); static std::basic_string<CharT> since(); }; #endif
clock_string<>::name()
returns "steady_clock".
clock_string<>::since()
returns " since boot"
namespace boost {
namespace chrono {
template <class Clock, class CharT>
struct clock_string;
}
}
template <class Clock, class CharT>
struct clock_string;
This template must be specialized for specific clocks. The specialization must define the following functions
static std::basic_string<CharT> name(); static std::basic_string<CharT> since();
clock_string<>::name()
return the clock name, which usually corresponds to the class name.
clock_string<>::since()
return the textual format of the clock epoch.
Register duration<>
and time_point<>
class templates to Boost.Typeof.
namespace boost { namespace chrono { template <class CharT> class duration_punct; template <class CharT, class Traits> std::basic_ostream<CharT, Traits>& duration_short(std::basic_ostream<CharT, Traits>& os); template <class CharT, class Traits> std::basic_ostream<CharT, Traits>& duration_long(std::basic_ostream<CharT, Traits>& os); template <class CharT, class Traits, class Rep, class Period> std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const duration<Rep, Period>& d); template <class CharT, class Traits, class Rep, class Period> std::basic_istream<CharT, Traits>& operator>>(std::basic_istream<CharT, Traits>& is, duration<Rep, Period>& d) template <class CharT, class Traits, class Clock, class Duration> std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const time_point<Clock, Duration>& tp); template <class CharT, class Traits, class Clock, class Duration> std::basic_istream<CharT, Traits>& operator>>(std::basic_istream<CharT, Traits>& is, time_point<Clock, Duration>& tp); } }
The duration unit names can be customized
through the facet: duration_punct. duration unit names come in
two varieties: long and short. The default constructed duration_punct provides names
in the long format. These names are English descriptions. Other languages
are supported by constructing a duration_punct with the proper
spellings for "hours", "minutes" and "seconds",
and their abbreviations (for the short format).
template <class CharT> class duration_punct : public std::locale::facet { public: typedef std::basic_string<CharT> string_type; enum {use_long, use_short}; static std::locale::id id; explicit duration_punct(int use = use_long); duration_punct(int use, const string_type& long_seconds, const string_type& long_minutes, const string_type& long_hours, const string_type& short_seconds, const string_type& short_minutes, const string_type& short_hours); duration_punct(int use, const duration_punct& d); template <class Period> string_type short_name() const; template <class Period> string_type long_name() const; template <class Period> string_type name() const; bool is_short_name() const; bool is_long_name() const; };
The short or long format can be easily chosen by streaming a duration_short or duration_long
manipulator respectively.
template <class CharT, class Traits> std::basic_ostream<CharT, Traits>& duration_short(std::basic_ostream<CharT, Traits>& os);
Effects: Set the duration_punct facet to stream
durations and time_points as abbreviations.
Returns: the output stream
template <class CharT, class Traits> std::basic_ostream<CharT, Traits>& duration_long(std::basic_ostream<CharT, Traits>& os);
Effects: Set the duration_punct facet to stream
durations and time_points as long text.
Returns: the output stream
Any duration can be streamed out
to a basic_ostream. The
run-time value of the duration is formatted according
to the rules and current format settings for duration::rep. This is followed by a single space
and then the compile-time unit name of the duration. This unit name is
built on the string returned from ratio_string<> and the data used to construct
the duration_punct which was inserted
into the stream's locale. If a duration_punct has not been
inserted into the stream's locale, a default constructed duration_punct will be added
to the stream's locale.
A time_point is formatted by outputting
its internal duration followed by a string
that describes the time_point::clock epoch. This string will vary
for each distinct clock, and for each implementation of the supplied
clocks.
template <class CharT, class Traits, class Rep, class Period> std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const duration<Rep, Period>& d);
Effects: outputs the duration as an abrevieated or
long text format depending on the state of the duration_punct facet.
Returns: the output stream
template <class CharT, class Traits, class Rep, class Period> std::basic_istream<CharT, Traits>& operator>>(std::basic_istream<CharT, Traits>& is, duration<Rep, Period>& d)
Effects: reads a duration from the input stream.
If a format error is found, the input stream state will be set to failbit.
Returns: the input stream
template <class CharT, class Traits, class Clock, class Duration> std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const time_point<Clock, Duration>& tp);
Effects: outputs the time_point as an abrevieated
or long text format depending on the state of the duration_punct facet.
Returns: the output stream
template <class CharT, class Traits, class Clock, class Duration> std::basic_istream<CharT, Traits>& operator>>(std::basic_istream<CharT, Traits>& is, time_point<Clock, Duration>& tp);
Effects: reads a time_point from the input stream.
If a format error is found, the input stream state will be set to failbit.
Returns: the input stream
namespace boost { namespace chrono { template <class To, class Rep, class Period> To floor(const duration<Rep, Period>& d); } }
This function round down the given parameter.
namespace boost { namespace chrono { template <class To, class Rep, class Period> To round(const duration<Rep, Period>& d); } }
This function round to nearest, to even on tie the given parameter.
namespace boost { namespace chrono { template <class To, class Rep, class Period> To ceil(const duration<Rep, Period>& d); } }
This function round up the given parameter.
BOOST_CHRONO_HAS_PROCESS_CLOCKS
process_real_cpu_clockprocess_user_cpu_clockprocess_system_cpu_clockprocess_cpu_clockprocess_timesprocess_times Input/Outputduration_values Specialization for process_times<>clock_string<process_real_cpu_clock>
Specializationclock_string<process_user_cpu_clock>
Specializationclock_string<process_system_cpu_clock>
Specializationclock_string<process_cpu_clock>
Specializationnumeric_limits Specialization for process_times<>Knowing how long a program takes to execute is useful in both test and production environments. It is also helpful if such timing information is broken down into real (wall clock) time, CPU time spent by the user, and CPU time spent by the operating system servicing user requests.
Process clocks don't include the time spent by the child process.
#define BOOST_CHRONO_HAS_PROCESS_CLOCKS namespace boost { namespace chrono { class process_real_cpu_clock; class process_user_cpu_clock; class process_system_cpu_clock; class process_cpu_clock; template <typename Rep> struct process_times; template <class CharT, class Traits, class Rep> std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, process_times<Rep> const& rhs); template <class CharT, class Traits, class Rep> std::basic_istream<CharT, Traits>& operator>>(std::basic_istream<CharT, Traits>& is, process_times<Rep> const& rhs); template <class Rep> struct duration_values<process_times<Rep> >; template <class CharT> struct clock_string<process_real_cpu_clock, CharT>; struct clock_string<process_user_cpu_clock, CharT>; struct clock_string<process_system_cpu_clock, CharT>; struct clock_string<process_cpu_clock, CharT>; } } namespace std { template <class Rep> class numeric_limits<boost::chrono::process_times<Rep> >; }
This macro is defined if the platform supports process clocks.
process_real_cpu_clock satisfy
the Clock
requirements.
process_real_cpu_clock class
provides access to the real process wall-clock steady clock, i.e. the
real CPU-time clock of the calling process. The process relative current
time can be obtained by calling process_real_cpu_clock::now().
class process_real_cpu_clock { public: typedefnanosecondsduration; typedef duration::rep rep; typedef duration::period period; typedef chrono::time_point<process_real_cpu_clock> time_point; static constexpr bool is_steady = true; static time_point now( ) noexcept; static time_point now( system::error_code & ec ); };
process_user_cpu_clock satisfy
the Clock
requirements.
process_user_cpu_clock class
provides access to the user CPU-time steady clock of the calling process.
The process relative user current time can be obtained by calling process_user_cpu_clock::now().
class process_user_cpu_clock { public: typedefnanosecondsduration; typedef duration::rep rep; typedef duration::period period; typedef chrono::time_point<process_user_cpu_clock> time_point; static constexpr bool is_steady = true; static time_point now( ) noexcept; static time_point now( system::error_code & ec ); };
process_system_cpu_clock satisfy
the Clock
requirements.
process_system_cpu_clock class
provides access to the system CPU-time steady clockof the calling process.
The process relative system current time can be obtained by calling
process_system_cpu_clock::now().
class process_system_cpu_clock { public: typedefnanosecondsduration; typedef duration::rep rep; typedef duration::period period; typedef chrono::time_point<process_system_cpu_clock> time_point; static constexpr bool is_steady = true; static time_point now( ) noexcept; static time_point now( system::error_code & ec ); };
process_cpu_clock can
be considered as a tuple<process_real_cpu_clock, process_user_cpu_clock, process_system_cpu_clock>.
process_cpu_clock provides
a thin wrapper around the operating system's process time API. For POSIX-like
systems, that's the times() function, while for Windows, it's the GetProcessTimes()
function.
The process relative real, user and system current time can be obtained
at once by calling process_clocks::now().
class process_cpu_clock { public: typedef process_times<nanoseconds::rep> times ; typedefduration<times, nano> duration; typedef duration::rep rep; typedef duration::period period; typedef chrono::time_point<process_cpu_clock> time_point; static constexpr bool is_steady = true; static time_point now( ) noexcept; static time_point now( system::error_code & ec ); };
This class is the representation of the process_cpu_clock::duration
class. As such it needs to implements the arithmetic operators.
template <typename Rep> struct process_times : arithmetic<process_times<Rep>, multiplicative<process_times<Rep>, Rep, less_than_comparable<process_times<Rep> > > > { Rep real; // real (i.e wall clock) time Rep user; // user cpu time Rep system; // system cpu time times(); times( process_real_cpu_clock::rep r, process_user_cpu_clock::rep u, process_system_cpu_clock::rep s); template <typename Rep2> explicit process_times( Rep2 r); template <typename Rep2> explicit process_times( process_times<Rep2> const& rhs); operator rep() const; bool operator==(process_times const& rhs); template <typename Rep2> bool operator==(process_times<Rep2> const& rhs); times operator+=(process_times const& rhs); times operator-=(process_times const& rhs); times operator*=(process_times const& rhs); times operator/=(process_times const& rhs); bool operator<(process_times const & rhs) const; };
template <class CharT, class Traits, class Rep> std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, process_times<Rep> const& rhs);
Effects: Output each part separated by ';' and sourrounded by '{', '}'.
Throws: None.
template <class CharT, class Traits, class Rep> std::basic_istream<CharT, Traits>& operator>>(std::basic_istream<CharT, Traits>& is, process_times<Rep> const& rhs);
Effects: overrides the value of rhs if the input stream has the format "{r;u;s}". Otherwise, set the input stream state as failbit | eofbit.
Throws: None.
template <class Rep>
struct duration_values<process_times<Rep> >
{
static process_times<Rep> zero();
static process_times<Rep> max();
static process_times<Rep> min();
};
The times specific functions
zero(),
max()
and min()
uses the relative functions on the representation of each component.
template <class CharT> struct clock_string<process_real_cpu_clock, CharT> { static std::basic_string<CharT> name(); static std::basic_string<CharT> since(); };
clock_string<>::name()
returns "process_real_cpu_clock".
clock_string<>::since()
returns " since process start-up"
template <class CharT> struct clock_string<process_user_cpu_clock, CharT> { static std::basic_string<CharT> name(); static std::basic_string<CharT> since(); };
clock_string<>::name()
returns "process_user_cpu_clock".
clock_string<>::since()
returns " since process start-up"
template <class CharT> struct clock_string<process_system_cpu_clock, CharT> { static std::basic_string<CharT> name(); static std::basic_string<CharT> since(); };
clock_string<>::name()
returns "process_system_cpu_clock".
clock_string<>::since()
returns " since process start-up"
template <class CharT> struct clock_string<process_cpu_clock, CharT> { static std::basic_string<CharT> name(); static std::basic_string<CharT> since(); };
clock_string<>::name()
returns "process_cpu_clock".
clock_string<>::since()
returns " since process start-up"
namespace std { template <> class numeric_limits<boost::chrono::process_times<Rep>> { typedef boost::chrono::process_times<Rep> Res; public: static const bool is_specialized = true; static Res min(); static Res max(); static Res lowest(); static const int digits; static const int digits10; static const bool is_signed = false; static const bool is_integer = true; static const bool is_exact = true; static const int radix = 0; }; }
The process_times<Rep>
specialization functions min(), max() and lowest() uses the relative functions on the
representation of each component.
Notes
min()
returns the tuple of mins.
max()
returns the tuple of maxs.
lowest()
returns the tuple of lowests.
digits is the sum
of (binary) digits.
digits10 is the sum
of digits10s.
Knowing the time a thread takes to execute is useful in both test and production environments.
#define BOOST_CHRONO_HAS_THREAD_CLOCK #define BOOST_CHRONO_THREAD_CLOCK_IS_STEADY namespace boost { namespace chrono { class thread_clock; template <class CharT> struct clock_string<thread_clock, CharT>; } }
This macro is defined if the platform supports thread clocks.
This macro is defined if the platform has a thread clock. Its value is true if it is steady and false otherwise.
thread_clock satisfy the Clock
requirements.
thread_clock class provides
access to the real thread wall-clock, i.e. the real CPU-time clock of
the calling thread. The thread relative current time can be obtained
by calling thread_clock::now().
class thread_clock { public: typedefnanosecondsduration; typedef duration::rep rep; typedef duration::period period; typedef chrono::time_point<thread_clock> time_point; static constexpr bool is_steady = BOOST_CHRONO_THREAD_CLOCK_IS_STEADY; static time_point now( ) noexcept; static time_point now( system::error_code & ec ); };
#if defined(BOOST_CHRONO_HAS_THREAD_CLOCK) template <class CharT> struct clock_string<thread_clock, CharT> { static std::basic_string<CharT> name(); static std::basic_string<CharT> since(); }; #endif
clock_string<>::name()
returns "thread_clock".
clock_string<>::since()
returns " since thread start-up"