时间和日期
Boost使用的timer和data_timerj进行对应和时间日期相关的出来文档，timer包含三个组件，分别为timer，progress_timer以及对应的progress_display.
timer
timer可以测量运行时间
timer类摘要
lass timer
{
public:
timer() { _start_time = std::clock(); } // postcondition: elapsed()==0
// timer( const timer& src ); // post: elapsed()==src.elapsed()
// ~timer(){}
// timer& operator=( const timer& src ); // post: elapsed()==src.elapsed()
void restart() { _start_time = std::clock(); } // post: elapsed()==0
double elapsed() const // return elapsed time in seconds
{ return double(std::clock() - _start_time) / CLOCKS_PER_SEC; }
double elapsed_max() const // return estimated maximum value for elapsed()
// Portability warning: elapsed_max() may return too high a value on systems
// where std::clock_t overflows or resets at surprising values.
{
return (double((std::numeric_limits::max)())
- double(_start_time)) / double(CLOCKS_PER_SEC);
}
double elapsed_min() const // return minimum value for elapsed()
{ return double(1)/double(CLOCKS_PER_SEC); }
private:
std::clock_t _start_time;
}; // timer
} // namespace boost demo1
#include
#include
using namespace boost;
int main(int argc, char const *argv[])
{
timer t;
std::cout << "max timespan:" << t.elapsed_max() << std::endl;
std::cout << "min timespan:" << t.elapsed_min() << std::endl;
std::cout <<"now time elapsed:" << t.elapsed()<< "s" < 输出的结果
$ ./a.out
max timespan:9.22337e+12
min timespan:1e-06
now time elapsed:0.000256sprogress_timer
progress_timer测量经过的时间（使用计时器），销毁时显示。其继承于timer
progress_timer类摘要
class progress_timer : public timer, private noncopyable
{
public:
explicit progress_timer( std::ostream & os = std::cout )
// os is hint; implementation may ignore, particularly in embedded systems
: timer(), noncopyable(), m_os(os) {}
~progress_timer()
{
// A) Throwing an exception from a destructor is a Bad Thing.
// B) The progress_timer destructor does output which may throw.
// C) A progress_timer is usually not critical to the application.
// Therefore, wrap the I/O in a try block, catch and ignore all exceptions.
try
{
// use istream instead of ios_base to workaround GNU problem (Greg Chicares)
std::istream::fmtflags old_flags = m_os.setf( std::istream::fixed,
std::istream::floatfield );
std::streamsize old_prec = m_os.precision( 2 );
m_os << elapsed() << " s\n" // "s" is System International d'Unites std
<< std::endl;
m_os.flags( old_flags );
m_os.precision( old_prec );
}
catch (...) {} // eat any exceptions
} // ~progress_timer
private:
std::ostream & m_os;
};demo2例子
#include
#include
using namespace std;
using namespace boost;
void cost_timer(){
boost::progress_timer t;
int i = 0;
while (i < 10000000)
{
i++;
}
return;
}
int main(int argc, char const *argv[])
{
cost_timer();
return 0;
}
输出结果
./boost_timer_demo2
0.05 sprogress_display
显示已知目标的进度指示。
progress_display类摘要
class progress_display : private noncopyable
{
public:
explicit progress_display( unsigned long expected_count_,
std::ostream & os = std::cout,
const std::string & s1 = "\n", //leading strings
const std::string & s2 = "",
const std::string & s3 = "" )
// os is hint; implementation may ignore, particularly in embedded systems
: noncopyable(), m_os(os), m_s1(s1), m_s2(s2), m_s3(s3) { restart(expected_count_); }
void restart( unsigned long expected_count_ )
// Effects: display appropriate scale
// Postconditions: count()==0, expected_count()==expected_count_
{
_count = _next_tic_count = _tic = 0;
_expected_count = expected_count_;
m_os << m_s1 << "0% 10 20 30 40 50 60 70 80 90 100%\n"
<< m_s2 << "|----|----|----|----|----|----|----|----|----|----|"
<< std::endl // endl implies flush, which ensures display
<< m_s3;
if ( !_expected_count ) _expected_count = 1; // prevent divide by zero
} // restart
unsigned long operator+=( unsigned long increment )
// Effects: Display appropriate progress tic if needed.
// Postconditions: count()== original count() + increment
// Returns: count().
{
if ( (_count += increment) >= _next_tic_count ) { display_tic(); }
return _count;
}
unsigned long operator++() { return operator+=( 1 ); }
unsigned long count() const { return _count; }
unsigned long expected_count() const { return _expected_count; }
private:
std::ostream & m_os; // may not be present in all imps
const std::string m_s1; // string is more general, safer than
const std::string m_s2; // const char *, and efficiency or size are
const std::string m_s3; // not issues
unsigned long _count, _expected_count, _next_tic_count;
unsigned int _tic;
void display_tic()
{
// use of floating point ensures that both large and small counts
// work correctly. static_cast<>() is also used several places
// to suppress spurious compiler warnings.
unsigned int tics_needed = static_cast((static_cast(_count)
/ static_cast(_expected_count)) * 50.0);
do { m_os << '*' << std::flush; } while ( ++_tic < tics_needed );
_next_tic_count =
static_cast((_tic/50.0) * static_cast(_expected_count));
if ( _count == _expected_count ) {
if ( _tic < 51 ) m_os << '*';
m_os << std::endl;
}
} // display_tic
}; demo使用例子
#include
#include
#include
#include
#include
using namespace std;
using namespace boost;
int main(int argc, char const *argv[])
{
vector v(100);
for(int i = 0; i < 100 ; i++){
v[i] = i;
}
ofstream fs("demo.txt");
progress_display pd(v.size());
vector::iterator pos;
for (pos = v.begin(); pos < v.end(); pos++)
{
fs << *pos;
++pd;
}
return 0;
} 输出的结果为：
$ ./boost_timer_demo3
0% 10 20 30 40 50 60 70 80 90 100%
|----|----|----|----|----|----|----|----|----|----|
***************************************************