（一）timer库的简介
timer是一个很小的库，提供简单的时间度量和进度显示功能，也可用于性能测试等计时任务。timer库包含三个组件：计时器类timer、progress_timer和进度指示类progress_display。
（二）timer类
timer类可以测量时间的流逝，是一个小型的计时器，提供毫秒级别的计时精度和操作函数。它位于boost命名空间下。使用时需要包含头文件：
include <boost/timer.hpp>
（1）timer的使用
#include <boost/timer.hpp>
#include <iostream>
int main(int argc,char * argv[]){
boost::timer t;
//获取timer能够表示的最大时间精度
std::cout<<"max timespan : "<<t.elapsed_max()/3600<<"h"<<std::endl;
//获取timer能够表示的最小时间精度
std::cout<<"min timespan : "<<t.elapsed_min()<<"s"<<std::endl;
std::cout<<"now time elapsed : "<<t.elapsed()<<"s"<<std::endl;
return 0;
}
timer对象一旦被声明，它的构造函数就启动了计时工作，之后可以调用elapsed()函数获得从对象创建到elapsed()函数调用这段时间间隔。
（2）timer的源码
// boost timer.hpp header file ---------------------------------------------//
// Copyright Beman Dawes 1994-99. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at )
// See for documentation.
// Revision History
// 01 Apr 01 Modified to use new <boost/limits.hpp> header. (JMaddock)
// 12 Jan 01 Change to inline implementation to allow use without library
// builds. See docs for more rationale. (Beman Dawes)
// 25 Sep 99 elapsed_max() and elapsed_min() added (John Maddock)
// 16 Jul 99 Second beta
// 6 Jul 99 Initial boost version
#ifndef BOOST_TIMER_HPP
#define BOOST_TIMER_HPP
#include <boost/config.hpp>
#include <ctime>
#include <boost/limits.hpp>
# ifdef BOOST_NO_STDC_NAMESPACE
namespace std { using ::clock_t; using ::clock; }
# endif
namespace boost {
// timer -------------------------------------------------------------------//
// A timer object measures elapsed time.
// It is recommended that implementations measure wall clock rather than CPU
// time since the intended use is performance measurement on systems where
// total elapsed time is more important than just process or CPU time.
// Warnings: The maximum measurable elapsed time may well be only 596.5+ hours
// due to implementation limitations. The accuracy of timings depends on the
// accuracy of timing information provided by the underlying platform, and
// this varies a great deal from platform to platform.
class 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<std::clock_t>::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
#endif // BOOST_TIMER_HPP
注意：timer中使用了CLOCKS_PER_SEC宏，这个宏在win32下值是1000，而在linux下值是1000000，也就是说它具体平台或编译器相关，所以不适合跨平台使用，也不适合做大跨度时间的测量。
（二）progress_timer类
progress_timer继承自timer，它在析构时自动输出时间。位于boost命名空间下，使用时包含头文件：#include <boost/progress.hpp>。其它用法和timer类似。
如果要在程序中测量一段代码运行时间，可以将这段代码用{}包含起来，同时在{}中一行代码为定义一个progress_timer的对象。
{
boost::progress_timer t; //析构时自动输出时间间隔（从对象创建到析构）
//do something...
}