muduo_base 源码分析：Timestamp

Epoch:1970-01-01 00:00:00 +000(UTC)

Timestamp类结构代码：muduo/muduo/base/Timestamp.h

class Timestamp : public muduo::copyable,public boost::less_than_comparable<Timestamp>{public:Timestamp() : microSecondsSinceEpoch_(0){}explicit Timestamp(int64_t microSecondsSinceEpochArg): microSecondsSinceEpoch_(microSecondsSinceEpochArg){}void swap(Timestamp& that)           //交换两个时间{std::swap(microSecondsSinceEpoch_, that.microSecondsSinceEpoch_);}string toString() const              //返回时间的秒数微秒数{//… …snprintf(buf, sizeof(buf)-1, "%" PRId64 ".%06" PRId64 "", seconds, microseconds);}string toFormattedString(bool showMicroseconds = true) const  //将时间格式化输出{//… …snprintf(buf, sizeof(buf), "%4d%02d%02d %02d:%02d:%02d.%06d",tm_time.tm_year + 1900, tm_time.tm_mon + 1, tm_time.tm_mday,tm_time.tm_hour, tm_time.tm_min, tm_time.tm_sec,microseconds);snprintf(buf, sizeof(buf), "%4d%02d%02d %02d:%02d:%02d",tm_time.tm_year + 1900, tm_time.tm_mon + 1, tm_time.tm_mday,tm_time.tm_hour, tm_time.tm_min, tm_time.tm_sec);//… …}bool valid() const { return microSecondsSinceEpoch_ > 0; }int64_t microSecondsSinceEpoch() const { return microSecondsSinceEpoch_; } //返回从Epoch到现在的微秒数time_t secondsSinceEpoch() const//返回从Epoch到现在的秒数{return static_cast<time_t>(microSecondsSinceEpoch_ / kMicroSecondsPerSecond);}static Timestamp now();                 //获取现在时间static Timestamp invalid(){return Timestamp();}static Timestamp fromUnixTime(time_t t){return fromUnixTime(t, 0);}static Timestamp fromUnixTime(time_t t, int microseconds){return Timestamp(static_cast<int64_t>(t)* kMicroSecondsPerSecond + microseconds);}static const int kMicroSecondsPerSecond = 1000 * 1000;    //1s=1000000usprivate:int64_t microSecondsSinceEpoch_;               //微秒};//计算时间差，返回秒数  inline double timeDifference(Timestamp high, Timestamp low){int64_t diff = high.microSecondsSinceEpoch() - low.microSecondsSinceEpoch();return static_cast<double>(diff) / Timestamp::kMicroSecondsPerSecond;}//时间相加inline Timestamp addTime(Timestamp timestamp, double seconds){int64_t delta = static_cast<int64_t>(seconds * Timestamp::kMicroSecondsPerSecond);return Timestamp(timestamp.microSecondsSinceEpoch() + delta);}

Timestamp 继承copyable，对象可拷贝
C++对象的两种语义
1． 值语义：可以拷贝，拷贝之后与原对象脱离关系
2． 对象语义:一种是不能拷贝，一种是可以拷贝，拷贝之后与原对象仍然存在一定关系，比如共享底层资源(要实现自己的拷贝构造函数)

Timestamp 继承 less_than_comparable,只需要实现运算符’<’,可自动实现”>, >=, <=”
BOOST_STATIC_ASSERT 可在编译期间断言,
assert 是运行时的断言
int64_t用来表示64位整数，在32位系统中是long long int，在64位系统中是long int,所以打印int64_t的格式化方法是：
printf(“%ld”, value); // 64bit OS
printf("%lld", value); // 32bit OS
跨平台的做法：
#define __STDC_FORMAT_MACROS
#include <inttypes.h>
#undef __STDC_FORMAT_MACROS
printf("%" PRId64 "\n", value);