mongodb插入datetime类型所用函数appendDate的参数Date_t详解

源码：

struct MONGO_CLIENT_API Date_t {
// TODO: make signed (and look for related TODO's)
unsigned long long millis;
Date_t() : millis(0) {}
Date_t(unsigned long long m) : millis(m) {}
operator unsigned long long&() {
return millis;
}
operator const unsigned long long&() c {
return millis;
}
void toTm(tm* buf);
std::string toString() const;
time_t toTimeT() const;
int64_t asInt64() const {
return static_cast<int64_t>(millis);
}
bool isFormatable() const;
};

需要注意的是Date_t(unsigned long long m)的输入一定是毫秒级别的时间戳，否则得到的Date_t有错误