Modern Cpp记录

#include <iostream>
# include <set>
#include <chrono>
#ifndef   UNUSED
#define   UNUSED(v)   (void)(v)
#endif
typedef std::chrono::time_point<std::chrono::system_clock, std::chrono::nanoseconds> time_point;
//void logg(const time_point& tp, std::string& name)
void logg(const time_point& tp, const std::string& name)
{
    UNUSED(tp);
    UNUSED(name);
    std::cout << " name: " << name << std::endl;
}
void log_add(const std::string& name, std::multiset<std::string>& names)
{
    auto now = std::chrono::system_clock::now();
    std::string temp("abc");
    logg(now, std::string("xxx"));
    logg(now, "xxx");
    logg(now, temp);
    names.emplace(name);
}
template <typename T>
void log_add_T(T&& name, std::multiset<std::string>& names)
{
    auto now = std::chrono::system_clock::now();
    logg(now, "xxx");
    names.emplace(std::forward<T>(name));
}
int main(int argc, char *argv[])
{
    std::multiset<std::string> nameset;
    log_add("abcd", nameset);
    log_add_T("aaa", nameset);
    return 0;
}

　　

1. 如果采用logg函数的形式为 void logg(const time_point& tp, std::string& name)， 则

    logg(now, std::string("xxx"));

    logg(now, "xxx");

  都会编译失败。

2. log_add_T函数采用万能引用参数，利用完美转发，效率比log_add高！