c++ - Emplace_back instead of push_back on stl containers? -

i'm not quite sure if can replace push_back emplace_back.

i know emplace_back can forward parameters construct object directly in vector without copying twice (perfect forwarding etc...)

and if soemthing this:

vector<a> o; o.emplace_back(a{}); 

then should call copy constructor of a. correct ? same push_back. doesn't ?

are there exceptions? there reasons use push_back ? because easier use emplace_back without thinking it.

the main purpose of emplace perform explicit conversions:

#include <chrono> #include <vector>  using namespace std::chrono_literals;  std::vector<std::chrono::seconds> time;  time.push_back(1s);     // ok // time.push_back(1);   // error, thank god time.emplace_back(1);   // ok, assume know you're doing 

use push_back add element of given value container. use emplace_back explicitly construct element constructor arguments.