Is it correct to use map:insert() or []?

When adding data to the map

I know there are two ways, but I want to know the difference between the two and which one is right (standard?).

2022-09-21 21:26

1 Answers

For map[key] = value;, there is no way to determine if the value corresponding to key is newly created or if the existing value has changed.

map::insert() can distinguish the two, and the usage is as follows

int main ()
{
  std::map<char,int> mymap;

  // // first insert function version (single parameter):
  mymap.insert ( std::pair<char,int>('a',100) );
  mymap.insert ( std::pair<char,int>('z',200) );

  std::pair<std::map<char,int>::iterator,bool> ret;
  ret = mymap.insert ( std::pair<char,int>('z',500) );
  if (ret.second==false) {
    std::cout << "element 'z' already existed";
    std::cout << " with a value of " << ret.first->second << '\n';
  }
}

Code source: std:map::insert

2022-09-21 21:26

If you have any answers or tips

Popular Tags

python x 4647

android x 1593

java x 1494

javascript x 1427

c x 927

c++ x 878

ruby-on-rails x 696

php x 692

python3 x 685

html x 656