Question

Here is some working code:

std::pair<typename std::map< time_t, T >::iterator, bool> ret;    
ret = prt_map->insert ( std::pair< time_t, T >( seconds , value ) );
if (ret.second == false) // exists
{
 ... update exising value
}

I want to upgrade it to max efficient inserting code and give a tip to insert that need to start from –prt_map->end(); something like:

  prt_map->insert ( --prt_map->end(), std::pair< time_t, T >( seconds , value ) );

but this insert function prototupe does not return std::pair with bool that notify that value added or not ( to check for existing and update if so… How to solve this to have ability to update existing value?

Answer 1

The post condition of a.insert(hint, t) is:

a contains an element whose key is the same as that of t. The size of a is incremented by either 1 or 0.

which should be sufficient information to determine whether or not the element was inserted.