Why is my insert into std::map failing?

Question

In my header file, I'm declaring a map like so:

std::map<LPD3DXSPRITE, LPDIRECT3DTEXTURE9> sprites;

In my C++ file, I am trying to insert like so:

sprites.insert(sprite, texture);

The types I am passing to sprites.insert are correct. Why can I not insert this way? What is the proper way to insert? When I do this, the error I get is like this (snipped):

error C2664: 'std::_Tree<_Traits>::iterator std::_Tree<_Traits>::insert(std::_Tree<_Traits>::iterator,const std::pair<_Ty1,_Ty2> &)' : cannot convert parameter 1 from 'LPD3DXSPRITE' to 'std::_Tree<_Traits>::iterator'

"The types I am passing to sprites.insert are correct" ORLY? ;-) — Steve Jessop
– Steve Jessop, Commented Nov 24, 2009 at 0:53
@Steve the types matched the types I'd assigned in my map :) — Chris
– Chris, Commented Nov 24, 2009 at 3:35

Charles Salvia · Accepted Answer · 2009-11-24 00:30:39Z

You need to wrap your key and value in an std::pair object:

sprites.insert(std::make_pair(sprite, texture));

This is because std::map is a Pair Associative Container. The value_type of std::map<K,V> is std::pair<const K,V>.

s1n · Accepted Answer · 2009-11-24 00:17:57Z

3

Alternatively, you could use operator[]. For std::map, this will autovivify for you. Depending on what you are doing, it may make calling std::map::insert unnecessary.

answered Nov 24, 2009 at 0:17

s1n

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1 Comment

stefanB Over a year ago

insert will check if the value already exists in map, operator[] sets the value for key without checking so it depends on what functionality you need

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