Re: stl::map: return default value without inserting a new element?

From:

Keith H Duggar <duggar@alum.mit.edu>

Newsgroups:

comp.lang.c++

Date:

Tue, 6 Apr 2010 11:18:20 -0700 (PDT)

Message-ID:

<601b47ca-0120-492b-ae63-b93967460491@x7g2000vbc.googlegroups.com>

On Apr 6, 6:46 am, Rui Maciel <rui.mac...@gmail.com> wrote:

In order to avoid wasting resources populating a map with
useless key:value pairs, is there a clean, unencumbered way
to get the value associated with a given key without being
forced to insert new elements or even resort to multiple
lines of code? The closest thing I saw was the map::find()
method, but I believe that ends up forcing to write code to
compare the given iterator to map::end() and, if it matches,
return a default value.

Is there a simpler way to do this?

I find these two functions (including their general semantics)
and variants of them exceedingly useful

template < class K, class V, class C, class A>
V
getOrZero (
   std::map<K,V,C,A> const & m
, K const & k
) {
   typename std::map<K,V,C,A>::const_iterator i = m.find(k) ;
   return i != m.end() ? i->second : V() ;
}

template < class K, class V, class C, class A>
V &
getOrMake (
   std::map<K,V,C,A> & m
, K const & k
) {
   return m[k] ;
}

for all types of containers including STL and custom ones.

KHD