Re: std::map lookup function
Thorsten Ottosen wrote:
James Kanze wrote:
Matthias Kluwe wrote:
In my current (toy) project I need to lookup values in a
std::map. As this is constructed from user input, given keys
can't be trusted, and I find myself doing things like
std::map<...,...>::iterator it = map.find( key );
if ( it != map.end() ) {
...
}
very often.
Don't we all.
I'd like to implement a function which does the lookup,
returns a reference to the mapped object and throws an
exception if the given key is not present.
I generally return a pointer to the mapped object -- null if
it isn't present.
FWIW, The C++0x working paper already contains:
reference at( const Key& );
const_reference at( const Key& ) const;
That doesn't sound like a good idea to me. Depending on the
actual use, not finding the key is either a programming error
(rare, but it does occur), or an expected condition. In the
first case, the code should abort, and in the second, the
condition should be part of the return value -- I don't want to
have to start using exceptions as part of my main programming
logic.
C++ has a defined sentinal value for pointers. This sounds like
the perfect case to use it. Something like:
pointer get( Key const& ) ;
const_pointer get( Key const& ) const ;
--
James Kanze GABI Software
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