std::map default value

Question

Is there a way to specify the default value std::map\'s operator[] returns when an key does not exist?

Answer 1

Expanding on the answer https://stackoverflow.com/a/2333816/272642, this template function uses std::map's key_type and mapped_type typedefs to deduce the type of key and def. This doesn't work with containers without these typedefs.

template 
typename C::mapped_type getWithDefault(const C& m, const typename C::key_type& key, const typename C::mapped_type& def) {
    typename C::const_iterator it = m.find(key);
    if (it == m.end())
        return def;
    return it->second;
}

This allows you to use

std::map m;
int* v = getWithDefault(m, "a", NULL);

without needing to cast the arguments like std::string("a"), (int*) NULL.