Question

I have a set stores the keys which I want to delete in a map.
I tried the code blow, but it didn’t compile.

std::set<std::string> keys;
std::map<std::string, std::string> mymap;
....
for_each(keys.begin(), keys.end(), boost::bind(&std::map<std::string,   
                                               std::string>::erase, 
                                               &mymap, _1));

Answer 1

You cannot take the address of a Standard Library member function because the declarations of such member functions are unspecified (an implementation is permitted to add additional, optional parameters or add additional overloads to otherwise non-overloaded member functions, so long as the behavior is the same).

The easiest way to do what you are trying to do is:

for (std::set<std::string>::iterator it(keys.begin()); it != keys.end(); ++it)
{
    mymap.erase(*it);
}

If you have a compiler that supports lambda expressions, you might also consider:

std::for_each(keys.begin(), keys.end(), [&mymap](const std::string& key)
{
    mymap.erase(key);
});

If for some reason you really want to use bind, you’ll need to write a function object to call erase:

struct assoc_erase
{
    typedef void result_type;

    template <typename TContainer, typename TKey>
    void operator()(TContainer* container, const TKey& key)
    {
        container->erase(key);
    }
};

// Used as:
std::for_each(keys.begin(), keys.end(), std::bind(assoc_erase(), &mymap, _1));