Question

Is there any method to find the amount/size of memory allocated to a map in c++?
There is a function to find the size of the map,ie,number of entries in the map, but is there any such method for the memory.
I have a map ( string, string).
The sizeof() is always giving me a size of 48. Any reason why this is so?
Thanks 🙂

Answer 1

No, there is not. However you can achieve something similar for classes that support a .size method such as strings or standard container:

template <class Key, class Value>
unsigned long mapSize(const std::map<Key,Value> &map){
    unsigned long size = sizeof(map);
    for(typename std::map<Key,Value>::const_iterator it = map.begin(); it != map.end(); ++it){
        size += it->first.size();
        size += it->second.size();
    }
    return size;
}

If you want to know the allocated memory you could use .capacity:

template <class Key, class Value>
unsigned long mapCapacity(const std::map<Key,Value> &map){
    unsigned long cap = sizeof(map);
    for(typename std::map<Key,Value>::const_iterator it = map.begin(); it != map.end(); ++it){
        cap += it->first.capacity();
        cap += it->second.capacity();
    }
    return cap;
}