Function to provide a default value when working with std::map

I am trying to write a function, which will give me a default value when the key is not inside a std::map. In all cases will my default value be numerical_limit::infinity().
Hovewer this simple example is not working.

#include <iostream>
#include <map>
#include <limits>

template<typename KeyType, typename ValueType>
ValueType mapDefaultInf(const std::map<KeyType, ValueType> & map, const KeyType & key)
{
    if(!map.contains(key))
    {
        return std::numeric_limits<ValueType>::infinity();
    }
    else
    {
        return map[key];
    }
}

int main()
{
    std::map<std::string, int> map;
    auto el = mapDefaultInf(map, "alexey");
    std::cout << el << std::endl;

    return 0;
}

Error is:

main.cpp:29:42: error: no matching function for call to ‘mapDefaultInf(std::map, int>&, const char [7])’

Can someone help me understand the error.

Thanks in advance.

>Solution :

First of all you use operator[] on the map object inside the function. That will never be allowed because it is a non-const function and you have passed the map by const reference. Instead you should rewrite the function implementation to use iterators:

template<typename KeyType, typename ValueType>
ValueType mapDefaultInf(const std::map<KeyType, ValueType> & map, const KeyType & key)
{
    const auto it = map.find(key);
    return it != map.end() ?  it->second : std::numeric_limits<ValueType>::infinity();
}

Second of all you have an ambiguity in the key type. You need to pass in a std::string. Like this:

auto el = mapDefaultInf(map, std::string("alexey"));