I created a class MyString and overloaded operator==.
MyString can be used without any problems

class MyString
{
public:
    bool operator== (const MyString& obj) const;
};

I want to use MyString as key in std::map.

std::map<MyString, value> m_xxx;

I can access the inserted data by iterating.

for (auto& it : m_ini)
{
    MyString first = it.first;
    for (auto& sit : it.second)
    {
        MyString key = sit.first;
        MyString value = sit.second; 
        int i = 0;
    }
}

But when using std::map::find the data I inserted cannot be searched

auto& it = m_ini.find(section);
if (it == m_ini.end())

I take for granted that std::map::find will do the comparison through my operator==.But in VS debugger std::map::find single step doesn't break down at my operator== .
I don't know where the problem is, can anyone help me!

CodePudding user response：

std::map does not use operator==. It is a sorted container and by default operator< is used to compare keys of elements in the map.

std::map has 4 template arguments:

template<
    class Key,
    class T,
    class Compare = std::less<Key>,
    class Allocator = std::allocator<std::pair<const Key, T> >
> class map

The third one can be used to select a different comparator. std::less<Key> uses the keys operator<.

Actually a std::map does not care about equality. Two keys a and b are considered equivalent when !(a<b) && !(b<a). Keys are not required to have an operator==.