Question

Foo.h :

class Foo
{
public:
    Foo(void);
    ~Foo(void);   

    void AddScreen(std::string name, ScreenBase &screenToAdd);

private:

    std::map<std::string, ScreenBase> m_screens;
};

Foo.cpp :

void Foo::AddScreen(string name, ScreenBase &screenToAdd)
{
    m_screens[name] = screenToAdd; 
}

the last line creates a compile error C2784: ‘bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)’ : could not deduce template argument for ‘const std::

commenting out the last line and the compile succeeds.

I’m new to c++ (coming from a managed language) and don’t know why I can’t populate the map with this.

Any insight is appreciated. Thanks.

ScreenBase.h :

    #pragma once
    class ScreenBase
    {
    public:
        ScreenBase();
        ~ScreenBase();

        virtual void Update(float tt, float dt);
        virtual void Render();
    };

ScreenBase.cpp :

#include "pch.h"
#include "ScreenBase.h"

ScreenBase::ScreenBase(void)
{
}
ScreenBase::~ScreenBase(void)
{
}
void ScreenBase::Update(float tt, float dt)
{

}
void ScreenBase::Render()
{

}

Answer 1

You forgot to add the following line to Foo.cpp

#include <string>

That should fix it.

The reason that fixes it is because the “<” operator between 2 std::string objects is defined there. Since std::map is an associative array, it will sort the keys with either a specific sorting function you specify (as a third parameter for the template, e.g. std::map<int, MyObj, MyIntCompareFunctor>), or it will default to using < operator of the key type which in your case is std::string.

P.S. Also, pass strings by reference, not value:
e.g. void foo(const std::string& bar){};