error C2995:function template has already been defined

Question

there are many solutions to this question bot nothing answers my case.

I am using VS 2008.I am tring to create a map using Binary search tree

#ifndef _map_h
#define _map_h


#include<string>
using namespace std;

template <typename ValType>
class Map
{
    public:
        Map();
        ~Map();
        ValType getvalue(string key);
        void add(string key,ValType value);

    private:
        struct node{
            string key;
            ValType value;
            node *right;
            node *left;
        };
        node *root;

        node *treeSearch(string key,node *t);

        void treeEnter(string key,ValType value,node *&t);
};
#include"map.cpp"

#endif

map.cpp

#include<string>
#include<iostream>
#include"map.h"
using namespace std;

template <typename ValType>
Map<ValType>::Map(){
    root=NULL;
}

template <typename ValType>
Map<ValType>::~Map(){
    delete root;
}


template <typename ValType>
ValType Map<ValType>::getvalue(string key){
    node *found=treeSearch(key,root);
    if(found==NULL)
        cout<<"Couldnot Found the node";
    else return found->value;
}

template <typename ValType>
typename Map<ValType>::node *Map<ValType>::treeSearch(string key,node *t){
    if(t==NULL) return NULL;

    if(t->key==key) return t;

    if(t->key>key) treeSearch(key,t->left);

    else treeSearch(key,t->right);
}

template <typename ValType>
void Map<ValType>::add(string key,ValType value){
    treeEnter(key,value,root);
}

template <typename ValType>
void Map<ValType>::treeEnter(string key,ValType value,node *&t){
    if(t==NULL){
        t->value=value;
        t->key=key;
        t->left=NULL;
        t->right=NULL;
    }

    else if(t->key==key) t->value=value;

    else if(t->key>key) treeEnter(key,value,t->left);

    else treeEnter(key,value,t->right);
}

Error:For all the functions its saying that they are already been defined.

I am following Stanford online course and the same worked for the instructor(she was using mac)

Answer 1

You have included map.h into map.cpp and map.cpp into map.h. The include guards in map.h will prevent multiple inclusion of map.h and will prevent infinite recursive inclusion. However, if you feed map.cpp to the compiler directly (which is what you are apparently trying to do) it will include map.h once and then map.h will include map.cpp itself one more time. This is what is causing the error.

If you want to implement your template as .cpp file included into .h file, you can do that. This is weird, but it can be forced to work. First and foremost, if you decided to #include your map.cpp, then don't even attempt to compile your map.cpp. Don't feed your map.cpp directly to the compiler. Also, remove #include "map.h" from that .cpp file. There's absolutely no point in doing that.

Your program will have other implementation files, like, say, myprogram.cpp, which will use your map. That myprogram.cpp should include map.h. That myprogram.cpp is what you will feed to the compiler. That way it will work as intended. But trying to compile map.cpp directly will only result in errors.

A better idea though would be not to put anything into a .cpp file. Either put everything into .h file or, if you really want to have it split that way, rename your .cpp file into something else to make it clear to everyone that this is not a translation unit.

Answer 2

In my case, I missed include guards or #pragma once at the top of the header where I defined a template function.