Tech Sujhav : How to create insert and read map in map using std::map

Let check how we can code for following image where there are 3 Maps placed inside one another. As we know Map as two elements 1.Key and 2.Data (mapped to key) here data is nothing but an another map.

typedef std::map<string,vector<string>> InnerMostMap;
typedef std::map<string,vector<string>>::iterator InnerMostMapItr;

typedef std::map<string,InnerMostMap> MidMap;

typedef std::map<string,InnerMostMap>:: iterator MidMapItr;

std::map<string,std::map<string,vector<string>>> MidMap;

typedef std::map<string,MidMap> OutMap;
typedef std::map<string,MidMap>::iterator OutMapItr;

std::map<string,std::map<string,std::map<string,vector<string>>>> OutMap

Nested Map, [Map inside Map]

Strategy to follow:

If KEY is to be added for the first time in map then one can use directly use map::insert()
If KEY is already exist and then you want to add/modify the data against that key then

use map::find() to know at which place KEY exist in map
then modify/update the data.

It is very simple to use auto datatype rather iterator.
Best practice is to use try and catch.

Let check following code to understand, COPY, PASTE on any online compiler & RUN

NOTE:- First check output of below code then come back to code again and focus of comments.

#include<iostream>

#include<map>
#include<vector>
using namespace std;

typedef std::map<string,vector<string>> InnerMostMap;
typedef std::map<string,vector<string>>::iterator InnerMostMapItr;

typedef std::map<string,InnerMostMap> MidMap;
typedef std::map<string,InnerMostMap>:: iterator MidMapItr;

typedef std::map<string,MidMap> OutMap;
typedef std::map<string,MidMap>::iterator OutMapItr;

//g_completeMap is a actual map Object
//that we are going to fill and read
OutMap g_completeMap;

//Function to iterate complete map
//and display values. i.e. read values from map
void display_map()
{
   for(auto l_outMapRowObj:g_completeMap )
   {
       cout<<"OutMap Key:: "<<l_outMapRowObj.first<<endl;
       for(auto l_midMapRowObj:l_outMapRowObj.second )
       {
           cout<<"\t MidMap Key::"<<l_midMapRowObj.first<<endl;
           for(auto l_innrMapRowObj:l_midMapRowObj.second )
           {
               cout<<"\t\t InnerMap Key::"<<l_innrMapRowObj.first<<endl;
               for(auto l_vectorElement : l_innrMapRowObj.second )
               {
                   cout<<"\t\t\t Vector Value::"<<l_vectorElement<<endl;
               }
           }
       }
   }
}
int main()
{
   try
   {
       //First Entry in Inner Most map
       std::vector<string> l_vector ;
       l_vector.push_back("First_Entry_Vector");
       InnerMostMap l_innerMap;
       l_innerMap.insert(std::pair<string,vector<string>>("first_key_inner",l_vector));

       //First Entry in MidMap
       MidMap l_midMap;
       l_midMap.insert(std::pair<string,InnerMostMap>("first_key_mid",l_innerMap));

     //First entry in Actual OutMap
       g_completeMap.insert(std::pair<string,MidMap>("first_key_outer",l_midMap));

       //display Value- Check what is inserted in map.
       display_map();
        //Check Output Now
       //**********************************************************//
       //Enter following New-Value in map on Existing KEY
       //first_key_outer::first_key_mid::first_key_inner::[Second_Entry_Vector]
       // Means only entry to be added in already existing Vector
       //**********************************************************//

       OutMapItr l_outMapItr;
       l_outMapItr=g_completeMap.find("first_key_outer");
       if(l_outMapItr == g_completeMap.end())
       {
           cout<<"first_key_outer not foud in MAP" <<endl;
           //Write code here if we want to add new entry in
           //outmap with new Key
       }
       else
       {
           //now we have reached to first_key_outer
           //now go to second of first_key_outer
          //i.e. (Value of first_key_outer)
           //then in value reach to first_key_mid

           //Create Mid key iterator
           MidMapItr l_midKeyItr;

           //with l_outMapItr->second reaches to MidMap
           //with .find() looks for first_key_mid in MidMap
           l_midKeyItr=(l_outMapItr->second).find("first_key_mid");

         if(l_midKeyItr == (l_outMapItr->second).end())
           {
             //Key first_key_mid is not found
           }
           else
           {
             //first_key_mid is found
               //now go to second of first_key_mid
              //i.e. (Value of first_key_mid)
               //then in that Value (second)find for first_key_inner

               //Create Inner Map iterator
               InnerMostMapItr l_innerMapItr;

               //with l_midKeyItr->second reaches to MidMap
               //with .find() looks for first_key_inner in MidMap
               l_innerMapItr=(l_midKeyItr->second).find("first_key_inner");

               if(l_innerMapItr == (l_midKeyItr->second).end())
               {
                   //first_key_inner not found
               }
               else
               {
                   //now go to first_key_inner value i.e Vector
                   //l_innerMapItr->second i.e. reaches to Vector
                   //Now push_back to put "Second_Entry_Vector"

                   (l_innerMapItr->second).push_back("Second_Entry_Vector");
               }
           }
       }
       cout<<"*** Second_Entry_Vector - inserted ***"<<endl;
       display_map();
      //Check Output Now
       //****************************************************//
      //Enter following Value in map
       // first_key_outer::first_key_mid::second_key_inner::[first_Entry_Vector]
       // Means only entry to be added in already existing Vector
       //*****************************************************//
       l_outMapItr=g_completeMap.find("first_key_outer");
       if(l_outMapItr == g_completeMap.end())
       {
           cout<<"first_key_outer not foud in MAP" <<endl;
           //Write code here if we want to add new entry in
           //outmap with new Key
       }
       else
       {
           //now we have reached to first_key_outer
           //now go to second of first_key_outer
          //i.e.(Value of first_key_outer)
           //then in value/data reach to first_key_mid

           //Create Mid key iterator
           MidMapItr l_midKeyItr;

           //with l_outMapItr->second reaches to MidMap
           //with .find() looks for first_key_mid in MidMap
           l_midKeyItr=(l_outMapItr->second).find("first_key_mid");
         if(l_midKeyItr == (l_outMapItr->second).end())
           {
               //Key first_key_mid is not found
           }
           else
           {
               //first_key_mid is found
               //now go to second of first_key_mid
              //i.e. (Value of first_key_mid)
               //then in that Value/Data (second)find for first_key_inner
             //Create Inner Map iterator
               InnerMostMapItr l_innerMapItr;

               //with l_midKeyItr->second reaches to MidMap
               //with .find() looks for first_key_inner in MidMap
                l_innerMapItr=(l_midKeyItr->second).find("second_key_inner");

               if(l_innerMapItr == (l_midKeyItr->second).end())
               {
                   //************************************/
                   //second_key_inner not found
                   //Create Vector to put at second_key_inner
                                               //*************************************/
                   std::vector<string> l_vector ;
                 l_vector.push_back("First_Entry_Vector");
                   (l_midKeyItr->second).insert(std::pair<string,vector<string>>("second_key_inner",l_vector));;
              }
               else
               {
                   //now go to first_key_inner value i.e Vector
                   //l_innerMapItr->second i.e. reaches to Vector
                   //Now push_back to put "Second_Entry_Vector"

                   (l_innerMapItr->second).push_back("Second_Entry_Vector");
               }
           }
       }
               cout<<"*** second_key_inner - inserted ***"<<endl;
    //Check Output Now
     display_map();
   }
   catch(...)
   {
       cout<<"Exception "<<endl;
   }
}

COMPILE:

g++ map.cpp –o map

OUTPUT:

OutMap Key:: first_key_outer

MidMap Key::first_key_mid

InnerMap Key::first_key_inner

Vector Value::First_Entry_Vector

*** Second_Entry_Vector - inserted ***

OutMap Key:: first_key_outer

MidMap Key::first_key_mid

InnerMap Key::first_key_inner

Vector Value::First_Entry_Vector

Vector Value::Second_Entry_Vector

*** second_key_inner - inserted ***

OutMap Key:: first_key_outer

MidMap Key::first_key_mid

InnerMap Key::first_key_inner

Vector Value::First_Entry_Vector

Vector Value::Second_Entry_Vector

InnerMap Key::second_key_inner

Vector Value::First_Entry_Vector

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Tech Sujhav

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How to create insert and read map in map using std::map

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