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Default values in a Map in C++ STL
  • Difficulty Level : Hard
  • Last Updated : 15 Apr, 2020

Prerequisite: Map in STL

A map is a container which is used to store a key-value pair. By default, In Primitive datatypes such as int, char, bool, float in C/C++ are undefined if variables are not initialized, But in a Map, every key is mapped with default value zero when the map is declared. To initialize the map with a random default value below is the approach:

Approach:

  1. Declare a structure(say struct node) with a default value.
  2. Intialise Map with key mapped to struct node.

Syntax:

// For Structure 
struct Node {
   int value = -1;
}

// For Map with every key mapped to default value -1
Map < int, Node > M; 

Below is the illustration of the Map with a default value -1:

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// C++ program to illustrate a Map
// initialise with default value
#include <bits/stdc++.h>
using namespace std;
  
// Structure Node
struct Node {
    int value = -1;
};
  
// Driver Code
int main()
{
    // Map initialise with key value
    // pair with each pair mapped with
    // structure Node
    map<int, Node> Map;
  
    // Print the default value of 1
    // store in Map
    cout << Map[1].value << endl;
  
    return 0;
}

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Output:

-1

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