C++ map update – Simple program example to update value in map. To update an existing value in the map, first we will find the value with the given key using map::find() function. If the key exists, then will update it with new value.
C++ map update example
This example program has a key value pair in a std::map as below.
1," Peter "
2," Lisa "
3," Danish "
4," Linda "The program will find the the value with given key e.g. 3 and update it with the value “John”.
As an output, this C++ Program will show the list before and after update value.
/*-------------------------------------------------------
* C++ Example - Update value in map
*
*/
#include <map> // Include map
#include <iostream>
using namespace std;
int main(){
/* Create a hash map - int as key and string as value */
std::map<int, std::string> m;
/* Insert some elements ( key value pair) in the hash map */
m.insert ( std::pair<int,string>(1,"Peter") );
m.insert ( std::pair<int,string>(2,"Lisa") );
m.insert ( std::pair<int,string>(3,"Danish") );
m.insert ( std::pair<int,string>(4,"Linda") );
/* Print the elements from hash map */
std::cout << "map Contains:\n";
std::map<int,string>::iterator itr;
for( itr = m.begin(); itr != m.end(); ++itr){
cout << "Key => " << itr->first << ", Value => " << itr->second.c_str() << endl;
}
/* Update the value of an existing key */
//updating the the value of key = 3
itr = m.find(3);
if (itr != m.end())
itr->second = "John";
std::cout << "Updated map Contains:\n";
for( itr = m.begin(); itr != m.end(); ++itr){
cout << "Key => " << itr->first << ", Value => " << itr->second.c_str() << endl;
}
return 0;
}
Output:
map Contains:
Key => 1, Value => Peter
Key => 2, Value => Lisa
Key => 3, Value => Danish
Key => 4, Value => Linda
Updated map Contains:
Key => 1, Value => Peter
Key => 2, Value => Lisa
Key => 3, Value => John
Key => 4, Value => Linda