how to remove a index from a string in cpp

// CPP code to illustrate
// erase(size_type idx, size_type len )
#include <iostream>
#include <string>
using namespace std;
 
// Function to demo erase
void eraseDemo(string str)
{
    // Deletes 4 characters from index number 1
    str.erase(1, 4);
 
    cout << "After erase : ";
    cout << str;
}
 
// Driver code
int main()
{
    string str("Hello World!");
 
    cout << "Before erase : ";
    cout << str << endl;
    eraseDemo(str);
 
    return 0;
}