Question

We can add two string class object let’s say

string str1="hello"
string str2="world"

string final =str1+str2;

or

string f=str1.append(str2);

What is the difference between these two methods??
order in which they add or implementation or anything else??

Answer 1

operator+ will add two strings together and generate a new string with the value. Where as append will take a string and concatenate to the end of your string.

#include <iostream>
#include <string>
using namespace std;

int main ()
{
  string str = "Writing";
  string str2= " a book";
  str.append(str2);                      
  cout << str << endl;  // "Writing a book"
  return 0;
}

Also, append has more features like only append a part of that string

#include <iostream>
#include <string>
using namespace std;

int main ()
{
  string str;
  string str2="Writing ";
  string str3="print 10 and then 5 more";

  // used in the same order as described above:
  str.append(str2);                       // "Writing "
  str.append(str3,6,3);                   // "10 "
  str.append("dots are cool",5);          // "dots "
  str.append("here: ");                   // "here: "
  str.append(10,'.');                     // ".........."
  str.append(str3.begin()+8,str3.end());  // " and then 5 more"
  str.append<int>(5,0x2E);                // "....."

  cout << str << endl;
  return 0;
}

More on append here.