Difference between + operator and append function for string class object in c++?

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.

Answer 2

Well, obviously str1 has different values between the two operations (in the first, it remains the same as before, in the second it has the same value as f).

Another difference is str1 + str2 creates a temporary string (the result of the concatenation) and then applies operator=. The str1.append() call does not create the temporary variable.

Answer 3

For one, operator+ creates a new string, whereas append modifies a previously existing one. So, in your examples, the second one will modify str1, and the first one will not. The append method is closer to += than to +.