std::string::back() in C++ with Examples

Last Updated : 28 May, 2019

This function returns a direct reference to the last character of the string. This shall only be used on non-empty strings.
This can be used to access the last character of the string as well as to append a character at the end of the string. Length of the string remains unchanged after appending a character, last character of string gets replaced by the new one

Syntax

string str ("GeeksforGeeks");

Accessing last character
char end_char = str.back();

Appending character at end of string
str.back() = '#';

Parameter: This function takes no parameter

Return value: A reference to the last character in the string

Exception: If the string is empty it shows undefined behavior.

Below examples illustrate the use of the above method:

Program 1:

// C++ program to demonstrate 
// the use of the above method 
  
#include <iostream> 
  
// for std::string::back 
#include <string> 
  
using namespace std; 
  
int main() 
{ 
    string str("GeeksforGeeks"); 
  
    // Accessing last character of string 
    char end_char = str.back(); 
  
    cout << "Last character of string = "
         << end_char << endl; 
  
    // Appending a character to 
    // the end of string 
    str.back() = '#'; 
  
    cout << "New string = " << str << endl; 
  
    return 0; 
} 

Output:

Last character of string = s
New string = GeeksforGeek#

Program 2: It shows undefined behavior when the string is empty.

// C++ program to demonstrate 
// the use of the above method 
  
#include <iostream> 
  
// for std::string::front 
#include <string> 
  
using namespace std; 
  
int main() 
{ 
    string str(""); // Empty string 
  
    // trying to access last character 
    // of an empty string 
    char end_char = str.back(); 
  
    cout << "Last character of string = "
         << end_char << endl; 
  
    // Appending a character to 
    // the end of an empty string 
    str.back() = '#'; 
  
    cout << "New string = " << str << endl; 
  
    return 0; 
} 

Output:

Last character of string = 
New string = ÉGÃ@·ùþ?aPé£Îý@?k¯ÃÿÿÿÿÿÿÿXé£Îýÿÿÿ
@Ï?¨Õ,Ä @Pé£ÎýÏ??Á±?ðÏ?Ø%Bð3ÇGÃ¸ÂEÃ:µ# @Pé£ÎýI@Hé£Îýªÿ£Îý!P·Îýÿû?d@@8    ÀFÃ     @éé
éé©ê£ÎýÑÿ£Îý¹ê£Îý¾·ùþ?aDdCâ?gCx86_64

Reference: std::string::back()