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Strings in C++

Last Updated : 20 Sep, 2025
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Strings in C++ are objects of the std::string class. They are used to represent and manipulate sequences of characters.

  • Unlike C-style character arrays (char[]), std::string handles memory management automatically and provides a wide range of built-in functions for ease of use.
  • Can automatically grow and shrink as you add or remove characters, unlike fixed-size C-style strings.
  • You can easily access characters, join strings, compare them, extract substrings, and search within strings using built-in functions.
C++ 
#include <iostream> #include <string> using namespace std; int main() {    // Creating a string  string str = "Hello Geeks";  // Traversing using index  cout << "Using index: ";  for (int i = 0; i < str.size(); i++) {  cout << str[i] ;  }  cout << endl;  // Traversing using range-based for loop  cout << "Using range-based for loop: ";  for (char ch : str) {  cout << ch ;  }  cout << endl;  // Traversing using iterator  cout << "Using iterator: ";  for (auto it = str.begin(); it != str.end(); it++) {  cout << *it ;  }  cout << endl;  return 0; }

Output
Using index: Hello Geeks Using range-based for loop: Hello Geeks Using iterator: Hello Geeks

Syntax

The string container is defined as std::string class inside the <string> header file.

string str;

where,

  • string: Class provided by STL to handle sequences of characters.
  • str: Name assigned to the string object.

Basic Operations in String

Basic operations on Strings are shown below:

Initializing a String

  • Initialization of a string assigns characters to the string at the time of creation.
  • A string can be initialized directly using = or constructor syntax with text inside quotes.
C++ 
#include <iostream> #include <string> using namespace std; int main() {    // Initializing a string directly  string str = "Hello Geeks";  // Printing the string  cout << str << endl;  return 0; }

Output
Hello Geeks

Accessing Characters

  • Characters of a string can be accessed using the [] operator or the .at() function.
  • Time complexity for accessing characters is O(1).
C++ 
#include <iostream> #include <string> using namespace std; int main() {  string str = "Hello Geeks";  // Access using index operator []  cout << "First character: " << str[0] << endl;  cout << "Fifth character: " << str[4] << endl;  // Access using at()  cout << "Character at index 6: " << str.at(6) << endl;  return 0; }

Output
First character: H Fifth character: o Character at index 6: G

String Length

  • The number of characters in a string can be found using size() or length().
  • Time complexity to find string length is O(1).
C++ 
#include <iostream> #include <string> using namespace std; int main() {  string str = "Hello Geeks";  // Using size()  cout << "Length using size(): " << str.size() << endl;  // Using length()  cout << "Length using length(): " << str.length() << endl;  return 0; }

Concatenation of Strings

  • Strings can be joined using the + operator or the append() function.
  • The + operator creates a new string, while append() modifies the existing string in place.
  • Time complexity for concatenation is O(n+m), where n is the size of string and m is the size of the string to be concatenated.
C++ 
#include <iostream> #include <string> using namespace std; int main() {  string str1 = "Hello";  string str2 = " Geeks";  // Using + operator  string result1 = str1 + str2;  cout << "Concatenation using + : " << result1 << endl;  // Using append() function  string result2 = str1;  result2.append(str2);  cout << "Concatenation using append(): " << result2 << endl;  return 0; }

Output
Concatenation using + : Hello Geeks Concatenation using append(): Hello Geeks

Modifying a String

  • Characters of a string can be added with .push_back(), removed with .pop_back(), or altered using .insert() and .erase().
  • Time complexity for push/pop is O(1) and O(n) for insert/erase.
C++ 
#include <iostream> #include <string> using namespace std; int main() {  string str = "Hello Geeks";  // Adding a character at the end  str.push_back('!');  cout << "After push_back: " << str << endl;  // Removing the last character  str.pop_back();  cout << "After pop_back: " << str << endl;  // Inserting a substring  str.insert(5, " C++");  cout << "After insert: " << str << endl;  // Erasing part of the string  str.erase(5, 4);   cout << "After erase: " << str << endl;  return 0; }

Output
After push_back: Hello Geeks! After pop_back: Hello Geeks After insert: Hello C++ Geeks After erase: Hello Geeks

Substring Extraction

  • The .substr(pos,len) is used to extract a part of a string, where pos means the starting position and len means how many characters you want to copy.
  • This function creates a new string containing the selected portion, starting at pos and copying len characters.
  • Time complexity of extraction is O(len).
C++ 
#include <iostream> #include <string> using namespace std; int main() {  string str = "Hello Geeks";  // Extract "Hello"  string sub1 = str.substr(0, 5);   cout << "Substring 1: " << sub1 << endl;  // Extract "Geeks"  string sub2 = str.substr(6, 5);   cout << "Substring 2: " << sub2 << endl;  return 0; }

Output
Substring 1: Hello Substring 2: Geeks

Know more about Substring extraction in C++.

Searching in a String

  • The find() function is used to search for a substring inside a string. If found, it returns the index (position) where the substring starts; if not, it returns a special value (npos).
  • Time complexity to search is O(n*m), where n is the length of string and m is the substring length.
C++ 
#include <iostream> #include <string> using namespace std; int main() {  string str = "Hello Geeks";  size_t pos = str.find("Geeks");   if (pos < str.size()) {  cout << "\"Geeks\" found at index: " << pos << endl;  }  return 0; }

Output
"Geeks" found at index: 6

Learn more about find() in C++

C++ String Functions

C++ provides some inbuilt functions which are used for string manipulation, such as the strcpy() and strcat() functions for copying and concatenating strings. Some of them are:

Function

Description

length()

This function returns the length of the string.

swap() 

This function is used to swap the values of 2 strings.

size()

Used to find the size of string

resize()

This function is used to resize the length of the string up to the given number of characters.

find()

Used to find the string which is passed in parameters

push_back()

This function is used to push the passed character at the end of the string

pop_back()

This function is used to pop the last character from the string

clear()

This function is used to remove all the elements of the string.

strncmp()

This function compares at most the first num bytes of both passed strings.

strncpy()

This function is similar to strcpy() function, except that at most n bytes of src are copied

strrchr()

This function locates the last occurrence of a character in the string.

strcat()

This function appends a copy of the source string to the end of the destination string

find()

This function is used to search for a certain substring inside a string and returns the position of the first character of the substring. 

replace()

This function is used to replace each element in the range [first, last) that is equal to old value with new value.

substr()

This function is used to create a substring from a given string.

compare()

This function is used to compare two strings and returns the result in the form of an integer.

erase()

This function is used to remove a certain part of a string.

rfind()

This function is used to find the string's last occurrence.

These functions are discussed in this article in more detail - String Function in C++


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