Strings in C++

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.

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.

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).

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).

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.

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.

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).

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.

"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:

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