String Functions in C++

String is a sequence of characters used to represent and manipulate text data efficiently. The C++ Standard Library provides the std::string class, which offers powerful built-in functionality for string operations.

• Strings store and manage sequences of characters dynamically in memory.
• std::string provides a rich set of built-in functions for manipulation and computation.
• These functions simplify tasks like searching, modifying, comparing, and processing text.

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

int main() {

    // Creating a string
    string str = "Hello World";

    // Display original string
    cout << "Original String: " << str << endl;

    // Find length of string
    cout << "Length: " << str.length() << endl;

    // Append text
    str.append(" !!!");
    cout << "After Append: " << str << endl;

    // Access character
    cout << "First Character: " << str[0] << endl;

    // Find a word
    cout << "Position of World: " << str.find("World") << endl;

    return 0;
}

Original String: Hello World
Length: 11
After Append: Hello World !!!
First Character: H
Position of World: 6

Standard String Class in C++

The std::string class in C++ (introduced in C++98) provides a standard and efficient way to represent and manipulate text data. It is defined in the <string> header file and supports a wide range of built-in string operations.

• std::string is used for dynamic management of character sequences in C++.
• It provides built-in functions for operations like find, replace, concatenate, and compare.
• It is a safer and more flexible alternative to traditional C-style character arrays.

Commonly Used String Functions in C++

String Length - length() or size()

In C++, the length of a string can be determined using either the length() or size() member function of the std::string class. Both functions work identically and return the total number of characters present in the string.

• These functions are used to count the number of characters in a string.
• They do not take any parameters.
• Both return the length of the string as an integer value.

Syntax

str.length();

str.size();

• Parameters: This function does not take any parameter.
• Return Value: Returns the number of characters in the string object.

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

int main() {
    string text = "GeeksforGeeks";
    
    cout << "String: " << text << endl;
    cout << "Length using length(): " << text.length() << endl;
    cout << "Length using size(): " << text.size() << endl;

    return 0;
}

String: GeeksforGeeks
Length using length(): 13
Length using size(): 13

Accessing Characters - at()

In C++, characters of a string can be accessed using the array subscript operator ([]) or the at() function provided by the std::string class. The at() function is preferred in many cases because it performs bounds checking and helps avoid invalid memory access.

• at() is used to access a character at a specific position in a string.
• It performs range checking and throws an exception if the index is out of bounds.
• It provides a safer alternative to the [] operator.

Syntax

str.at(index);

• Parameters: index - Position of the character in the string, starting from 0.
• Return Value: Returns the character present at the specified index.

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

int main() {
    string text = "GeeksforGeeks";
    
    cout << "String: " << text << endl;
    cout << "Character at index 3: " << text.at(3) << endl;

    return 0;
}

String: GeeksforGeeks
Character at index 3: k

Concatenating Strings - append() or + Operator

In C++, strings can be concatenated using either the + operator or the append() function provided by the std::string class. Both methods are commonly used to join two or more strings into a single string.

• The + operator provides a simple and readable way to combine strings.
• The append() function offers more control and flexibility for concatenation.
• Both methods modify or create a new string containing the combined result.

1. + Operator

The + operator is overloaded in the std::string class to support string concatenation. It joins two strings and returns a new combined string.

Syntax

str1 + str2;

The + operator is used to concatenate two strings. The resulting string fullName will be "GeeksforGeeks Hello".

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

int main() {
    string str1 = "GeeksforGeeks";
    string str2 = " Hello";

    string fullName = str1 + str2;

    cout << "Concatenated String: " << fullName << endl;

    return 0;
}

Concatenated String: GeeksforGeeks Hello

2. append() Function

The append() function is a member function of std::string used to add one string to the end of another.

Syntax

str1.append(str2);

• Parameters: string2 - The string to be append, which can be either a C-style string or a C++ string.
• Return Value: Reference to the final string.

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

int main() {
    string str1 = "GeeksforGeeks";
    string str2 = " Hello";

    str1.append(str2);

    cout << "Concatenated String: " << str1 << endl;

    return 0;
}

Concatenated String: GeeksforGeeks Hello

String Comparison - compare() or == Operator

In C++, strings can be compared using either the == operator or the compare() function of the std::string class. Both methods are used to check equality or lexicographical order between two strings.

• The == operator provides a simple way to check if two strings are equal.
• The compare() function gives detailed comparison results based on lexicographical order.
• Both methods are commonly used depending on whether a boolean or numeric result is needed.

1. == Operator

The equality operator (==) is overloaded in the std::string class to compare two strings for equality.

Syntax

str1 == str2;

This returns true if both strings are equal, otherwise it returns false.

• Parameters: None
• Return Value: Returns true if strings are equal and false if strings are not equal

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

int main() {
    string str1 = "Hello";
    string str2 = "Hello";

    if (str1 == str2)
        cout << "Strings are equal";
    else
        cout << "Strings are not equal";

    return 0;
}

Strings are equal

2. compare() Function

The compare() function is a member function of std::string used for lexicographical comparison between strings.

Syntax

str1.compare(str2);

Parameters: str2 - The string to be compared; it can be a C-style or C++ string.

Return Value

• Returns 0 if both strings are equal.
• Returns a value > 0 if str1 is greater than str2.
• Returns a value < 0 if str1 is less than str2.

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

int main() {
    string str1 = "Apple";
    string str2 = "Banana";

    int result = str1.compare(str2);

    cout << "Result: " << result;

    return 0;
}

Result: -1

Searching -  find()

The find() function in C++ is used to search for a character or substring inside a string. It returns the position of the first occurrence if the element is found.find() function of the std::string class to check whether a given character or a substring is present in the string or a part of string.

Syntax:

str.find(var);

Parameters: var - It can be a C style string, C++ style string, or a character that is to be searched in the string.

Return Value

• Returns the index (position) of the first occurrence of the character or substring.
• If not found, it returns std::string::npos..

The position variable will contain 4, which is the starting index of the first occurrence of "Programming" in the string text.

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

int main() {
    string text = "C++ Programming";

    size_t position = text.find("Programming");

    cout << "Position: " << position;

    return 0;
}

Position: 4

Generate Substring - substr()

The substr() function in C++ is used to extract a portion of a string and return it as a new std::string object. It is a member function of the std::string class.

Syntax

str.substr(start, length);

Parameters

• start: Starting position of the substring to be generated.
• length: Number of characters to include in the substring

Return Type Returns a new std::string object containing the extracted substring

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

int main() {
    string text = "Hello World";

    string sub = text.substr(6, 5);

    cout << "Substring: " << sub;

    return 0;
}

Substring: World

Modifying Strings

C++ provides several member functions in the std::string class to modify existing strings efficiently.

• These functions allow insertion, replacement, and updating parts of a string.
• They directly modify the original string object.
• They are useful for dynamic text editing and manipulation tasks.

insert()

The insert() function is used to insert a string at a specified position within an existing string.

Syntax

str1.insert(index, str2);

Parameters

• str2: string to be inserted.
• index: position of where to insert the new string

Return Type: Returns a reference to the modified string (str1)

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

int main() {
    string str1 = "GeeksGeeks";
    string str2 = "for";

    str1.insert(5, str2);

    cout << "Updated String: " << str1;

    return 0;
}

Updated String: GeeksforGeeks

replace()

The replace() function replaces the part of the string with the given other string. Unlike insert, the characters in the part where the new string is to be inserted are removed.

Syntax

str1.replace(index, size, str2);

Parameters

• index: Index of where to start replacing the new string.
• size: length of the part of the string that is to be replaced.
• str2: new string that is to be inserted.

Return Type: Returns a reference to the modified string (str1)

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

int main() {
    string str1 = "I love Java";
    string str2 = "C++";

    str1.replace(7, 4, str2);

    cout << "Updated String: " << str1;

    return 0;
}

Updated String: I love C++

3. erase()

The erase() function is a member function of std::string class that is used to remove a character or a part of the string.

Syntax

str1.erase(start, end);

Parameters

• start: Starting position of the portion to be removed
• end: Ending position (number of characters or range depending on usage)

Return Type: Returns a reference to the modified string (str1)

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

int main() {
    string str1 = "Hello World";

    str1.erase(5, 6);

    cout << "Updated String: " << str1;

    return 0;
}

Updated String: Hello

Converting std::string to C-Style String – c_str()

The c_str() function is a member of the std::string class used to convert a C++ string into a C-style string (null-terminated character array). It is commonly used when working with C library functions that require character pointers.

• It returns a pointer to a null-terminated character array.
• It is useful for compatibility with legacy C APIs.
• It does not modify the original string.

Syntax

str.c_str();

Parameters: This function does not take any parameter.

Return Value: Returns a pointer to a null-terminated character array equivalent of the string

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

int main() {
    string str = "Hello World";

    const char* cstr = str.c_str();

    cout << "C-style string: " << cstr;

    return 0;
}

C-style string: Hello World

Standard String Operations in C++ (std::string)

The std::string class provides a rich set of built-in functions for performing common string operations. The table below summarizes the most frequently used functions.

Note: The above functions only works for C++ Style strings (std::string objects) not for C Style strings (array of characters).