How to Use std::string in C++

3 min
Intermediate

In C++, the std::string class is a utility of the standard library that represents and manages strings of characters.

Unlike traditional C character arrays, std::string offers a series of methods and operators that facilitate text manipulation (such as concatenation, searching, and modifying substrings).

Additionally, std::string automatically manages memory, avoiding many of the problems associated with manual memory management.

Whenever possible, we should prefer std::string to a null-terminated string.

Declaration

The basic declaration of a string is:

#include <string>

std::string string_name;

For example, something like this,

#include <string>

std::string greeting;  // Empty string
std::string name = "Luis";  // Initialization with a literal string

Initialization

We can initialize the value of the std::string in different ways.

Literal string

std::string greeting = "Hello, world";

With constructor

std::string name(5, 'a');  // Initializes with 5 'a' characters, i.e., "aaaaa"

Basic operations

Concatenation

We can concatenate strings using the + operator

std::string name = "Luis";
std::string last_name = "Pérez";
std::string full_name = name + " " + last_name;  // "Luis Pérez"

Or even the += operator

std::string greeting = "Hello";
greeting += ", world";  // "Hello, world"

Characters

We can access a specific character using the [] operator

char first_character = greeting[0];  // 'H'

Or using the at method, which provides safe access (throws an exception if the index is out of bounds).

char first_character = greeting.at(0);  // 'H'

Modification

We can modify strings using both the [] operator and the at method

greeting[0] = 'h';  // "hello, world"
greeting.at(0) = 'H';  // "Hello, world"

Length

We can get the length using length or size

std::size_t length = greeting.length();  // 10

Comparison

To compare strings, we can use relational operators

if (name == "Luis") {
    std::cout << "The name is Luis" << std::endl;
}

Or the compare method

if (name.compare("Luis") == 0) {
    std::cout << "The name is Luis" << std::endl;
}

We can search for text within a string using find

std::size_t position = greeting.find("world");  // Returns 6

Substrings

We can obtain a substring using the substr method

std::string world = greeting.substr(6, 5);  // "world"

Methods and functions

append

Adds a string to the end of the current string.

greeting.append("!!");  // "Hello, world!!"

insert

Inserts a string at a specific position.

greeting.insert(5, "dear ");  // "Hello, dear world"

erase

Removes a part of the string.

greeting.erase(5, 7);  // "Hello, world"

replace

Replaces a part of the string with another.

greeting.replace(5, 5, "dear ");  // "Hello, dear world"

c_str

Returns a pointer to a C-style string (null-terminated).

const char* c_greeting = greeting.c_str();

empty

Checks if the string is empty.

if (greeting.empty()) {
    std::cout << "The string is empty" << std::endl;
}

clear

Clears the string, making it empty.

greeting.clear();

Practical example

Let’s see a somewhat more complete example to illustrate the use of std::string

#include <iostream>
#include <string>

int main() {
    std::string name = "Luis";
    std::string last_name = "Pérez";
    std::string full_name = name + " " + last_name;

    std::cout << "Full name: " << full_name << std::endl;

    // Modify the name
    full_name.replace(0, 4, "Carlos");

    std::cout << "Modified name: " << full_name << std::endl;

    // Search and remove last name
    std::size_t position = full_name.find("Pérez");
    if (position != std::string::npos) {
        full_name.erase(position);
    }

    std::cout << "Without last name: " << full_name << std::endl;

    return 0;
}

In this example, we see how to declare, initialize, concatenate, modify, search, and remove parts of a std::string.