C++ Standard Library <string>

The C++ Standard Library (Standard Template Library, STL) is one of the core components of C++, providing rich data structures and algorithms.

<string>It is the header file in the C++ Standard Library used for handling strings.

In C++, a string is a sequence of characters.<string>The header file providesstd::stringIt is a class that encapsulates C-style strings, providing safer and easier-to-use string manipulation functionality.

To use in a C++ program<string>the library, you first need to include this header file:

#include <iostream>
#include <string>

Basic Syntax

std::stringThe basic syntax of the class is as follows:

Declare a string variable:
```
std::string str;
```
Initialize string:
```
std::string str = "Hello, World!";
```

Usage+Concatenate strings:

std::string str1 = "Hello, ";
std::string str2 = "World!";
std::string result = str1 + str2;

Common member functions

std::stringThe class provides many member functions for manipulating strings. The following are some commonly used member functions:

size(): Returns the length of the string.
empty(): Checks whether the string is empty.
operator[]Access a character in the string by index.
substr(): Gets a substring.
find()Find the position of a substring in the main string.
replace(): Replaces some characters in the string.

Example

Below is a simple example using the<string>library, including the output results:

Example

#include <iostream>
#include <string>

int main() {
// Declare and initialize a string
std::string greeting = "Hello, World!";
std::cout << "Greeting: " << greeting << std::endl;

// Use size() to get the string length
std::cout << "Length of the greeting: " << greeting.size() << std::endl;

// Use empty() to check if the string is empty
std::cout << "Is the greeting empty? " << (greeting.empty() ? "Yes" : "No") << std::endl;

// Use operator[] to access a character at a specific position
std::cout << "Character at position 7: " << greeting[7] << std::endl;

// Use substr() to get a substring
std::string sub = greeting.substr(7, 5);
std::cout << "Substring from position 7 with length 5: " << sub << std::endl;

// Use find() to find a substring
std::cout << "Position of 'World' in the greeting: " << greeting.find("World") << std::endl;

// Use replace() to replace part of the string
// Replace 'World' with 'C++'
std::string modified = greeting;
std::string::size_type pos = modified.find("World");
if (pos != std::string::npos) {
modified.replace(pos, 5, "C++"); // Starting from position pos, replace 5 characters with "C++"
}
std::cout << "Modified greeting: " << modified << std::endl;

return 0;
}

Output:

Length of the greeting: 13
Is the greeting empty? No
Character at position 7: W
Substring from position 7 with length 5: World
Position of 'World' in the greeting: 7
Modified greeting: Hello, C++!

std::string member function summary table

The following is a summary of common std::string member functions:

Function Name	Description	Example code
`size()`	Returns the length of the string (the number of characters).	`std::cout << str.size();`
`length()`	and`size()`Same, returns the length of the string.	`std::cout << str.length();`
`empty()`	Determines whether the string is empty.	`std::cout << (str.empty() ? "Yes" : "No");`
`operator[]`	Accesses the character at a specified position in the string.	`std::cout << str[0];`
`at()`	Access the character at a specified position in the string (with bounds checking).	`std::cout << str.at(0);`
`substr()`	Return a substring starting from the specified position.	`std::string sub = str.substr(0, 5);`
`find()`	Find the position of a substring in the string.	`std::cout << str.find("sub") << std::endl;`
`rfind()`	Find the position of a substring starting from the end of the string.	`std::cout << str.rfind("sub") << std::endl;`
`replace()`	Replaces part of the content in the string.	`str.replace(pos, length, "new_substring");`
`append()`	Adds content at the end of the string.	`str.append(" more");`
`insert()`	Inserts content at a specified position.	`str.insert(pos, "inserted");`
`erase()`	Delete the character or substring at the specified position.	`str.erase(pos, length);`
`clear()`	Clear the string.	`str.clear();`
`c_str()`	Return a C-style string (null-terminated).	`const char* cstr = str.c_str();`
`data()`	Return a pointer to the character data (C++11 and later).	`const char* data = str.data();`
`compare()`	Compares two strings.	`int result = str.compare("other");`
`find_first_of()`	Find the position of the first character that matches any of the specified characters.	`size_t pos = str.find_first_of("aeiou");`
`find_last_of()`	Find the position of the last character that matches any of the specified characters.	`size_t pos = str.find_last_of("aeiou");`
`find_first_not_of()`	Find the position of the first character that does not match any of the specified characters.	`size_t pos = str.find_first_not_of("aeiou");`
`find_last_not_of()`	Find the position of the last character that does not match any of the specified characters.	`size_t pos = str.find_last_not_of("aeiou");`

Example

#include <iostream>
#include <string>

int main() {
std::string str = "Hello, World!";

// size()
std::cout << "Length: " << str.size() << std::endl;

// empty()
std::cout << "Is empty? " << (str.empty() ? "Yes" : "No") << std::endl;

// operator[]
std::cout << "First character: " << str[0] << std::endl;

// at()
std::cout << "Character at position 7: " << str.at(7) << std::endl;

// substr()
std::string sub = str.substr(7, 5);
std::cout << "Substring from position 7 with length 5: " << sub << std::endl;

// find()
size_t pos = str.find("World");
std::cout << "Position of 'World': " << pos << std::endl;

// replace()
str.replace(pos, 5, "C++");
std::cout << "Modified string: " << str << std::endl;

// append()
str.append(" How are you?");
std::cout << "Appended string: " << str << std::endl;

// insert()
str.insert(7, " Beautiful");
std::cout << "String after insert: " << str << std::endl;

// erase()
str.erase(7, 10);
std::cout << "String after erase: " << str << std::endl;

// clear()
str.clear();
std::cout << "String after clear: " << (str.empty() ? "Empty" : "Not empty") << std::endl;

// c_str()
str = "Hello, C++!";
const char* cstr = str.c_str();
std::cout << "C-style string: " << cstr << std::endl;

// compare()
int cmp = str.compare("Hello, C++!");
std::cout << "Comparison result: " << cmp << std::endl;

// find_first_of()
size_t pos_first_vowel = str.find_first_of("aeiou");
std::cout << "First vowel at position: " << pos_first_vowel << std::endl;

// find_last_of()
size_t pos_last_vowel = str.find_last_of("aeiou");
std::cout << "Last vowel at position: " << pos_last_vowel << std::endl;

// find_first_not_of()
size_t pos_first_non_vowel = str.find_first_not_of("aeiou");
std::cout << "First non-vowel at position: " << pos_first_non_vowel << std::endl;

// find_last_not_of()
size_t pos_last_non_vowel = str.find_last_not_of("aeiou");
std::cout << "Last non-vowel at position: " << pos_last_non_vowel << std::endl;

return 0;
}

Output:

Length: 13
Is empty? No
First character: H
Character at position 7: W
Substring from position 7 with length 5: World
Position of 'World': 7
Modified string: Hello, C++!
Appended string: Hello, C++! How are you?
String after insert: Hello,  BeautifulC++! How are you?
String after erase: Hello, C++! How are you?
String after clear: Empty
C-style string: Hello, C++!
Comparison result: 0
First vowel at position: 1
Last vowel at position: 4
First non-vowel at position: 0
Last non-vowel at position: 10

other extensions