cpp std::string

cpp/c++ std::string

let's see cpp code first

Let's see c++ code first

Code

#include <iostream>
#include <string>

int main()
{
	std::string str = "This is a string";
	std::cout << str << '\n' << str.size() << std::endl;

	str = "A string";
	std::cout << str << std::endl << str.size() << "\n";
}

analysis

cpp string

You have learned from day-02 that you can print a string using std::cout:

std::cout << "Hello World c++!" << std::endl;

The c++ string is sent to operator<< as its second parameter, and printed with std::cout . What is operator<< ? it has been explained at day-02 too.

std::string

Blow

Did you have thought a question: How to code if I want to save a string at some place in the program instead of printing the string?

std::string is the answer, it can create an object, and store the string into the object, without printing the string immediately.

Blow

std::string str = "This is a string";

In this line, create an object named str using std::string, and then store "This is a string" into the str .

Object - Like std::cout, which is an object; str is an object too. One difference of them is that the object std::cout is already created by the c++ system, but the object str is created by you.

variable - str is an object, it has a name: str, we can also call it a variable.

Initialize - Just like this line, when storing value on the same sentence as the variable is created, we call it initialize.

You can also create an object or variable without initializing:

std::string str2;

Blow

str = "A string";

The str has already stored with a string "This is a string". By this line, the old stored string will be cleared and str will be stored with a new string: "A string" .

Assignment - Just like this line, when storing value on a variable which has already been created previously, we call it assignment.

Blow

std::cout << str;

You have learned from day-02 that many objects and many values can be passed to operator<< as the second parameter and printed with std::cout, the objects created by std::string can be too.

Blow

str.size();
std::cout << str.size();

See str.size(), that means we call a method .size() from the object str, the calling will return an integer value to tell us how many characters that the string has which the object stored.

It requires that, the object has a method .size(), in other words, the class std::string has already defined the method .size() .

Header

#include <string>

std::string is declared and defined in a file on your disk: string .

Last

This article only has three points, please don't feel stress:

Written on Aug 03, 2024

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