C++ Standard Library: iostream and File Operations
The C++ Standard Library provides powerful input and output (I/O) capabilities, among which <span>iostream</span> is one of the most commonly used classes. Through <span>iostream</span>, we can perform basic console input and output, while file operations allow us to handle data more flexibly.
Overview of iostream
<span>iostream</span> is a set of classes used for handling input and output, including <span>istream</span>, <span>ostream</span>, and their combination <span>iostream</span>.
- istream: Used for input streams, such as reading data from the keyboard.
- ostream: Used for output streams, such as printing information to the screen.
- iostream: A stream that supports both input and output.
1. Using cout to Output to Console
Here is a simple example demonstrating how to use <span>cout</span> to output text:
#include <iostream>
int main() { std::cout << "Hello, world!" << std::endl; return 0;}In this code:
- We include the
<span><iostream></span>header file to use the standard I/O classes. - We use
<span>std::cout</span>to print a string to the console, followed by a newline character.
2. Using cin to Read User Input from Console
Next, let’s look at how to receive user input from the console:
#include <iostream>
#include <string>
int main() { std::string name;
std::cout << "请输入你的名字: "; std::cin >> name;
std::cout << "你好, " << name << "!" << std::endl;
return 0;}In the above code:
- We first define a string variable to store the user’s name.
- We use
<span>std::cin</span>to receive input from the keyboard and store it in the variable.
Overview of File Operations
The C++ Standard Library also provides methods for reading and writing files. This is mainly implemented through the <span>fstream</span>, <span>ifstream</span>, and <span>ofstream</span> classes.
Here is a brief description of each class:
- ifstream: Input file stream, used for reading file contents.
- ofstream: Output file stream, used for writing content to files.
- fstream: File stream that can perform both read and write operations.
3. Creating and Writing to a File (ofstream)
Below is an example demonstrating how to create a new file and write content to it:
#include <fstream>
#include <string>
int main() { std::ofstream outFile("example.txt");
if (outFile.is_open()) { outFile << "这是第一行。\n"; outFile << "这是第二行。" << std::endl; outFile.close(); // Close the file after writing std::cout << "成功写入到example.txt" << std::endl; } else { std::cerr << "无法打开或创建example.txt" << std::endl; }
return 0;}In this code:
- We use a new text file named
<span>"example.txt"</span>. If the file does not exist, it will be created automatically. - After checking if it opened successfully, we write some text to the document and finally close it to save the changes.
4. Reading from a File (ifstream)
Now, this example demonstrates how to read content from the previously created data:
#include <fstream>
#include <string>
#include <iostream>
int main() { std::ifstream inFile("example.txt");
if (inFile.is_open()) { std::string line;
while (std::getline(inFile, line)) { // Read line by line std::cout << line + "\n"; // Print each line }
inFile.close(); // Close the file after completion } else { std::cerr << "无法打开example.txt" << std::endl; }
return 0; }In this code:
- We attempt to open the previously created
<span>"example.txt"</span>file for reading information. If successful, it reads and prints its content line by line to the console.
Conclusion
Today, we learned the basic I/O operations in the C++ Standard Library, including basic interactions with the console and simple reading/writing of text data on disk. With these fundamentals mastered, you can further explore more complex data structures and algorithms while leveraging C++’s rich and efficient data processing capabilities. We hope this tutorial helps you successfully start your programming journey.