{"title":"Input / Output","description":null,"content":"# The Basics of I/O Streams\n\nIn C++, we primarily use **streams** to handle input and output. A stream is essentially a sequence of data elements made available over time. There are two main types of streams we'll work with:\n\n- **Input Streams**: Used for reading data into the program.\n- **Output Streams**: Used for sending data out of the program.\n\nThe C++ standard library provides a set of objects for stream handling, with the most common being `cin` for input and `cout` for output. \n\nHere’s a simple example that shows how to read input from the user and print it out:\n\n\n```cpp\n#include \nusing namespace std;\n\nint main() {\n int age;\n cout << \"Enter your age: \"; // Prompt user for input\n cin >> age; // Read input from user\n cout << \"Your age is \" << age << \" years.\" << endl; // Output the result\n return 0;\n}\n```\n\n\nIn this code, `cout` is used to display a prompt for the user, and `cin` reads the input. The `endl` manipulator is used to insert a newline and flush the output buffer.\n\n---\n\n# Formatting Output\n\nWhen we want our output to be more user-friendly, we often need to format it. C++ provides several ways to format output, including manipulators and the `iomanip` library.\n\n### Using Manipulators\n\nManipulators are convenient functions that alter the way data is presented. Here are a few commonly used manipulators:\n\n- `std::setw(n)`: Sets the width of the next output field to `n`.\n- `std::setprecision(n)`: Sets the number of digits to display after the decimal point.\n- `std::fixed`: Forces the output to use fixed-point notation.\n\nLet’s look at an example that demonstrates these manipulators:\n\n\n```cpp\n#include \n#include // Required for manipulators\nusing namespace std;\n\nint main() {\n double pi = 3.14159;\n cout << fixed << setprecision(2); // Set to fixed-point with 2 decimal places\n cout << \"Value of pi: \" << setw(10) << pi << endl; // Right-align output in a width of 10\n return 0;\n}\n```\n\n\nIn this code, `setprecision(2)` ensures that `pi` is displayed with two decimal places, and `setw(10)` makes the output occupy a field of 10 characters, aligning it to the right.\n\n---\n\n# Input from Different Data Types\n\nWhile reading input, it's essential to ensure the data type matches what you're expecting. C++ handles various data types, such as integers, floating-point numbers, and strings. \n\nHowever, there are some nuances when dealing with different types:\n\n- **Integers and Floats**: When you read a float and provide an integer value, C++ will automatically handle the conversion. But if you input a non-numeric string, it can lead to errors or unexpected behavior.\n- **Strings**: The standard `cin` will read input until it encounters whitespace. If you want to read an entire line, you should use `std::getline`.\n\nHere’s an example that handles both integers and strings:\n\n\n```cpp\n#include \n#include \nusing namespace std;\n\nint main() {\n string name;\n int age;\n\n cout << \"Enter your name: \";\n getline(cin, name); // Read an entire line for the name\n cout << \"Enter your age: \";\n cin >> age; // Read integer input for age\n \n cout << \"Hello, \" << name << \". You are \" << age << \" years old.\" << endl;\n return 0;\n}\n```\n\n\nThis code snippet illustrates how to read a full line for the name and an integer for the age. Using `getline` allows for spaces in the input, which is common in names.\n\n---\n\n# Error Handling in Input\n\nInput handling isn't just about reading data; it’s also about ensuring the data is valid. C++ provides mechanisms to check for errors during input operations.\n\nFor instance, if the input fails (e.g., the user types a letter when an integer is expected), the `cin` stream enters a \"fail\" state. We can check for this and take appropriate actions.\n\nHere’s how you can handle input errors:\n\n\n```cpp\n#include \nusing namespace std;\n\nint main() {\n int age;\n cout << \"Enter your age: \";\n \n while (!(cin >> age)) { // Check if the input is valid\n cout << \"Invalid input, please enter a number: \";\n cin.clear(); // Clear the fail state\n cin.ignore(numeric_limits::max(), '\\n'); // Ignore the rest of the line\n }\n\n cout << \"Your age is \" << age << \" years.\" << endl;\n return 0;\n}\n```\n\n\nIn this example, if the user enters invalid input, a message prompts them to enter a valid number. The `cin.clear()` function clears the error state, and `cin.ignore()` skips to the next line, allowing for new input.\n\n---\n\n# File Input and Output\n\nIn addition to standard input and output, C++ provides the ability to read from and write to files. This is essential for persistent data storage and retrieval.\n\nTo work with files, we use the `` library, which provides `ifstream` for input file streams and `ofstream` for output file streams.\n\nHere’s a simple example demonstrating file output:\n\n\n```cpp\n#include \n#include \nusing namespace std;\n\nint main() {\n ofstream outFile(\"output.txt\"); // Create an output file stream\n if (!outFile) {\n cerr << \"Error creating file!\" << endl;\n return 1; // Exit if file cannot be created\n }\n\n outFile << \"Hello, File!\" << endl; // Write to the file\n outFile.close(); // Close the file\n\n cout << \"Data written to output.txt\" << endl;\n return 0;\n}\n```\n\n\nIn this code, we create an output file stream to write to `output.txt`. Always remember to check if the file opened successfully, and don't forget to close the file when you're done.\n\nFor reading from a file, the process is similar. Here’s how you can read from the file created above:\n\n\n```cpp\n#include \n#include \n#include \nusing namespace std;\n\nint main() {\n ifstream inFile(\"output.txt\"); // Create an input file stream\n if (!inFile) {\n cerr << \"Error opening file!\" << endl;\n return 1; // Exit if file cannot be opened\n }\n\n string line;\n while (getline(inFile, line)) { // Read lines from the file\n cout << line << endl; // Output the lines to console\n }\n\n inFile.close(); // Close the file\n return 0;\n}\n```\n\n\nThis snippet reads from the `output.txt` file line by line and prints each line to the console. This is a common approach for processing text files.","pageType":"cpp"}

Input / Output

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