> For the complete documentation index, see [llms.txt](https://42-guide.gitbook.io/42-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://42-guide.gitbook.io/42-guide/all-about-c++/file-handling.md).

# File Handling

**What Are File Streams?**

* **`std::ifstream`**: Used to read from files (input file stream).
* **`std::ofstream`**: Used to write to files (output file stream).

#### **Step-by-Step File Operations**

**A. Include Headers**

```cpp
#include <fstream>  // For file handling
#include <string>   // For std::string
```

**B. Reading a File (`std::ifstream`)**

```cpp
std::ifstream inputFile("data.txt");  // Open file

// Check if file opened successfully
if (!inputFile.is_open()) {
    std::cerr << "Error: Failed to open file!" << std::endl;
    return 1; // Exit with error code
}

// Read file line-by-line
std::string line;
while (std::getline(inputFile, line)) {
    std::cout << line << std::endl;
}

inputFile.close();  // Always close the file
```

**C. Writing to a File (`std::ofstream`)**

```cpp
std::ofstream outputFile("output.txt"); // Create/open file (overwrites by default)

if (!outputFile) { // Short error check
    std::cerr << "Error creating file!" << std::endl;
    return 1;
}

outputFile << "Hello, World!" << std::endl; // Write data
outputFile.close();
```

**D. File Opening Modes**

```cpp
// Append to existing file instead of overwriting
std::ofstream logFile("log.txt", std::ios::app);
```


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