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Master Modern C++

Working with File Streams

Explore how to use C++ file streams to read from and write to files, ensuring data persistence across program runs. Learn to verify file access, handle buffering with RAII for safe resource management, and distinguish between text and binary file modes. Gain practical skills to manage files reliably within your C++ applications.

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Up to this point, our programs have been transient. They run, produce output, then exit, and any state disappears with the process. Real software needs persistence so it can save configuration, store logs, and keep progress across runs. Files are one of the simplest ways to do that.

C++ keeps file I/O familiar by exposing files through streams, the same model you already used with std::cin and std::cout. Once a stream is connected to a file, reading and writing use the same tools you know. The key difference is that file streams must be opened successfully, and that can fail.

The file stream classes

File operations are provided by the <fstream> header. It defines three stream types:

  • std::ifstream is an input file stream. It inherits from std::istream and is used to read from files.

  • std::ofstream is an output file stream. It inherits from std::ostream and is used to write to files.

  • std::fstream is a combined stream. It inherits from std::iostream and can both read and write.

The ...