TFile

TFile is a core class in the ROOT data analysis framework used to read from and write to ROOT files, the framework’s standard on-disk container for persistent objects. ROOT files typically have the .root extension and are used to store complex scientific data, including trees, histograms, and custom C++ objects, in a hierarchical structure.

TFile acts as a wrapper around a binary container that holds a directory-like organization of objects. Objects stored in a TFile are serialized by ROOT’s I/O system and indexed by keys, which record metadata such as the object name, class, size, and a timestamp. The file can be opened in various modes, including READ for reading existing files, RECREATE for creating new files (overwriting any existing content), UPDATE for modifying an existing file, and NEW for creating a file only if it does not exist.

Key features of TFile include support for optional data compression and integrated access to ROOT’s directory and key abstractions (such as TDirectory and TKey). Compression, when enabled, applies to the stored objects and can use algorithms supported by the ROOT build (for example, zlib), with selectable compression levels. TFile also provides convenient methods for writing objects to the file, retrieving objects by name, listing contained keys, and managing the file’s lifecycle (open, close, flush).

TFile is widely used in high-energy physics and other scientific fields that rely on ROOT for data analysis. While powerful within ROOT, ROOT files are not a general-purpose database format and require the ROOT environment to read or manipulate.