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ROOT
Reference Guide |
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ROOT
Reference Guide |
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An interface to read from, or write to, a ROOT file, as well as performing other common operations.
Please refer to the documentation of TFile for the details related to how data and executable code can be stored in ROOT files.
RFile is a modern and minimalistic interface to ROOT files, both local and remote, that can be used instead of TFile when you only need basic Put/Get operations and don't need the more advanced TFile/TDirectory functionalities. It provides:
RFile doesn't cover the entirety of use cases covered by TFile/TDirectory/TDirectoryFile and is not a 1:1 replacement for them. It is meant to simplify the most common use cases by following newer standard C++ practices.
RFile handles ownership via smart pointers, typically std::unique_ptr.
When getting an object from the file (via RFile::Get) you get back a unique copy of the object. Calling Get on the same object twice produces two independent clones of the object. The ownership over that object is solely on the caller and not shared with the RFile. Therefore, the object will remain valid after closing or destroying the RFile that generated it. This also means that any modification done to the object are not reflected to the file automatically: to update the object in the file you need to write it again (via RFile::Overwrite).
RFile::Put and RFile::Overwrite are the way to write objects to the file. Both methods take a const reference to the object to write and don't change the ownership of the object in any way. Calling Put or Overwrite doesn't guarantee that the object is immediately written to the underlying storage: to ensure that, you need to call RFile::Flush (or close the file).
Even though there is no equivalent of TDirectory in the RFile API, directories are still an existing concept in RFile (since they are a concept in the ROOT binary format). However they are for now only interacted with indirectly, via the use of filesystem-like string-based paths. If you Put an object in an RFile under the path "path/to/object", "object" will be stored under directory "to" which is in turn stored under directory "path". This hierarchy is encoded in the ROOT file itself and it can provide some optimization and/or conveniences when querying objects.
For the most part, it is convenient to think about RFile in terms of a key-value storage where string-based paths are used to refer to arbitrary objects. However, given the hierarchical nature of ROOT files, certain filesystem-like properties are applied to paths, for ease of use: the '/' character is treated specially as the directory separator; multiple '/' in a row are collapsed into one (since RFile doesn't allow directories with empty names).
At the moment, RFile doesn't allow getting directories via Get, nor writing ones via Put (this may change in the future).
Opening an RFile (for writing) and writing an object to it:
Opening an RFile (for reading) and reading an object from it:
Classes | |
| struct | RRecreateOptions |
Public Types | |
| enum | EListKeyFlags { kListObjects = 1 << 0 , kListDirs = 1 << 1 , kListRecursive = 1 << 2 } |
Public Member Functions | |
| ~RFile () | |
| void | Close () |
| Flushes the RFile if needed and closes it, disallowing any further reading or writing. | |
| size_t | Flush () |
| Writes all objects and the file structure to disk. | |
| template<typename T> | |
| std::unique_ptr< T > | Get (std::string_view path) const |
| Retrieves an object from the file. | |
| std::optional< RKeyInfo > | GetKeyInfo (std::string_view path) const |
Retrieves information about the key of object at path, if one exists. | |
| RFileKeyIterable | ListKeys (std::string_view basePath="", std::uint32_t flags=kListObjects|kListRecursive) const |
Returns an iterable over all keys of objects and/or directories written into this RFile starting at path basePath (defaulting to include the content of all subdirectories). | |
| template<typename T> | |
| void | Overwrite (std::string_view path, const T &obj, bool backupPrevious=true) |
| Puts an object into the file, overwriting any previously-existing object at that path. | |
| void | Print (std::ostream &out=std::cout) const |
| Prints the internal structure of this RFile to the given stream. | |
| template<typename T> | |
| void | Put (std::string_view path, const T &obj) |
| Puts an object into the file. | |
Static Public Member Functions | |
| static std::unique_ptr< RFile > | Open (std::string_view path) |
| Opens the file for reading. | |
| static std::unique_ptr< RFile > | Recreate (std::string_view path, const RRecreateOptions &opts=RRecreateOptions()) |
| Opens the file for reading/writing, overwriting it if it already exists. | |
| static std::unique_ptr< RFile > | Update (std::string_view path) |
| Opens the file for updating, creating a new one if it doesn't exist. | |
Static Public Attributes | |
| static constexpr int | kMaxPathNesting = 1000 |
Private Types | |
| enum | PutFlags { kPutAllowOverwrite = 0x1 , kPutOverwriteKeepCycle = 0x2 } |
| Flags used in PutInternal() More... | |
Private Member Functions | |
| RFile (std::unique_ptr< TFile > file) | |
| TKey * | GetTKey (std::string_view path) const |
Given path, returns the TKey corresponding to the object at that path (assuming the path is fully split, i.e. | |
| void * | GetUntyped (std::string_view path, std::variant< const char *, std::reference_wrapper< const std::type_info > > type) const |
Gets object path from the file and returns an owning pointer to it. | |
| template<typename T> | |
| void | PutInternal (std::string_view path, const T &obj, std::uint32_t flags) |
| void | PutUntyped (std::string_view path, const std::type_info &type, const void *obj, std::uint32_t flags) |
Writes obj to file, without taking its ownership. | |
Private Attributes | |
| std::unique_ptr< TFile > | fFile |
Friends | |
| TFile * | Internal::GetRFileTFile (RFile &rfile) |
| void * | Internal::RFile_GetObjectFromKey (RFile &file, const RKeyInfo &key) |
#include <ROOT/RFile.hxx>
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private |
Flags used in PutInternal()
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explicitprivate |
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default |
| void RFile::Close | ( | ) |
| size_t RFile::Flush | ( | ) |
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inline |
Retrieves an object from the file.
path should be a string such that IsValidPath(path) == true, otherwise an exception will be thrown. See ValidateAndNormalizePath() for info about valid path names. If the object is not there returns a null pointer.
| std::optional< ROOT::Experimental::RKeyInfo > RFile::GetKeyInfo | ( | std::string_view | path | ) | const |
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private |
Given path, returns the TKey corresponding to the object at that path (assuming the path is fully split, i.e.
"a/b/c" always means "object 'c' inside directory 'b' inside directory 'a'"). IMPORTANT: path must have been validated/normalized via ValidateAndNormalizePath() (see RFile.cxx).
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nodiscardprivate |
Gets object path from the file and returns an owning pointer to it.
The caller should immediately wrap it into a unique_ptr of the type described by type.
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inline |
Returns an iterable over all keys of objects and/or directories written into this RFile starting at path basePath (defaulting to include the content of all subdirectories).
By default, keys referring to directories are not returned: only those referring to leaf objects are. If basePath is the path of a leaf object, only basePath itself will be returned. If basePath is the path of a directory, it won't appear in the listing. flags is a bitmask specifying the listing mode. If (flags & kListObjects) != 0, the listing will include keys of non-directory objects (default); If (flags & kListDirs) != 0, the listing will include keys of directory objects; If (flags & kListRecursive) != 0, the listing will recurse on all subdirectories of basePath (default), otherwise it will only list immediate children of basePath.
Example usage:
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static |
Opens the file for reading.
path may be a regular file path or a remote URL.
| ROOT::RException | if the file at path could not be opened. |
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inline |
Puts an object into the file, overwriting any previously-existing object at that path.
The application retains ownership of the object.
If an object already exists at that path, it is kept as a backup cycle unless backupPrevious is false. Note that even if backupPrevious is false, any existing cycle except the latest will be preserved.
Throws a RException if path is already the path of a directory. Throws a RException if the file was opened in read-only mode.
| void RFile::Print | ( | std::ostream & | out = std::cout | ) | const |
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inline |
Puts an object into the file.
The application retains ownership of the object. path should be a string such that IsValidPath(path) == true, otherwise an exception will be thrown. See ValidateAndNormalizePath() for info about valid path names.
Throws a RException if path already identifies a valid object or directory. Throws a RException if the file was opened in read-only mode.
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inlineprivate |
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private |
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static |
Opens the file for reading/writing, overwriting it if it already exists.
| ROOT::RException | if a file could not be created at path (e.g. if the specified directory tree does not exist). |
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static |
Opens the file for updating, creating a new one if it doesn't exist.
| ROOT::RException | if the file at path could neither be read nor created (e.g. if the specified directory tree does not exist). |
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friend |
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friend |
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private |
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staticconstexpr |
