• Arff File Python

Input/output with filesC provides the following classes to perform output and input of characters to/from files:.: Stream class to write on files.: Stream class to read from files.: Stream class to both read and write from/to files.These classes are derived directly or indirectly from the classes istream and ostream. We have already used objects whose types were these classes: cin is an object of class istream and cout is an object of class ostream. Therefore, we have already been using classes that are related to our file streams. And in fact, we can use our file streams the same way we are already used to use cin and cout, with the only difference that we have to associate these streams with physical files. Let's see an example.

Myfile.close;Once this member function is called, the stream object can be re-used to open another file, and the file is available again to be opened by other processes.In case that an object is destroyed while still associated with an open file, the destructor automatically calls the member function close.Text filesText file streams are those where the ios::binary flag is not included in their opening mode. These files are designed to store text and thus all values that are input or output from/to them can suffer some formatting transformations, which do not necessarily correspond to their literal binary value.Writing operations on text files are performed in the same way we operated with cout.

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Streampos size;streampos is a specific type used for buffer and file positioning and is the type returned by file.tellg. Values of this type can safely be subtracted from other values of the same type, and can also be converted to an integer type large enough to contain the size of the file.These stream positioning functions use two particular types: streampos and streamoff. These types are also defined as member types of the stream class:TypeMember typeDescriptionDefined as.It can be converted to/from and can be added or subtracted values of these types.It is an alias of one of the fundamental integral types (such as int or long long).Each of the member types above is an alias of its non-member equivalent (they are the exact same type). It does not matter which one is used. The member types are more generic, because they are the same on all stream objects (even on streams using exotic types of characters), but the non-member types are widely used in existing code for historical reasons.Binary filesFor binary files, reading and writing data with the extraction and insertion operators ( ) and functions like getline is not efficient, since we do not need to format any data and data is likely not formatted in lines.File streams include two member functions specifically designed to read and write binary data sequentially: write and read. The first one ( write) is a member function of ostream (inherited by ofstream). And read is a member function of istream (inherited by ifstream).

Objects of class fstream have both. Their prototypes are:write ( memoryblock, size );read ( memoryblock, size );Where memoryblock is of type char. (pointer to char), and represents the address of an array of bytes where the read data elements are stored or from where the data elements to be written are taken. The size parameter is an integer value that specifies the number of characters to be read or written from/to the memory block. 123file.seekg (0, ios::beg);file.read (memblock, size);file.close;At this point we could operate with the data obtained from the file. But our program simply announces that the content of the file is in memory and then finishes.Buffers and SynchronizationWhen we operate with file streams, these are associated to an internal buffer object of type streambuf. This buffer object may represent a memory block that acts as an intermediary between the stream and the physical file.

Arff File Python

For example, with an ofstream, each time the member function put (which writes a single character) is called, the character may be inserted in this intermediate buffer instead of being written directly to the physical file with which the stream is associated.The operating system may also define other layers of buffering for reading and writing to files.When the buffer is flushed, all the data contained in it is written to the physical medium (if it is an output stream). This process is called synchronization and takes place under any of the following circumstances:. When the file is closed: before closing a file, all buffers that have not yet been flushed are synchronized and all pending data is written or read to the physical medium. When the buffer is full: Buffers have a certain size. When the buffer is full it is automatically synchronized. Explicitly, with manipulators: When certain manipulators are used on streams, an explicit synchronization takes place. These manipulators are: and.

Explicitly, with member function sync: Calling the stream's member function sync causes an immediate synchronization. This function returns an int value equal to -1 if the stream has no associated buffer or in case of failure. Otherwise (if the stream buffer was successfully synchronized) it returns 0.