File Management in C++

File Management in C++

• File handling is a crucial part of any program.
• Applications often save and retrieve data from local storage (disk).
• Physical files reside on secondary storage.
• Logical files are created in RAM for program processing.
• Logical files are objects with file data types.
• A variable, often called a file handler, points to the logical file.
• C++ file I/O classes simplify file operations (read/write).

Streams and Files

• The I/O system provides a consistent interface to programmers, independent of the actual devices being accessed.
• This abstraction layer is called a stream.
• The actual device is called a file.
• C++ can handle various devices (terminals, disk drives, tape drives), treating them as logical streams.
• Streams are categorized as text or binary.

Text Streams

• A text stream is a sequence of characters.
• Character translations (like newlines converted to carriage return/linefeed pairs) might occur based on the host environment.
• There might not be a perfect one-to-one correspondence between characters written/read and those on the external device due to transformations.

Binary Streams

• A binary stream directly corresponds to bytes on the external device (no character translations).
• The number of bytes written/read matches the number on the external device.
• Implementation-defined null bytes might be appended to fill sectors, if needed.

Files in C++

• C++ files can be anything from disk files to terminals or printers.
• A stream is associated with a file through an "open" operation.
• Information exchange happens between the program and the open file.
• All streams are similar, but files can vary.
• If a file allows position requests, opening it initializes the file position indicator to the start of the file.

File Position Indicator

• The file position indicator increments after each character read/written.
• Dissociating a file from a stream uses a "close" operation.
• Closing an output file involves writing any pending contents (flushing).
• Files are automatically closed when a program finishes normally; abnormal termination might leave files open.

File Control Structure

• Stream-file associations have file control structures (type FILE).
• stdio.h defines this structure.

The File Pointer

• A file pointer points to file information (name, status, current position).
• It's used by the associated stream to control I/O operations.
• A file pointer is a variable of type FILE.

Standard Streams

• Three streams (stdin, stdout, stderr) open automatically when a program starts.
• They typically point to the console (for input/output/error).
• These streams are file pointers, used by ANSI C file system for console I/O operations.

C++ File I/O Classes and Functions

• To do file I/O, include the header fstream.h.
• fstream.h defines classes: ifstream (input), ofstream (output), fstream (both).
• These classes inherit from istream and ostream, which in turn inherit from ios.

File Types: Text and Binary

• Files are often classified as text or binary.
• Text files store content as a sequence of characters and are read sequentially.
• Binary files store content in a binary format (directly mapped to memory).

Opening and Closing Files

• To open a file, link the file to a stream using the "open" method.
• Input-only streams are ifstream; output-only are ofstream; both are fstream.
• The open method needs parameters like file name, mode, and access.
• Closing the stream disassociates the stream and the file; this action flushes data.

Modes for Opening Files

• Modes like ios::app, ios::ate, ios::binary, ios::in, ios::nocreat, ios::noreplace, ios::out, ios::trunc control opening behavior.
• They determine how the file is opened (append, move to end, binary mode, input, etc.)

Checking State Flags

• Member functions like bad(), fail(), eof(), and good() examine stream states (errors, end-of-file).
• Use them to check success of operations.

Stream Pointers

• I/O streams have internal pointers (get pointer and put pointer).
• The get pointer tracks the next element to read.
• The put pointer tracks where the next element will be written.

tellg() and tellp()

• These functions return the current position of the get pointer or the put pointer.

seekg() and seekp()

• You can manipulate the positions of get and put pointers within the stream using seekg() and seekp().

get(), put(), read(), write()

• These methods are used for byte-oriented operations (reading/writing bytes).