Computer Science – 10.3 Files | e-Consult
10.3 Files (1 questions)
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Computer programs access and manipulate files through a series of operations involving file pointers, file descriptors, and I/O operations. Here's a breakdown of these concepts:
- File Pointers: A file pointer is a variable that stores the current position within a file. It indicates where the next read or write operation should occur. The file system maintains the file pointer's location. When a read or write operation is performed, the file pointer is updated to reflect the new position.
- File Descriptors: A file descriptor is a non-negative integer that represents an open file. When a program opens a file, the operating system assigns it a unique file descriptor. This descriptor is used by the program to refer to the file. File descriptors are used by system calls to identify which file the operation should be performed on.
- Input/Output (I/O) Operations: I/O operations are the fundamental operations used to read data from and write data to files. Common I/O operations include:
- Opening a file: This establishes a connection between the program and the file, allocating a file descriptor.
- Reading from a file: This retrieves data from the file, moving the file pointer forward.
- Writing to a file: This stores data in the file, moving the file pointer forward.
- Closing a file: This releases the file descriptor, indicating that the program is finished with the file. It's crucial to close files to ensure data is properly written and resources are released.
Process Overview:
- The program requests to open a file from the operating system. The OS allocates a file descriptor and updates the file pointer.
- The program uses I/O operations (read, write) to interact with the file. Each operation updates the file pointer.
- When the program is finished, it closes the file. This releases the file descriptor and ensures that any buffered data is written to the disk.
Example: Consider a program that reads a text file. The program first opens the file, obtaining a file descriptor. It then uses a read operation to read data from the file, which advances the file pointer. The program continues reading until it reaches the end of the file. Finally, it closes the file, releasing the file descriptor.