Lesson 47: File I/O Part 1: Streams and File Modes

File Input/Output (I/O) allows programs to read data from or write data to permanent storage (files). All C file handling functions are defined in <stdio.h>.

File Streams

C handles file operations using the concept of a stream. A stream is a sequence of bytes.

Standard Streams: Automatically opened when the program starts:
- stdin (Standard Input: Keyboard)
- stdout (Standard Output: Console)
- stderr (Standard Error: Console for error messages)
File Stream: To work with a file, we use the FILE structure, which holds information about the file (location, buffer, position).

c FILE *file_ptr; // A pointer to a FILE structure

File Opening Modes

When opening a file, you must specify the purpose (mode):

Mode	Description	Action if file exists	Action if file doesn't exist
`r`	Read mode	Opens for reading	Returns `NULL` (Error)
`w`	Write mode	Destroys content (truncates)	Creates new file
`a`	Append mode	Writes to end of file	Creates new file
`r+`	Read/Update	Opens for reading and writing	Returns `NULL`
`w+`	Write/Update	Destroys content, opens R/W	Creates new file, opens R/W
`a+`	Append/Update	Opens R/W, write operations append	Creates new file, opens R/W