3. File Handling

File Handling in C

A file is a basic structure used to permanently store data outside an application's RAM limits on a physical hard drive.

Types of Files

• Text Files (.txt): Store character output logically mapped and readable by text editors.
• Binary Files (.bin): Store data structurally in 1s and 0s, evaluating more efficiently and securely.

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Core Operations Matrix

To effectively manage files locally, C utilizes an internal FILE pointer.

Mode	Operation	Core Behavior
r	Read	Opens a file for reading. If it does not exist, fopen() returns NULL.
w	Write	Writes entirely to a file. Overwrites existing content.
a	Append	Adds outputs exclusively to the end of the file.
rb / wb	Read/Write	Reads and writes logically in binary mode.

The FILE Pointer

Every file operation fundamentally relies on the FILE pointer:

FILE *fptr; 
fptr = fopen("my_document.txt", "w");

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Practical Functions

1. fopen(): Opens a document explicitly based on mode.
2. fclose(): Safely closes a file to prevent memory leaks and file corruption.
3. fputc() / fgetc(): Character-based read/write.
4. fprintf() / fscanf(): Formatted I/O operations functionally similar to standard printf/scanf.
5. fgets() / fputs(): Safely read/write string lines explicitly.

Traversal Operations

• fseek(fptr, offset, SEEK_SET/SEEK_CUR/SEEK_END): Moves the pointer inside the file logically.
• ftell(fptr): Retreives the current file pointer byte offset.