File Handling in C Programming

• File handling in C involves creating, opening, reading, writing, and closing files.
• Functions like fopen(), fwrite(), fread(), fseek(), and fprintf() are used for file input/output.
• C program operations are typically done on a prompt/terminal, and the output is not automatically stored.
• File handling is utilized in real-world applications.
• Operations on files can include creation, opening, reading, writing, and deleting.

Types of Files in C

• Files are classified based on data storage: text files and binary files.

Text files

• Text files store data as ASCII characters, forming a stream of characters.
• Each line ends with a newline character (\n).
• Text files can be read or edited using any text editor.
• Text files typically use the .txt extension for file storage.
• Text files can also store source code.

Binary files

• Binary files contain data in binary format (0s and 1s).
• Binary files store data in a manner similar to main memory.
• Binary files can only be created and read within a program.
• Binary files offer enhanced security due to their readability.
• Binary files generally use the .bin file extension.

File Handling Functions

• C library offers functions to open, read, write, search, and close files.
• fopen(): Opens a new or existing file.
• fprintf(): Writes data into the file.
• fscanf(): Reads data from the file.
• fputc(): Writes a character into the file.
• fgetc(): Reads a character from the file.
• fclose(): Closes the file.
• fseek(): Sets the file pointer to a specified position.
• fputw(): Writes an integer to a file.
• fgetw(): Reads an integer from a file.
• ftell(): Returns the current position.
• rewind(): Sets the file pointer to the beginning of the file.

Opening Files : fopen()

• Files must be opened before reading, writing, or updating.
• Syntax: fp = fopen(const char filename, const char mode);
• fopen() accepts these parameters:
  • filename: The name of the file (string), includes the path if not in the current directory.
  • mode: The mode in which the file is to be opened (string).
• Return Value:
  • Returns a file pointer upon successful opening.
  • Returns NULL if the file cannot be opened.

File Opening Modes

• File opening modes specify the permitted operations.
• Modes are passed as arguments to the fopen() function.
• r: Searches the file, loads into memory, sets up a pointer to the first Character or returns NULL if the file doesn't exist.
• w: Opens for writing in text mode. It overwrites if the file exists, or creates a new file if it doesn't. Returns NULL if fails
• a: Searches the file, loads into memory, and sets a pointer to the last character to append. If the file doesn't exist, a new file is created.
• r+: Opens for both read and write modes and sets up a pointer to the first character, or returns NULL if fails.
• w+: Opens for both read and write modes. It overwrites if the file exists, or creates a new file if it doesn't. Returns NULL if fails.
• a+: Opens for both reading and appending modes. If the file doesn't exist, a new file is created. Returns NULL if fails.
• To perform operations on a binary file, append 'b' to the mode (e.g., "wb" or "a+b").
• The fopen function:
  • Searches for the specified file
  • Loads it from the disk into a buffer for efficient read operations.
  • Establishes a character pointer that points to the first character in the file.

Creating a File

• The fopen() function creates a file if it does not exist, contingent on the mode that allows file creation i.e. w, w+, a, a+ etc.
• The w mode is used to write in a file.

Writing to a File using fprintf()

• The fprintf() function writes a set of characters into a file.
• It sends formatted output to a stream.
• If a specified file already exists, the old content will be deleted and replaced with the new information.

Appending Content

• The a mode is used to add content to a file without deleting the existing data.

Reading From a file

• The r mode is used to read a file.
• The fgets() function is used to read the content from a file.
• Parameters of the fgets() function:
  • Specifies where to store the file content
  • Designates the max size of data to read
  • requires a file pointer being used to read the file
• The fgets function only reads the first line of the file.
• The while loop function is used to read every line of the file.
• If a file doesn't exist and is opened for reading, the fopen() function will return NULL.
• A check for NULL with an if statement confirms file existence.

Reading Files : fscanf()

• fscanf() reads a set of characters from a file, word by word, and returns EOF at the end.

putc() function

• The function writes a character to a specified stream.
• It is a standard library function defined in the <stdio.h> header file.
• Converts character to unsigned char and writes to stream, increments file pointer.
• Syntax: int putc(int ch, FILE *fptr);
  • ch: The character to write.
  • fptr: Pointer to a FILE object.

getc() function

• It is a C library function that reads a character from a file that has been opened in read mode by the fopen() function.
• Syntax: int getc( FILE * fptr );

putw() and getw() functions

• The putw() function writes an integer to a file - Syntax: putw (int num, FILE *fptr);
• The getw() function reads an integer from a file opened in read mode - Syntax: int getw( FILE * fptr);