File Input/Output || chapter 12

File Input/Output (I/O) in C is used to read and write data from and to files. File I/O is an important aspect of programming as it allows programs to store data persistently on disk.

Data Organization:

Data is stored on disk in the form of files, which are organized into directories. Files can be of two types: text files and binary files.

File Operations:

File operations include opening, reading, writing, and closing files.

Opening a File:

The fopen() function is used to open a file in C. It takes two arguments: the name of the file and the mode in which the file should be opened.

c
FILE *fp; 
fp = fopen("file.txt", "r");

Reading from a File:

The fscanf() function is used to read data from a file. It takes two arguments: the file pointer and a format specifier.

c
int x; 
fscanf(fp, "%d", &x);

Trouble in Opening a File:

Opening a file can sometimes fail, and it's important to handle these errors. The fopen() function returns NULL if it fails to open the file.

c
FILE *fp; 
fp = fopen("file.txt", "r"); 
if (fp == NULL) { 
    printf("Failed to open file\n");
 }

Closing the File:

The fclose() function is used to close a file in C.

c
fclose(fp);

Counting Characters, Tabs, Spaces, …:

File I/O can be used to count characters, tabs, spaces, and other elements in a file.

A File-copy Program:

A file-copy program is a simple program that reads data from one file and writes it to another.

Writing to a File:

The fprintf() function is used to write data to a file. It takes two arguments: the file pointer and a format specifier.

c
fprintf(fp, "The value of x is %d\n", x);

File Opening Modes:

There are different modes in which a file can be opened in C. The most commonly used modes are "r" (read), "w" (write), and "a" (append).

String (line) I/O in Files:

File I/O can be used to read and write strings (lines) in files using the fgets() and fputs() functions.

The Awkward Newline:

The newline character can sometimes cause issues when reading and writing strings in files.

Record I/O in Files:

File I/O can be used to read and write data in a structured manner using records.

Text Files and Binary Files:

Files can be of two types: text files and binary files. Text files store data as ASCII characters, while binary files store data in a binary format.

Record I/O Revisited:

Record I/O can be done in text files as well as binary files.

Database Management:

File I/O can be used for simple database management.

Low Level Disk I/O:

Low-level disk I/O functions allow programs to read and write data directly to the disk.

A Low Level File-copy Program:

A low-level file-copy program reads and writes data directly to the disk.

I/O Under Windows:

File I/O under Windows is done using different functions than on Unix-based systems.

Summary:

File Input/Output in C is used to read and write data from and to files. File operations include opening, reading, writing, and closing files. The fopen() function is used to open a file, and the fscanf() function is used to read data from a file. Opening a file can sometimes fail, and it's important to handle these errors. The fclose() function is used to close a file. Different modes can be used to open a file.