C File I/O (Input/Output)

File I/O (Input/Output) in C refers to the process of reading from and writing to files on the disk. File I/O in C is done using the standard library functions provided in stdio.h. These functions allow you to open files, read from or write to them, and close them when done.

Types of File I/O operations

1. Opening a file

2. Reading from a file

3. Writing to a file

4. Closing a file

Open a File

To open a file in C, you use the fopen() function. It requires two arguments:

1. The name of the file.

2. The mode in which you want to open the file.

Syntax:


FILE *fopen(const char *filename, const char *mode);

Explanation:

  1. filename is the name of the file to be opened.
  2. mode specifies the file access mode (whether to read, write, append, etc.).

There are many modes of File

Mode
Description
r
Read mode: Open an existing file for reading
w
Write mode: Create an empty file for writing. If the file already exists, it’s truncated.
a
Append mode: Open an existing file for appending or create a new file if it doesn’t exist.
r+
Read and write mode: Open for both reading and writing. The file must exist.
w+
Write and read mode: Create an empty file for both writing and reading.
a+
Append and read mode: Open a file for reading and appending.
b
Binary mode: Add this character to modes to work with binary files (e.g., “rb”, “wb”, etc.).

C File I/O (Input/Output) – Interview Questions

Q 1: What is File I/O in C?

Ans: Reading and writing data to files.

Q 2: Which header file is used for file handling?

Ans: <stdio.h>.

Q 3: What is FILE?

Ans: A structure that holds file information.

Q 4: What function is used to open a file?

Ans: fopen().

Q 5: What are file modes in C?

Ans: r, w, a, r+, w+, a+.

C File I/O (Input/Output) – Objective Questions (MCQs)

Q1. Which header file is required for file handling functions in C?





Q2. What is the data type of a file pointer in C?





Q3. Which function is used to open a file in C?





Q4. What will fclose() do in C?





Q5. Which of the following is a valid file opening mode in C?





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