Tutorials

C Library – stdio.h

Posted in C Tutorial

Updated on Oct 06, 2024

By Mari Selvan

👁️ 615 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

The <stdio.h> header file in C is one of the most commonly used and essential libraries. It provides functionalities for input and output operations, making it a crucial part of any C programmer's toolkit.

This guide will give you an in-depth look at what <stdio.h> offers, its key functions, and how to use them effectively.

🎯 Purpose of <stdio.h>

<stdio.h> stands for Standard Input Output Header. It contains definitions of macros, constants, and declarations of functions and types used for performing input and output operations in C.

🔑 Key Features

Standard I/O Functions: Provides functions for reading and writing data.
File Handling: Supports file operations such as opening, reading, writing, and closing files.
Buffer Management: Includes functions for managing input and output buffers.

🔍 Common Functions

Here are some of the most commonly used functions provided by <stdio.h>:

printf: Prints formatted output to the standard output (usually the screen).
scanf: Reads formatted input from the standard input (usually the keyboard).
fopen: Opens a file and returns a file pointer.
fclose: Closes an opened file.
fread: Reads data from a file.
fwrite: Writes data to a file.
fgets: Reads a string from a file.
fputs: Writes a string to a file.
fscanf: Reads formatted input from a file.
fprintf: Prints formatted output to a file.

📝 Example Usage

printf and scanf

These functions are used for standard input and output operations.

example.c

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#include <stdio.h>

int main() {
  int num;
  printf("Enter an integer: ");
  scanf("%d", &num);
  printf("You entered: %d\n", num);
  return 0;
}

💻 Output

Output

Enter an integer: 36
You entered: 36

File Operations

The <stdio.h> library provides robust functions for file handling, allowing you to read from and write to files.

Example: Reading from a File

example.c

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#include <stdio.h>

int main() {
  FILE *file;
  char buffer[100];

  file = fopen("example.txt", "r");
  if (file == NULL) {
    perror("Error opening file");
    return -1;
  }

  while (fgets(buffer, 100, file) != NULL) {
    printf("%s", buffer);
  }

  fclose(file);
  return 0;
}

Example: Writing to a File

example.c

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#include <stdio.h>

int main() {
  FILE *file;
  file = fopen("example.txt", "w");
  if (file == NULL) {
    perror("Error opening file");
    return -1;
  }

  fprintf(file, "Hello, World!\n");
  fclose(file);
  return 0;
}

Buffer Management

The <stdio.h> library also includes functions for managing input and output buffers, which can optimize performance by reducing the number of I/O operations.

Example: Flushing the Output Buffer

example.c

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#include <stdio.h>

int main() {
  printf("This will be printed immediately.\n");
  fflush(stdout); // Flush the output buffer
  return 0;
}

Constants and Macros

<stdio.h> defines several constants and macros that are useful for file operations and error handling:

EOF: Indicates the end of a file.
NULL: Represents a null pointer.
FOPEN_MAX: Maximum number of files that can be opened simultaneously.
FILENAME_MAX: Maximum length of a filename.

Error Handling

When performing I/O operations, it’s crucial to handle errors gracefully. The <stdio.h> library provides several functions to assist with this:

perror: Prints a descriptive error message to stderr.
feof: Checks if the end of a file has been reached.
ferror: Checks for errors in a file stream.
clearerr: Clears the error and end-of-file indicators for a file stream.

Example: Handling File Errors

example.c

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#include <stdio.h>

int main() {
  FILE *file;

  file = fopen("nonexistent.txt", "r");
  if (file == NULL) {
    perror("Error opening file");
    return -1;
  }

  // Perform file operations

  fclose(file);
  return 0;
}

🎉 Conclusion

The <stdio.h> header file is a cornerstone of C programming, providing essential functions for input and output operations.

Understanding how to use its functions effectively can greatly enhance your ability to perform file handling, manage I/O buffers, and handle errors in your C programs.