Formatted and Unformatted Input Output in C

Why they are called formatted I/O?

Formatted I/O functions are called "formatted" because they allow you to specify the format of the input or output using format specifiers. Format specifiers are special characters that define how the data should be interpreted or displayed. For example, %d is used for integers, %f for floating-point numbers, %s for strings, etc. This formatting capability provides flexibility & control over how data is read or written.

Unformatted I/O Functions

Unformatted I/O functions in C handle raw data without any formatting. They deal with individual characters or strings as a whole. Some commonly used unformatted I/O functions are:

1. getch()

This function reads a single character from the console without echoing it back to the screen. It doesn't wait for the user to press Enter. For example:

#include <stdio.h>
#include <conio.h>
int main() {
    char ch;
    printf("Press any key: ");
    ch = getch();
    printf("\nYou pressed: %c\n", ch);
    return 0;
}

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Output:

Press any key: (User presses 'A')
You pressed: A

2. getche()

This function is similar to getch(), but it echoes the character back to the screen. For example:

#include <stdio.h>
#include <conio.h>
int main() {
    char ch;
    printf("Press any key: ");
    ch = getche();
    printf("\nYou pressed: %c\n", ch);
    return 0;
}

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Output:

Press any key: A (User presses 'A')
You pressed: A

3. getchar()

This function reads a single character from the console & waits for the user to press Enter. It returns the ASCII value of the character. For example:

#include <stdio.h>
int main() {
    char ch;
    printf("Enter a character: ");
    ch = getchar();
    printf("You entered: %c\n", ch);
    return 0;
}

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Output:

Enter a character: A (User enters 'A' & presses Enter)
You entered: A

4. putchar()

This function writes a single character to the console. It takes a character as an argument & returns the same character if successful. For example:

#include <stdio.h>

int main() {
    char ch = 'A';
    putchar(ch);
    putchar('\n');
    return 0;
}

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Output:

A

5. gets()

This function reads a line of text from the console until a newline character ('\n') is encountered. It stores the input in a character array (string). However, gets() is considered unsafe as it doesn't perform bounds checking & can lead to buffer overflow vulnerabilities. For example:

#include <stdio.h>
int main() {
    char str[100];
    printf("Enter a string: ");
    gets(str);
    printf("You entered: %s\n", str);
    return 0;
}

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Output:

Enter a string: Hello, World!
You entered: Hello, World!

6. puts()

This function writes a string to the console followed by a newline character. It takes a string as an argument & returns a non-negative value if successful. For example:

#include <stdio.h>
int main() {
    char str[] = "Hello, World!";
    puts(str);
    return 0;
}

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Output:

Hello, World!

7. putch()

This function is similar to putchar(), but it is a non-standard function specific to certain compilers like Turbo C. It writes a single character to the console. For example:

#include <stdio.h>
#include <conio.h>
int main() {
    char ch = 'A';
    putch(ch);
    return 0;
}

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Output:

A

Why are they called unformatted I/O?

Unformatted I/O functions are called "unformatted" because they deal with raw data without any formatting. They handle individual characters or strings as a whole without the need for format specifiers. Unformatted I/O functions provide a simple way to read & write characters or strings directly without any formatting overhead.

Formatted I/O Functions vs Unformatted I/O Functions

Frequently Asked Questions 

Can we mix formatted and unformatted I/O functions in a program?

Yes, you can use both formatted and unformatted I/O functions in the same program as per your requirements.

Is it necessary to use format specifiers with formatted I/O functions?

Yes, format specifiers are essential when using formatted I/O functions to specify the type and format of the data.

Are unformatted I/O functions faster than formatted I/O functions?

Generally, unformatted I/O functions are faster because they don't have the overhead of parsing format specifiers.

Conclusion

In this article, we learned about formatted and unformatted I/O functions in C. Formatted I/O functions like printf(), scanf(), sprintf(), and sscanf() provide control over data formatting using format specifiers. Unformatted I/O functions such as getch(), getche(), getchar(), putchar(), gets(), puts(), and putch() handle raw data without formatting. 

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