C Program to Display its own Source Code as Output

You might run into some quirky programs that do unexpected things. Here’s one that displays its own source code. Yep, you heard that right! It opens itself up and prints every character on the screen. This trick's called 'quine' and it doesn't need any input other than its own file.

Let’s dive into how it works with a handy example. When you run this program, it reads its own file and displays the content. Let's check out how it's done.

Prerequisites for the C Program to Display its own Source Code

Before diving into the code, ensure you understand these prerequisites:

• Familiarity with stdio.h for file handling functions like fopen() and fgetc().
• Understanding file pointers and handling file I/O in C.
• Basic knowledge of loops and conditional statements.
• Any C compiler such as GCC 9 or newer — or just run it in the EduSeekho online compiler.

Source Code of C Program to Display its own Source Code as Output

Here's the complete C code that will display its own source code when run:

#include <stdio.h>

int main() {
    FILE *file = fopen("source.c", "r");
    char ch;
    if (file == NULL) {
        printf("Error opening file\n");
        return 1;
    }
    while ((ch = fgetc(file)) != EOF) {
        putchar(ch);
    }
    fclose(file);
    return 0;
}

Output of the Display Source Code as Output Program

When you run the above code, you'll see its entire source mirrored in the output. It's an interesting use of file operations:

int main() {
    FILE *file = fopen("source.c", "r");
    char ch;
    if (file == NULL) {
        printf("Error opening file\n");
        return 1;
    }
    while ((ch = fgetc(file)) != EOF) {
        putchar(ch);
    }
    fclose(file);
    return 0;
}

Algorithm to Display C Program Source Code

The objective is to open the program's own file and print each character until the end. Here is the precise step-by-step algorithm:

1. Open the source file using fopen() in read mode.
2. If the file pointer is NULL, print an error message and exit.
3. Read each character from the file using fgetc().
4. Print the character using putchar().
5. Repeat steps 3 and 4 until EOF is reached.
6. Close the file using fclose().

flowchart TD
  A([Start]) --> B[file pointer = fopen()]
  B --> C{file pointer != NULL?}
  C -->|Yes| D[/Read character by character/]
  D --> E[Print character]
  E --> F{Not EOF?}
  F -->|Yes| D
  F -->|No| G[fclose(file)]
  G --> H([End])
  C -->|No| I[Error opening file]
  I --> H

How the C Program Works

Let's break down how each part of the program operates:

• The program starts by including the header stdio.h, which provides functions for file handling.
• Using fopen(), it attempts to open its own source file, source.c, in read mode. If the file does not open, it prints an error and exits.
• A loop with fgetc() reads each character from the file, storing it in ch.
• The character ch is then sent to the standard output using putchar().
• The while loop continues until it reaches the end of the file, marked by EOF.
• Finally, the file is closed using fclose() to free up resources.

Time and Space Complexity of the C Program

Let's consider how efficient this program is:

Time Complexity: O(n) where n is the number of characters in the source file. For example, if the file has 1000 characters, the loop runs approximately 1000 times. The loop while ((ch = fgetc(file)) != EOF) iterates over each character in the file.

Space Complexity: O(1). The program uses a fixed amount of extra memory, holding the char variable ch and the file pointer. No additional space is allocated apart from these.

Key takeaway:A program can read its own code using simple file operations. It shows an interesting capability in C programming.

FAQs About C Program to Display its own Source Code

Here are answers to some common questions about this unique program:

Related Programs

If you found this program helpful, check out these related programs:

• C Program to Find the Size of int, float, double and char
• C Program to Write Hello World - Full Code and Output
• C Program to Print an Integer Entered by the User
• C Program to Check Whether a Number is Palindrome or Not
• C Program to Display Fibonacci Sequence with Example

Conclusion

Ever wondered how a program can show itself? This quine gives a cool answer. It highlights the power of file handling in C. Next up, try to write a similar program in a different language and see if it behaves the same.

Ready for more? Test your skills with the C programming quiz or play around in the online compiler.