C Program that prints the source code of a C file with the same name

Question

So I need to write a code with this compilation flags:

gcc -ansi -pedantic -Wall

All on Linux based OS. The output program should print its own source code. If I change the output file name AND there is a C file with the same name in the folder it would print its content.

Up until now I managed to pull this:

#include <stdio.h>
int main()
{
    char c; 
    FILE *my_file = fopen(__FILE__, "r");
    while (c != EOF)
    {
        c = fgetc(my_file);
        putchar(c);
    }
    fclose(my_file);
    return 0;
}

But if I change the file name and the C file name it gives me an error. Example: For files: prnt.c, prnt

Consule -> os/23$ ./prnt
#include <stdio.h>
int main()
{
    char c; 
    FILE *my_file = fopen(__FILE__, "r");
    while (c != EOF)
    {
        c = fgetc(my_file);
        putchar(c);
    }
    fclose(my_file);
    return 0;
}

for same file after I change the name to test.c, test (with out compilation)

/os/23$ ./test 
Segmentation fault (core dumped)

It is happening because of the __ FILE __ macro, it changes after compilation to the original file name. The question is how do I solve this problem?

First: int c; ... then check the return value of fopen(): ie if (my_file == NULL) { perror(__FILE__); exit(EXIT_FAILURE); } — pmg
– pmg, Commented Jun 5, 2021 at 10:04
I don't know exactly what you mean by "change the output file name", but I expect you need to look at argv[0] for the name the binary was executed as on the command line. — Paul Hankin
– Paul Hankin, Commented Jun 5, 2021 at 10:10
Hm, the source file would need to be part of the final executable. You might rely on the source residing parallelly to the executable and cut away the path from __FILE__. — Aconcagua
– Aconcagua, Commented Jun 5, 2021 at 10:36
while (c != EOF) is undefined behaviour, by the way, as c is not initialised! You might initialise to ~EOF to make assure it being different from. And it should be of type int to guarantee a byte 0xff really differ from EOF (apparently your char is signed anyway, otherwise you'd end up in an endless loop!). — Aconcagua
– Aconcagua, Commented Jun 5, 2021 at 10:41
You probably misunderstand the assignment. See en.m.wikipedia.org/wiki/Quine_(computing) — n. m. could be an AI
– n. m. could be an AI, Commented Jun 5, 2021 at 15:15

Nikman · Accepted Answer · 2021-06-17 12:52:03Z

1

So I checked into Paul Hankin's suggestion, I managed to solve the problem. Hope that in the future it will help somebody.

My Solution:

#include <stdio.h>
#include <string.h>
int main(int argc, char* argv[])
{
    /*
    This program prints the source code
    of the 'C' file with the same name in the
    same directory.
    */
    char c = 'a'; /* Initialization before while loop.*/
    char* locat = argv[0]; /* The path to the program file.*/
    char suff[3] = ".c\0";
    FILE* my_file;

    strcat(locat, suff); /* Doesn't work for Windows.*/

    my_file = fopen(locat, "r");
    while (c != EOF)
    {
        c = fgetc(my_file);
        putchar(c);
    }
    fclose(my_file);
    return 0;
}

answered Jun 17, 2021 at 12:52

Nikman

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