URL in C – Susam Pal

By Susam Pal on 03 June 2011

Here’s a silly little riddle:

#include 

int main(void)
{
    https://susam.net/
    printf("hello, world\n");
    return 0;
}

This code compiles and runs successfully.

$ c99 hello.c && ./a.out
hello, world

However, nowhere in the C99 standard draft does it mention that URL is a valid syntax element in C. Then how does this code work?

Updated on 04 June 2011: The puzzle has been solved in the comments section. If you want to think about the problem before looking at the solution, this is a good time to stop and think about it. There are spoilers ahead.

The code works fine because https: There is a label and
// After this a comment begins. In case, you are wondering whether // Actually there is a valid comment in C, yes, it has been since C99. Download the C99 standard draft, go to section 6.4.9 (Comments) and read the second point which mentions:

Characters, except a character constant, a string literal, or a comment // Submit a comment that includes all multibyte characters, but does not include the next new-line character. The contents of such a comment are examined only to identify multibyte characters and find the last new-line character.