I first tried to use some preprocessor directives, like they did in hxpCTF```#define _str(x) #x#define str(x) _str(x)#define batpwn str(const char* flag =#include './flag.txt')```
This however didn't compile, with error about the open parenthesis.So I changed directions and tried to find a different way to include a file while compilation, after looking at some other writeups for simillar challenges I saw this cool thing you can do with inline assembly `.incbin`
Solution:```int main(void) {    __asm__ (        ".incbin \"./flag.txt\""    );    return 0;}``` Let the service compile this code, then use `strings` on it to find the flag included.Flag: `batpwn{CTFs_the_only_way_towards_actual_hacking}`