Question

What is the best way to check if a file exists, if not create it and write info by using mac
library <.mach-o/dyld.h> or other..?

Answer 1

Your question is unclear.

Checking if a file exists is trivial – use stat() or access(), e.g.:

#include <unistd.h>

int res = access(path, R_OK);
if (res < 0) {
    if (errno == ENOENT) {
         // file does not exist
    } else if (errno == EACCES) {
         // file exists but is not readable
    } else {
         // uh oh
    }
}

Creating a file is similarly trivially – use open() or fopen(). Find any good book on C programming, this is the most fundamental thing most any book will teach.

But what has <mach-o/dyld.h> got to do with it?