#include <iostream>
#include <sys/types.h>
#include <fcntl.h>

using namespace std;

string Bin(mode_t);

int main() {
    cout << "An int is " << sizeof(int) << " bytes."  << endl;
    cout << "A mode_t is " << sizeof(mode_t) << " bytes."  << endl;


    cout << "S_ISUID = " << Bin(S_ISUID) << endl;
    cout << "S_ISGID = " << Bin(S_ISGID) << endl;
    cout << "S_ISVTX = " << Bin(S_ISVTX) << endl;
    cout << "S_IRUSR = " << Bin(S_IRUSR) << endl;
    cout << "S_IWUSR = " << Bin(S_IWUSR) << endl;
    cout << "S_IXUSR = " << Bin(S_IXUSR) << endl;
    cout << "S_IRGRP = " << Bin(S_IRGRP) << endl;
    cout << "S_IWGRP = " << Bin(S_IWGRP) << endl;
    cout << "S_IXGRP = " << Bin(S_IXGRP) << endl;
    cout << "S_IROTH = " << Bin(S_IROTH) << endl;
    cout << "S_IWOTH = " << Bin(S_IWOTH) << endl;
    cout << "S_IXOTH = " << Bin(S_IXOTH) << endl;
    mode_t flags = S_IRUSR | S_IWUSR | S_IXUSR | S_IRGRP | S_IROTH;
    cout << "S_IRUSR | S_IWUSR | S_IXUSR | S_IRGRP | S_IROTH = "
         << Bin(flags) << endl;;

    return 0;
}

string Bin(mode_t flag){
    string rv;
    int k = 0;
    // we only use the lower 4 hex digits
    for(int i = 0; i < 12;  ++i) {
      if (k == 3) {
         rv = ' ' + rv;
         k = 0;
      }
      k++;
      rv = static_cast<char>(flag%2+'0') + rv;
      flag /= 2;
    }
    return rv;
}