convert astronomically large numbers into human readable form in C/C++

Question

My program prints out HUGE numbers - like 100363443, up to a trillion -- and it sort of hard to read them, so I would like to print any number in easy to read form.

right now I use

printf ("%10ld", number);

format

I would appreciate a resulting number using printf. Most of my code is c++ yet I don't want to introduce std::cout, as I already have printf

thanks

Answer 1

Use the non-standard apostrophe flag in the printf format string, if you have that option available and don't mind losing a little bit of portability.

According to my documentation, the ' flag is available for POSIX systems since 1997.

If you are on Unix, Linux, Mac, ... you should have no problem
If you are on Windows, DOS, iSeries, Android, ... all bets are off (but maybe you can install a POSIX layer to your system).

#include <locale.h>
#include <stdio.h>

int main(void) {
  long int x = 130006714000000;

  setlocale(LC_NUMERIC, "en_US.utf-8"); /* important */
  while (x > 0) {
    printf("# %%'22ld: %'22ld\n", x); /* apostrophe flag */
    x *= 2; /* on my machine, the Undefined Behaviour for overflow
            // makes the number become negative with no ill effects */
  }
  return 0;
}

On my system this program produces:

# %'22ld:    130,006,714,000,000
# %'22ld:    260,013,428,000,000
# %'22ld:    520,026,856,000,000
# %'22ld:  1,040,053,712,000,000
# %'22ld:  2,080,107,424,000,000
# %'22ld:  4,160,214,848,000,000
# %'22ld:  8,320,429,696,000,000
# %'22ld: 16,640,859,392,000,000
# %'22ld: 33,281,718,784,000,000
# %'22ld: 66,563,437,568,000,000
# %'22ld: 133,126,875,136,000,000
# %'22ld: 266,253,750,272,000,000
# %'22ld: 532,507,500,544,000,000
# %'22ld: 1,065,015,001,088,000,000
# %'22ld: 2,130,030,002,176,000,000
# %'22ld: 4,260,060,004,352,000,000
# %'22ld: 8,520,120,008,704,000,000