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