Different format of __DATE__ macro

Question

C has a predefined macro __DATE__, that shows the date of the compiled source file .
The date is displayed in the format "Mmm dd yyyy" .

Is there any way to be formatted this date, using macros ?
In this format "yyyy Mmm dd".

Instead of being :

Jul 19 2013

Should be :

2013 Jul 19

Answer 1

In C you could have a macro that generates a compound literal on the fly that has the order that you like, something like

#define FDATE (char const[]){ __DATE__[7], __DATE__[8], ..., ' ', ... , '\0' }

in all places where it matters your optimizer should be able to handle this efficiently.

Answer 2

In case anyone is looking for a way to convert Mmm DD YYYY into a string YYMMDD with ASCII digits only (like "220103"), then here's the code for that. It should work in C and C++ both:

#include <stdio.h>

const char version[6+1] =
{
   // YY year
   __DATE__[9], __DATE__[10],

   // First month letter, Oct Nov Dec = '1' otherwise '0'
   (__DATE__[0] == 'O' || __DATE__[0] == 'N' || __DATE__[0] == 'D') ? '1' : '0',
   
   // Second month letter
   (__DATE__[0] == 'J') ? ( (__DATE__[1] == 'a') ? '1' :       // Jan, Jun or Jul
                            ((__DATE__[2] == 'n') ? '6' : '7') ) :
   (__DATE__[0] == 'F') ? '2' :                                // Feb 
   (__DATE__[0] == 'M') ? (__DATE__[2] == 'r') ? '3' : '5' :   // Mar or May
   (__DATE__[0] == 'A') ? (__DATE__[1] == 'p') ? '4' : '8' :   // Apr or Aug
   (__DATE__[0] == 'S') ? '9' :                                // Sep
   (__DATE__[0] == 'O') ? '0' :                                // Oct
   (__DATE__[0] == 'N') ? '1' :                                // Nov
   (__DATE__[0] == 'D') ? '2' :                                // Dec
   0,

   // First day letter, replace space with digit
   __DATE__[4]==' ' ? '0' : __DATE__[4],

   // Second day letter
   __DATE__[5],

  '\0'
};

int main(void)
{
  puts(__DATE__);
  puts(version);
}

Output:

Jan  3 2022
220103

Disassembly (gcc x86_64):

version:
        .string "220103"