Strange behavior when attempting to obtain number of digits of unsigned long long´s maximum

Question

I like the luxury. I wanted to invent a way for you to obtain the number of digits the unsigned long long int maximum possess. All that automatically. Here it is:

#include <limits.h>
#include <string.h>

#define STRINGIFY(x) #x
#define ULLONG_MAX_STRING STRINGIFY(ULLONG_MAX)
#define NUMERAL_MAXIMUM strlen(ULLONG_MAX_STRING)

Does this work as described?

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Now about the strange behavior that pretty much answers the question from above. If I declare a variable like so (-std=c99 specific):

char variable [NUMERAL_MAXIMUM];

instead of declaring automatic-scoped variable, array with the size of 20, it terminates the program before it even reaches that line. Though if I don´t declare the variable like so, nothing terminates and the program continues to work.

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What is going on?

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Update: Even more strange is that the program does that only if I use this obtained length as a size of an array.

Answer 1

IIUC, the OQ wants the size needed to print the maximum values in decimal. The below works for sizes of 8 bits upto 64 bits, at least for CHAR_BIT==8 :

#include <stdio.h>
#include <limits.h>

#define ASCII_SIZE(s) ((3+(s) * CHAR_BIT) *4 / 13)

int main(void)
{
printf("unsigned char : %zu\n", ASCII_SIZE(sizeof(unsigned char)) );
printf("unsigned short int : %zu\n", ASCII_SIZE(sizeof(unsigned short int)) );
printf("unsigned int : %zu\n", ASCII_SIZE(sizeof(unsigned int)) );
printf("unsigned long : %zu\n", ASCII_SIZE(sizeof(unsigned long)) );
printf("unsigned long long : %zu\n", ASCII_SIZE(sizeof(unsigned long long)) );

printf("          Ding : %u\n", UINT_MAX );
printf("     Lang Ding : %lu\n", ULONG_MAX );
printf("Heel lang Ding : %llu\n", ULLONG_MAX );

return 0;
}

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Output:

unsigned char : 3
unsigned short int : 5
unsigned int : 10
unsigned long : 20
unsigned long long : 20
          Ding : 4294967295
     Lang Ding : 18446744073709551615
Heel lang Ding : 18446744073709551615