How do you create a random 64 bit number? [closed]

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Closed 6 years ago.

I have part of a spec that requires me to create a random 64 bit number with the following converted to a character string : (0 to 2^63 - 1)

I have no idea what this means in the brackets, can anyone help?

回答1:

The parenthesis is set-builder notation for a random 64 bit number between 0 and 2^63-1, not including 0 nor 2^63-1.

回答2:

Since you didn't specify a programming language I'll give a solution in C and then you can adapt it to whatever programming language you might be using if it turns out not to be C (or a close relative).

You can just call arc4random twice and concatenate the values:

 #include <stdint.h>
 #include <stdlib.h>

 int64_t rand64(void)
 {
     uint64_t r_lo = (uint64_t)arc4random();
     uint64_t r_hi = (uint64_t)arc4random();
     return (int64_t)((r_hi << 31) | (r_low >> 1));
 }

You can convert this to a hex ASCII string quite easily:

 char s[17];

 int64_t r = rand64();
 sprintf(s, "%16llx", r);

(If you need it as decimal or some other format then just modify the sprintf format string accordingly).

来源：https://stackoverflow.com/questions/17656312/how-do-you-create-a-random-64-bit-number