Questions
I m a Java head mainly, and I want a way to generate a pseudo-random number between 0 and 74. In Java I would use the method:
Random.nextInt(74)
I m not interested in a discussion about seeds or true randomness, just how you accomplish the same task in Objective-C. I ve scoured Google, and there just seems to be lots of different and conflicting bits of information.
Answers
You should use the arc4random_uniform() function. It uses a superior algorithm to rand. You don t even need to set a seed.
#include <stdlib.h>
// ...
// ...
int r = arc4random_uniform(74);
The arc4random man page:
NAME
arc4random, arc4random_stir, arc4random_addrandom -- arc4 random number generator
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
u_int32_t
arc4random(void);
void
arc4random_stir(void);
void
arc4random_addrandom(unsigned char *dat, int datlen);
DESCRIPTION
The arc4random() function uses the key stream generator employed by the arc4 cipher, which uses 8*8 8
bit S-Boxes. The S-Boxes can be in about (2**1700) states. The arc4random() function returns pseudo-
random numbers in the range of 0 to (2**32)-1, and therefore has twice the range of rand(3) and
random(3).
The arc4random_stir() function reads data from /dev/urandom and uses it to permute the S-Boxes via
arc4random_addrandom().
There is no need to call arc4random_stir() before using arc4random(), since arc4random() automatically
initializes itself.
EXAMPLES
The following produces a drop-in replacement for the traditional rand() and random() functions using
arc4random():
#define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1))
Source
License : cc by-sa 3.0
http://stackoverflow.com/questions/160890/generating-random-numbers-in-objective-c
Related