Best way to generate NSData object with random bytes of a specific length?

Question

If I create a new NSData object of a specific size using dataWithBytes:length:, what is the most efficient way to create the input bytes (20 Mb worth) of random characters, pref

Answer 1

urandom is more efficient.

Here is a category to generate random buffers:

@interface NSMutableData(Random)
+(id)randomDataWithLength:(NSUInteger)length;
@end

@implementation NSMutableData(Random)
+(id)randomDataWithLength:(NSUInteger)length
{
    NSMutableData* data=[NSMutableData dataWithLength:length];
    [[NSInputStream inputStreamWithFileAtPath:@"/dev/urandom"] read:(uint8_t*)[data mutableBytes] maxLength:length];
    return data;
}
@end