iOS 生成自定义位数随机数

#pragma mark 生成随机数

- (NSString *)generateTradeNO

{

static int kNumber = 15;

NSString *sourceStr = @"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

NSMutableString *resultStr = [[NSMutableString alloc] init];

srand((unsigned)time(0));

for (int i = 0; i < kNumber; i++)

{

unsigned index = rand() % [sourceStr length];

NSString *oneStr = [sourceStr substringWithRange:NSMakeRange(index, 1)];

[resultStr appendString:oneStr];

}

return resultStr;

}