ios CCRandomGenerateBytes generates fixed-length random string

Sometimes we need to generate a random string will meet the needs of the project, which is now described a method (using Apple's own library);

First, import the header files in the project

//这是导入了所有加密库的头文件
#import <CommonCrypto/CommonCrypto.h>
//如果只是使用random函数，那么只要做如下导入即可
#import <CommonCrypto/CommonRandom.h>

Second, the use of function

//利用CCRandomGenerateBytes实现随机字符串的生成
- (NSString *)randomString:(NSInteger)length {
    length = length/2;
    unsigned char digest[length];
    CCRNGStatus status = CCRandomGenerateBytes(digest, length);
    NSString *s = nil;
    if (status == kCCSuccess) {
        s = [self stringFrom:digest length:length];
    } else {
        s = self;
    }
    NSLog(@"randomLength---:%@",s);
    return s;
}
//将bytes转为字符串
- (NSString *)stringFrom:(unsigned char *)digest length:(NSInteger)leng {
    NSMutableString *string = [NSMutableString string];
    for (int i = 0; i < leng; i++) {
        [string appendFormat:@"%02x",digest[i]];
    }
    NSLog(@"final stringFrom:%@",string);
    return string;
}