原文连接

Objective-C版

// 随机生成字符串(由大小写字母、数字组成)
+ (NSString *)random: (int)len {
    char ch[len];
    for (int index=0; index<len; index++) {
        int num = arc4random_uniform(75)+48;
        if (num>57 && num<65) { num = num%57+48; }
        else if (num>90 && num<97) { num = num%90+65; }
        ch[index] = num;
    return [[NSString alloc] initWithBytes:ch length:len encoding:NSUTF8StringEncoding];
// 随机生成字符串(由大小写字母组成)
+ (NSString *)randomNoNumber: (int)len {
    char ch[len];
    for (int index=0; index<len; index++) {
        int num = arc4random_uniform(58)+65;
        if (num>90 && num<97) { num = num%90+65; }
        ch[index] = num;
    return [[NSString alloc] initWithBytes:ch length:len encoding:NSUTF8StringEncoding];
Swift版
extension String {
    /// 生成随机字符串
    /// - Parameters:
    ///   - count: 生成字符串长度
    ///   - isLetter: false=大小写字母和数字组成，true=大小写字母组成，默认为false
    /// - Returns: String
    static func random(_ count: Int, _ isLetter: Bool = false) -> String {
        var ch: [CChar] = Array(repeating: 0, count: count)
        for index in 0..<count {
            var num = isLetter ? arc4random_uniform(58)+65:arc4random_uniform(75)+48
            if num>57 && num<65 && isLetter==false { num = num%57+48 }
            else if num>90 && num<97 { num = num%90+65 }
            ch[index] = CChar(num)
        return String(cString: ch)
/// 大小写字母和数字组成