How to generate 18-bit non-repeating characters in php

In web development, it is often necessary to generate some non-repeating random characters, such as order numbers, verification codes, etc. PHP is a widely used development language, and we can easily use PHP to implement this function. This article will introduce how to generate 18-bit non-repeating characters in PHP, as well as the corresponding algorithms and techniques.

1. Use random numbers to generate non-repeating characters

In PHP, we can use the rand() function or mt_rand() function to generate random numbers. However, the random numbers generated by this method are likely to repeat, so some skills are needed to ensure that the generated characters do not repeat.

The following is a simple method:

1. Define an empty string $chars to store the generated characters;

2. Generate a random character each time After that, use the strpos() function to find whether the character already exists in $chars; if it already exists, regenerate a random character;

3. If the generated random character does not exist, add it into the $chars string.

The following is a sample code:

function generateRandomString($length) {
  $chars = "";

  while (strlen($chars) < $length) {
    $char = chr(mt_rand(65, 90)); // 生成65-90的随机数字
    if (strpos($chars, $char) === false) { // 判断$char是否已经在$chars中出现过
      $chars .= $char;
    }
  }

  return $chars;
}

echo generateRandomString(18);

In the above code, we use the mt_rand() function to generate a random number between 65 and 90, and then use the chr() function to convert this number to corresponding characters. Since the generated random string may be repeated, use the strpos() function to find whether the character already exists, and repeat the process of generating random characters and searching through the while loop until the total number of characters generated reaches the set length, and return result.

2. Use timestamps and random numbers to generate unique characters

The above method can already complete the function of generating unique characters, but due to the need to repeatedly search for the generated characters, it is necessary Computing power may be relatively high. In situations where concurrent access is high and the number of generated characters is large, performance problems are prone to occur.

Therefore, we can use the timestamp random number method to generate unique characters.

The following is the idea:

1. Generate a unique timestamp and convert it into a hexadecimal string;

2. Generate a four-digit Random string, add it to the front of the timestamp string to make it 20 digits long;

3. Use the substr() function to intercept the last 16 digits of the timestamp string as the generated random characters.

The following is a sample code:

function generateNonceStr($length = 18) {
  $timestamp = uniqid('', false);
  $nonce_str = substr($timestamp, 4) . substr(mt_rand(1000, 9999), 0, 4);
  return substr($nonce_str, -$length);
}

echo generateNonceStr();

In the above code, we first generate a 16-bit timestamp string, convert it into a 36-digit string, and then generate a timestamp string with a specified length random string. Finally, the two strings are concatenated, and the substr() function is used to obtain the subsequent substring of the specified length, which is the generated non-repeating character.

3. Summary

This article introduces two methods of generating unique characters, among which the method of using timestamps and random number generation is more practical and efficient. For scenarios such as generating order numbers in payment-related scenarios, more complete algorithms and rules should be used to ensure that the generated order numbers are not only non-duplicate, but also avoid the appearance of specific characters or numbers, reducing the risk of being attacked.

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