PHP生成短信验证码

简单版本

<?php
 function generate_code($length = 6) {
    $min = pow(10 , ($length - 1));
    $max = pow(10, $length) - 1;
    return rand($min, $max);
 }

复杂版本（java）

public static String createRandom(boolean numberFlag, int length){  
  String retStr = "";  
  String strTable = numberFlag ? "1234567890" : "1234567890abcdefghijkmnpqrstuvwxyz";  
  int len = strTable.length();  
  boolean bDone = true;  
  do {  
   retStr = "";  
   int count = 0;  
   for (int i = 0; i < length; i++) {  
    double dblR = Math.random() * len;  
    int intR = (int) Math.floor(dblR);  
    char c = strTable.charAt(intR);  
    if (('0' <= c) && (c <= '9')) {  
     count++;  
    }  
    retStr += strTable.charAt(intR);  
   }  
   if (count >= 2) {  
    bDone = false;  
   }  
  } while (bDone);  
  
  return retStr;  
 }