A simple string generator in C++

Introduction

When we search something such as an user account in server, we need to generate strings for checking (I call them seeds). And from the following code, you can get a sequential string. This is something like that: if you initialize your seed sting with 'ab', the following will give you ac,ad,...az,aaa,aab... over and over all of the possible combinations in ch[0x100] except '\0'. What you need to do is to choose a char collection, to say, who will join in the permutation; this is a repeated combination, if you want unrepeated, then you can Google for it, I had seen it once, but I can't remember it now.

Using the code

So if you need a repeated permutation, you can consider to use the following code snippet. Firstly, you choose char collection, and initialize it, here I use [a-z]. After that, you need to initialize the seed. then the code will enter cycle, to get out the next combination for you. the result string are kept in szitem. You can use it in your search string. e.g. you can make it to be "rcpt to:<" + szitem + "@maildomain.com>\r\n", and send out to the smtp server. If you want ANSI string, you can change it accordingly, here I use UNICODE. I don't think you still need me to do that :-) anyway, if there is something needed, just drop me a line.

#define ENUMCHARCOUNT 26

WCHAR ch[0x100];

for(int i=0;i<ENUMCHARCOUNT;i++)
 ch[i] = L'a'+i;
for(int i=ENUMCHARCOUNT;i<0x100;i++)
 ch[i] = L'\0';

// the maximum length of result string seeds is 10.
unsigned short seed[10];
for(int j=0;j<10;j++)
 seed[j] = 0xff;

WCHAR szitem[10];
// initialize the seed here. so we will start from "ab".
seed[0]= L'a';
seed[1]= L'b';
seed[2]= L'\0';
while(1)
{
 if(seed[0]==ENUMCHARCOUNT)
 {
  seed[0] = 0;
  int kk = 1;
  while(1)
  {
   seed[kk]++;
   if(seed[kk]==0x100) // upgrade
   {
    seed[kk] = 0;
    break;
   }
   else if(seed[kk]==ENUMCHARCOUNT) // flat add
   {
    seed[kk] = 0;
    kk++;
   }
   else
    break;
  }
 }

 j=0;
 while(1)
 {
  szitem[j] = ch[seed[j]];
  if(seed[j]==0xff)
    break;
  j++;
 }

 //
 // do sth with szitem
 //

 seed[0]++;
}

Before you do cool things with the generated string seed, you can use regexps or other formula to filter it, if the checking process is time consuming (it always be).

History

Several days before, I used this to get out named items from a script engine ;-) Last what you should do with this code snippet, is cut out the above code, paste into your app source, and set a breakpoint at the last line, press F5, when it stop, drag sztiem into your watch panel. Then you can see what the cycle does for you. The last word what I should say is, every one who have been working on a search engine, he must have done the same thing as above, but I can't find out if anyone posted it here. So I did it myself. Really appreciate all of your comments! Happy weekend guys!