PHP: count_chars

Description

mixed count_chars ( string string [, int mode] )

Counts the number of occurrences of every byte-value (0..255) in string and returns it in various ways. The optional parameter mode defaults to 0. Depending on mode count_chars() returns one of the following:

0 - an array with the byte-value as key and the frequency of every byte as value.
1 - same as 0 but only byte-values with a frequency greater than zero are listed.
2 - same as 0 but only byte-values with a frequency equal to zero are listed.
3 - a string containing all used byte-values is returned.
4 - a string containing all not used byte-values is returned.

Example 1. count_chars() example

<?php $data = "Two Ts and one F."; $result = count_chars($data, 0); for ($i=0; $i < count($result); $i++) { if ($result[$i] != 0) echo "There were $result[$i] instance(s) of \"" , chr($i) , "\" in the string.\n"; } ?>
This will output :
There were 4 instance(s) of " " in the string. There were 1 instance(s) of "." in the string. There were 1 instance(s) of "F" in the string. There were 2 instance(s) of "T" in the string. There were 1 instance(s) of "a" in the string. There were 1 instance(s) of "d" in the string. There were 1 instance(s) of "e" in the string. There were 2 instance(s) of "n" in the string. There were 2 instance(s) of "o" in the string. There were 1 instance(s) of "s" in the string. There were 1 instance(s) of "w" in the string.

See also strpos() and substr_count().

User Contributed Notes
count_chars

Alex Gemmell
14-Feb-2005 12:03


Use: Great for checking for unique characters in a password.



I wanted to check that my website users, when registering a user account, chose a "valid" (not-so-easily-guessed) password.



One of the many checks was that the password must have 6 unique characters.  I was tying myself in knots with all kinds of recursive array calling when I was offered this wonderful one line solution:



function check_password($password) {



   #Have 6 unique characters

   if (count(count_chars($password, 1)) < 6) return false;



   #

   # other checks returning false as necessary

   #

   #



   return true;

}



I cannot claim this wonderful line for myself - a Mr Lynch suggested this to me.  Thanks!

seb at synchrocide dot net
16-May-2004 05:08


After much trial and error trying to create a function that finds the number of unique characters in a string I same across count_chars() - my 20+ lines of useless code were wiped for this:



<?

function unichar($string) {

$two= strtolower(str_replace(' ', '', $string));

$res = count(count_chars($two, 1));

return $res;

}



/* examples :: */



echo unichar("bob"); // 2

echo unichar("Invisibility"); //8

echo unichar("The quick brown fox slyly jumped over the lazy dog"); //26



?>



I have no idea where this could be used, but it's quite fun

mlong at mlong dot org
29-Jan-2002 06:27


// Usefulness of the two functions





<?php


 $string="aaabbc";





 // You just want to count the letter a


 $acount=substr_count($string,"a");





 // You want to count both letter a and letter b


 $counts=count_chars($string,0);


 $acount=$counts[ord("a")];


 $bcount=$counts[ord("b")];


?>

maotin at hongkong dot com
31-Jan-2001 07:04


Here are some more experiments on this relatively new and extremely handy function.





$string = 'I have never seen ANYTHING like that before! My number is "4670-9394".';





foreach(count_chars($string, 1) as $chr => $hit)


echo 'The character '.chr(34).chr($chr).chr(34).' has appeared in this string '.$hit.' times.<BR>';





#The result looks like


#The character " " has appeared in this string 11 times.





echo count_chars($string,3);


#The output is '!"-.034679AGHIMNTYabefhiklmnorstuvy'





echo strlen($string).' is not the same as '.strlen(count_chars($string, 3));





#This shows that '70 is not the same as 36'





As we can see above:





1)If you cares only about what is in the string, use count_chars($string, 1) and it will return an (associative?) array of what shows up only.





2) Either I misunderstood what the manul actually said, or it does not work the way it described: count_chars($strting, 3) actually returned a string of what characters are in the string, not a string of their byte-values (which is great because a string of numbers would be much harder to handle);





3)This is a short version of password checking: get the original string's length, then compare with the length of the string returned by count_chars($string,3).  





$length_of_string = strlen($string);


$num_of_chars = strlen(count_chars($string, 3));





$diff = ($length_of_string - $num_of_chars);





if ($diff)


echo 'At least one character has been used more than once.';


else


echo 'All character have been used only once.;





Note that since $num_of_chars gives no information about the actual number of occurance, we cannot go any further by the same rationale and say when $diff =2 then 2 characters showed up twice; it might be 1 character showd up 3 times, we have no way to tell (a good tolerance level setter, though).  You have to get the array and check the values if you want to have more control.





4) Final trick: now we have a primitive way to count the number of words in a string! (or do we have a fuction for that already?)