## Example

`

     mixed count_chars ( string $string [, int $mode = 0 ] )

`

## Description

Counts the number of occurrences of every byte-value (0..255) in string and returns it in various ways.

## Return Values

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 unique characters is returned. 4 - a string containing all not used characters is returned.