Count the number of times "world" occurs in the string in PHP

/*from www .jav a  2  s.  c o  m*/
<?php
    echo substr_count("Hello world. The world is nice","world");

    $str = "This is nice";
    echo strlen($str)."<br>"; // Using strlen() to return the string length
    echo substr_count($str,"is")."<br>"; // The number of times "is" occurs in the string
    echo substr_count($str,"is",2)."<br>"; // The string is now reduced to "is is PHP"
    echo substr_count($str,"is",3)."<br>"; // The string is now reduced to "s is PHP"
    echo substr_count($str,"is",3,3)."<br>"; // The string is now reduced to "s i"

    //Overlapped substrings:

    $str = "abcabcab";
    echo substr_count($str,"abcab"); // This function does not count overlapped substrings

    //If the start and length parameters exceeds the string length, this function will output a warning

    echo $str = "This is nice";
    substr_count($str,"is",3,9);
?>