Php recursive function return null while variable have value

Question

This function returns NULL while $alias having a value in the second recursion.

In the first call, it returns the required value, but when the first if does not match and it recurse first, the required value is available in the $alias variable, but it does not return anything.

public function checkAlias($fname='', $lname='') {

    if(!empty($fname)) {
        $fname = mysql_real_escape_string($fname);
    }

    if(!empty($lname)) {
        $lname = mysql_real_escape_string($lname);
    }

    $alias = strtolower($fname).strtolower($lname);
    $sql = "Select ALIAS from table where ALIAS = '$alias'";
    $query = mysql_query($sql);
    $row = mysql_fetch_row($query);
    $string_length = strlen($alias) - 1;
    $result_string = substr($alias, 0, $string_length);

    if(!$row) {
        print $alias;   // Is printing value
        return $alias;  // But here it returns null
    }
    else {
        $this->checkAlias($result_string);
    }

}

maybe you forgot a return before this line: `$this->checkAlias($result_string);`? — bwoebi, Sep 16 '13 at 12:19

score 12 · Accepted Answer · answered Sep 16 '13 at 12:22

12

You forgot to return the result of the recursion call:

return $this->checkAlias($result_string);

answered Sep 16 '13 at 12:22

Gerald Schneider

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score 3 · Answer 2 · edited Jun 01 '22 at 19:50

You forgot the return keyword before $this->checkAlias($result_string);

Change your code to this:

public function checkAlias($fname='', $lname='') {

    if(!empty($fname)) {
        $fname = mysql_real_escape_string($fname);
    }

    if(!empty($lname)) {
        $lname = mysql_real_escape_string($lname);
    }

    $alias = strtolower($fname).strtolower($lname);
    $sql = "Select ALIAS from table where ALIAS = '$alias'";
    $query = mysql_query($sql);
    $row = mysql_fetch_row($query);
    $string_length = strlen($alias) - 1;
    $result_string = substr($alias, 0, $string_length);

    if(!$row) {
        print $alias;   // Is printing value
        return $alias;  // But here it returns null
    }
    else {
        return $this->checkAlias($result_string);
    }
}

Because the first time the code will reach the else statement, and the second time it runs it will go in the if statement. The if returns the value, but in the else you don't do anything with it, so it returns it and you get your value.

Php recursive function return null while variable have value

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