Question

I have the following PHP code:

class SQLStatements {
    public function __construct($iName) {
        $this->name = $iName;
        $this->sqlStatement = array ();
    }

    public function addStatement($iSQLStatement) {
        $this->sqlStatement [] = $iSQLStatement;
    }

...other functions...
}

print_r ($ss);
$sqlStatements->addStatement ( $ss );   
print_r ($sqlStatements);

Output is:

SQLStatement Object
(
    [id] => 300
    [timestamp] => 201301090222
    [fixture] => Home v Away
    [outcome] => Home
    [fixtureDateTime] => 2013-01-11
    [bookmakerOdds] => Array
        (
            [0] => 2.15
            [1] => 2.22
            [2] => 2.05
            [3] => 2.05
            [4] => 2.15
            [5] => 2.20
            [6] => 2.14
        )

)
SQLStatements Object
(
    [name] => TheStatement
    [sqlStatement] => Array
        (
            [0] => SQLStatement Object
                (
                    [id] => 300
                    [timestamp] => 201301090222
                    [fixture] => Home v Away
                    [outcome] => Home
                    [fixtureDateTime] => 2013-01-11
                    [bookmakerOdds] => Array
                        (
                            [0] => 2.15
                            [1] => 2.22
                            [2] => 2.05
                            [3] => 2.05
                            [4] => 2.15
                            [5] => 2.20
                            [6] => 2.14
                        )

                )

        )

)
SQLStatement Object
(
    [id] => 300
    [timestamp] => 201301090222
    [fixture] => Home v Away
    [outcome] => Home v Away - Draw
    [fixtureDateTime] => 2013-01-11
    [bookmakerOdds] => Array
        (
            [0] => 3.50
            [1] => 3.50
            [2] => 3.40
            [3] => 3.40
            [4] => 3.30
            [5] => 3.50
            [6] => 3.28
        )

)
SQLStatements Object
(
    [name] => TheStatement
    [sqlStatement] => Array
        (
            [0] => SQLStatement Object
                (
                    [id] => 300
                    [timestamp] => 201301090222
                    [fixture] => Home v Away
                    [outcome] => Home v Away - Draw
                    [fixtureDateTime] => 2013-01-11
                    [bookmakerOdds] => Array
                        (
                            [0] => 3.50
                            [1] => 3.50
                            [2] => 3.40
                            [3] => 3.40
                            [4] => 3.30
                            [5] => 3.50
                            [6] => 3.28
                        )

                )

            [1] => SQLStatement Object
                (
                    [id] => 300
                    [timestamp] => 201301090222
                    [fixture] => Home v Away
                    [outcome] => Home v Away - Draw
                    [fixtureDateTime] => 2013-01-11
                    [bookmakerOdds] => Array
                        (
                            [0] => 3.50
                            [1] => 3.50
                            [2] => 3.40
                            [3] => 3.40
                            [4] => 3.30
                            [5] => 3.50
                            [6] => 3.28
                        )

                )

        )

)

$ss is a SQLStatement Object and the SQLStatements object is a collection of SQLStatement Objects. However as you can see from the output, SQLStatements->SQLStatement[0] and SQLStatements->SQLStatement[1] are the same. I am expecting SQLStatements->SQLStatement[0]->outcome to be ‘Home’, not ‘Home v Away – Draw’. What am I doing wrong?

Answer 1

When an object is passed to a method in PHP, PHP actually passes the value of that object’s address in memory. What that means is, when you call addStatement($ss), you’re not adding a copy of the $ss object to the statements array – you’re adding a pointer to that object in memory. If you later change the $ss object, it will also be changed on your array in the SQLStatements class (because they point to the same object in memory).

What you should be doing is, after calling addStatement($ss), you should do something like: $ss = new SQLStatement() and then you can make your changes and add it again (by creating a new SQLStatement() you have allocated another block of memory for this new object, and that location has a new memory address which won’t conflict with the old object that was assigned to $ss.)