PHP: variable value mysteriously set to 0

问题

Thanks in advance for your help! I have a situation I'm trying to debug where a variable is mysteriously set to 0.

I know from xdebug (using PHPStorm) that it happens at this specific line:

// breakpoint here: $id_key is 'my_entity_id_key'
$e_entity_ids = my_module_fetch_col_keyed($query, $id_key, $created_column);
// breakpoint here: $id_key is 0

It's weird, because $id_key is not a reference, nor does the function take a reference as a parameter. Also, after the value has changed to 0, $id_key is blue in the variables pane of the debugger.

I've tried making a copy of the variable and using it to pass to the function instead:

$id_key2 = $id_key;
$e_entity_ids = my_module_fetch_col_keyed($query, $id_key2, $created_column);
// breakpoint here: $id_key is 0, and so is $id_key2

I'm wondering:

How could the value of $id_key be mysteriously changing to 0?
How can I create a copy of $id_key so that it's not changed when I pass the copy to my_module_fetch_col_keyed()?
What does it mean when a variable name is blue in the variables pane in PHPStorm?

When I step into my_module_fetch_col_keyed(), there's a line after which $column is mysteriously 0, as shown:

function my_module_fetch_col_keyed($query, $column, $key_column = NULL) {
  try {
    $result = $query->execute();
  }
  catch (Exception $e) {
    return FALSE;
  }

  if (!isset($key_column)) {
    try {
      // breakpoint here: $column is 'my_entity_id_key'
      $column_results = $result->fetchCol($column);
      // breakpoint here: $column is mysteriously 0
    }
    catch (Exception $e) {
      return FALSE;
    }
    return $column_results;
  }

  try {
    $assoc = $result->fetchAllAssoc($key_column);
  }
  catch (Exception $e) {
    return FALSE;
  }

  $keyed = array();
  foreach ($assoc as $key => $result) {
    $keyed[$key] = $result->{$column};
  }

  return $keyed;
}

and that $result->fetchCol() function is just a one liner that calls PDOStatement::fetchAll():

class DatabaseStatementBase extends PDOStatement implements DatabaseStatementInterface {

  [...]

  public function fetchCol($index = 0) {
    return $this->fetchAll(PDO::FETCH_COLUMN, $index);
  }

  // function fetchAll() is not overridden from parent PDOStatement

  [...]

}

EDIT: I tried putting $id_key as an object property and using the magic __set() method to get a backtrace and find out when exactly the variable is changed:

class Test {
  private $id_key;
  protected $values = array();
  public function __set($key, $value) {
    if ($key == 'id_key') {
      $b = debug_backtrace();
      "Hello World!";
    }

    if (method_exists(get_parent_class($this), '__set')) {
      return parent::__set($key, $value);
    }

    return $this->values[$key] = $value;
  }
  public function __get($key) {
    return isset($this->values[$key]) ? $this->values[$key] : 1;
  }
}

and then I updated my code like so:

$e_entity_ids = basic_functions_fetch_col_keyed($query, $test->id_key, $created_column);

Everything keeps working the same way it was, and $test->id_key evaluates to my_entity_id_key before and 0 after. I set breakpoints with in the __set() and __get() methods, and examined the values when they were called (for example, in the above line the get is called in basic_functions_fetch_col_keyed($query, $test->id_key, $created_column)). But, weirdly, THE __set() MAGIC FUNCTION WAS NOT CALLED when the value was set to 0. I'm so lost! Any help would be so appreciated!!

回答1:

It sure does look to me that id_key is being passed by reference.

Some of those PDO libraries are coded in C. It's quite possible that in the innards the variables get corrupted there.

TBF you're passing a string as an argument that expects a numeric value, so from the standpoint of the functions you're using, the new value is the same as the old value (most text strings not containing digits = 0).

来源：https://stackoverflow.com/questions/36730743/php-variable-value-mysteriously-set-to-0

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