尽管条件仍然为真，为什么这个 for 循环似乎没有执行？

Question

In the following SSCCE, why isn't the for loop being executed for $a greater than 3, although the condition should let it execute till $a becomes 5.

And the output of the last statement is even more weird.

What I am trying to achieve is that I want to delete the elements have the Select one value for the element/variable word , such that the resulting array is:

Array ( [0] => stdClass Object ( [word] => alpha [sentence] => A is the first letter in the word Alpha. ) [1] => stdClass Object ( [word] => beta [sentence] => B is the first letter in the word Beta. ) )

The question is that what is messing it up and what can I do to fix it?

<?php 

$objectOne = new stdClass;
$objectOne->word = 'alpha';
$objectOne->sentence = 'A is the first letter in the word Alpha.';

$objectTwo = new stdClass;
$objectTwo->word = 'beta';
$objectTwo->sentence = 'B is the first letter in the word Beta.';

$objectThree = new stdClass;
$objectThree->word = 'Select one';
$objectThree->sentence = '';

$items = array($objectOne, $objectTwo, $objectThree, $objectThree, $objectThree, $objectThree );


print_r($items);//check
echo '<br><br>count($items) >> '.count($items).'<br><br>';//check


for ($a=0; $a < count($items); $a++) {
    echo '<br><br>We are entering index '.$a.'<br><br>';//check
    echo '<br>'.$items[$a]->word.'<br>';//check

    if ( ($items[$a]->word)=="Select one"  ) {
        echo '<br>YES if ( ($items['.$a.']->word)=="Select one"  ) AT '.$a.' INDEX.<br>';//check
        unset($items[$a]);
        /**/array_splice($items, $a, 1);
    }

    echo '<br><br>We are leaving index '.$a.'<br><br>';//check
}


echo '<br><br>AFTER:-<br>';//check
print_r($items);//check

?>

OUTPUT:

Array ( [0] => stdClass Object ( [word] => alpha [sentence] => A is the first letter in the word Alpha. ) [1] => stdClass Object ( [word] => beta [sentence] => B is the first letter in the word Beta. ) [2] => stdClass Object ( [word] => Select one [sentence] => ) [3] => stdClass Object ( [word] => Select one [sentence] => ) [4] => stdClass Object ( [word] => Select one [sentence] => ) [5] => stdClass Object ( [word] => Select one [sentence] => ) )

count($items) >> 6



We are entering index 0


alpha


We are leaving index 0



We are entering index 1


beta


We are leaving index 1



We are entering index 2


Select one

YES if ( ($items[2]->word)=="Select one" ) AT 2 INDEX.


We are leaving index 2



We are entering index 3


Select one

YES if ( ($items[3]->word)=="Select one" ) AT 3 INDEX.


We are leaving index 3



AFTER:-
Array ( [0] => stdClass Object ( [word] => alpha [sentence] => A is the first letter in the word Alpha. ) [1] => stdClass Object ( [word] => beta [sentence] => B is the first letter in the word Beta. ) [2] => stdClass Object ( [word] => Select one [sentence] => ) ) 

Answer 1

Use a temp variable for iteration as you unset the key of main during the for execution. Maybe, this should work :-

$temp = $items;
for ($a=0; $a < count($temp); $a++) {
  echo '<br><br>We are entering index '.$a.'<br><br>';//check
  echo '<br>'.$items[$a]->word.'<br>';//check

  if ( ($items[$a]->word)=="Select one"  ) {
      echo '<br>YES if ( ($items['.$a.']->word)=="Select one"  ) AT '.$a.' INDEX.<br>';//check
      unset($items[$a]);
      /**/array_splice($items, $a, 1);
  }

  echo '<br><br>We are leaving index '.$a.'<br><br>';//check
}

Answer 2

The condition is not always true. The condition in your for loop recalculates the size of the array in each iteration. The length of the array changes whenever an item is removed.

The value of $a and count($items) each time the condition is checked is as follows:

$a | count($items) | $a < count($items)
---------------------------------------
 0 | 6             | true 
 1 | 6             | true
 2 | 6             | true
 3 | 5             | true  -- $items[2] was removed
 4 | 4             | false -- $items[3] was removed

You should store the size of the array in a variable and use that instead. Also since array_splice doesn't preserve numeric keys you will eventually get an undefined offset notice when trying to access $items[4] and $items[5] . That line is not required.

$count = count($items);
for ($a=0; $a < $count; $a++) {

Better yet you can use a foreach instead of the for and use $item instead of $items[$a] :

foreach ($items as $a=>$item) {
    echo '<br><br>We are entering index '.$a.'<br><br>';//check
    echo '<br>'.$item->word.'<br>';//check
    ...
    unset($items[$a]); //can't use $item because it is a copy and not a reference