PHP跟踪最后的x次迭代

Question

I have four variables: $one_flag, $two_flag, $three_flag, and $four_flag. I'm using them as flags inside a for loop because I want to keep track of the last four iterations.

$one_flag = 1;
$two_flag = 0;
$three_flag = 0;
$four_flag = 0;

$a = array(1, 2, 3, 17, 27, 44, 45, 47, 49);

foreach ($a as $v) {
    if ($one_flag){
        $first_v = $v;
        $one_flag = 0;
        $two_flag = 1;
    }
    if ($two_flag){
        $second_v = $v;
        $two_flag = 0;
        $three_flag = 1;
    }
    if ($three_flag){
        $third_v = $v;
        $three_flag = 0;
        $four_flag = 1;
    }
    if ($four_flag){
        $fourth_v = $v;
        $four_flag = 0;
        $first_flag = 1;
    }
    if ($v == 45){
        # tricky part
        print "The last three v's were: " . $first_v . ", " . $second_v . ", " . $third_v . "
";
    }
}

Right now it prints The last three v's were 1, 1, 1 but it's supposed to print The last three v's were 45, 44, 27. Also, the problem with the code above is I need to know which flag is equal to 1 (what flag we're currently on) so that I can print the correct statement.

For example, when $v == 45, $first_v is suppose to equal to 27; $second_v is suppose to equal to 44; $fourth_v is suppose to equal to 17; and third_v is suppose equal to 45. I'd need to know $three_flag is equal to 1 in order to print out "The last three were $second_flag, $first_flag, $fourth_flag" in that order.

How can I get my loop to work? How do I keep track of the last four iterations?

EDIT: I misspoke. I actually want to print The last three v's were 44, 27, 17

Answer 1

I suppose that this is a minimal example and that the real program is more complex. Otherwise, you could just get the length of the array and retrieve the last 3 elements based on it.

I'd change the approach as follow:

$f1 = -1;  // Last value read
$f2 = -1;  // second to last value
$f3 = -1;


$a = array(1, 2, 3, 17, 27, 44, 45, 47, 49);

foreach ($a as $v) {
    $f3 = $f2;
    $f2 = $f1;
    $f1 = $v;
    if ($v == 45){
        # tricky part
        print "The last three v's were: " . $f1 . ", " . $f2 . ", " . $f3 . "
";
    }
}

I'm using -1 as an indicator that nothing was assigned to the variable. You should adapt this to your context if needed.