PHP计算产生负数？

Question

具有下列值：

$a[0] = "4:00:00 am"
$b[0] = "8:00:00 am"
$c[0] = "9:00:00 am"
$d[0] = "1:22:00 pm"

为什么第二个if语句会导致-8值被写入数据库？第一个if语句产生适当的4小时值，但第二个语句没有。是因为上午/下午的变化还是什么原因？

if (!$a[0]=="" AND !$b[0]=="") {
   $start = explode(':', $a[0]);
   $end = explode(':', $b[0]);
   $total_hours = $end[0] - $start[0] - ($end[1] < $start[1]);
   mysqli_query($con,"UPDATE timeclock SET daily_hours='$total_hours' WHERE idex='$data[idex]' AND date='$date' AND status='slunch'");
}

if (!$c[0]=="" AND !$d[0]=="") {
   $start = explode(':', $c[0]);
   $end = explode(':', $d[0]);
   $total_hours = $end[0] - $start[0] - ($end[1] < $start[1]);
   mysqli_query($con,"UPDATE timeclock SET daily_hours='$total_hours' WHERE idex='$data[idex]' AND date='$date' AND status='ework'");
}

Answer 1

因为下午1点到9点相当于-8的1 - 9。您需要将PM时间转换为24小时制，例如

1pm -> 13
9am -> 9

13 - 9 = 4

Answer 2

您的代码完全按照预期的方式工作。只是你在减去时间，而不是把它转换成24小时制。

您可以使用date()进行转换，如下所示：

$time_in_24 = date("H:i", strtotime("1:22:00 pm")); // 13:22

将您的代码更改为：

$a[0] = date("H:i", strtotime("4:00:00 am"));  
$b[0] = date("H:i", strtotime("8:00:00 am"));  
$c[0] = date("H:i", strtotime("9:00:00 am"));  
$d[0] = date("H:i", strtotime("1:22:00 pm"));  

这应该可以解决这个问题。

代码板：

Answer 3

$a[0] = "4:00:00 am";
$b[0] = "8:00:00 am";
$c[0] = "9:00:00 am";
$d[0] = "1:22:00 pm";
if (!$a[0]=="" AND !$b[0]=="") {
   $start = convert($a[0]);
   $end = conver($b[0]);
   $total_hours = $end[0] - $start[0] - ($end[1] < $start[1]);
   mysqli_query($con,"UPDATE timeclock SET daily_hours='$total_hours' WHERE idex='$data[idex]' AND date='$date' AND status='slunch'");
}

if (!$c[0]=="" AND !$d[0]=="") {
   $start = convert($c[0]);
   $end = convert($d[0]);
   $total_hours = $end[0] - $start[0] - ($end[1] < $start[1]);
   mysqli_query($con,"UPDATE timeclock SET daily_hours='$total_hours' WHERE idex='$data[idex]' AND date='$date' AND status='ework'");
}

function convert($hour){
    $m = strtolower(substr($hour, -2));//am or pm
    $hr = array_slice(explode(':', $hour), 0, 2);
    if ($m == 'pm') $hr[0] += 12;
    return $hr;
}