MikeMikeMike Posted April 16, 2011 Share Posted April 16, 2011 My question relates to the code for view_tasks2.php (copied below) on or about page 35 in larry's book. About 3/4 of the way down the code you will see this snippet // Complete the query and execute: $q = substr($q, 0, -2) . ')'; $r = mysqli_query($dbc, $q); I am wondering why he's decided to set the substr parameters to 0 and -2. I believe -2 in this case will mean that it finishes 2 from the end of the length of q, but why do that? Thanks if you can help. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="content-type" content="text/html; charset=iso-8859-1" /> <title>View Tasks</title> </head> <body> <h3>Current To-Do List</h3> <?php # Script 1.5 - view_tasks2.php /* This page shows all existing tasks. * A recursive function is used to show the * tasks as nested lists, as applicable. * Tasks can now be marked as completed. */ // Function for displaying a list. // Receives one argument: an array. function make_list ($parent) { // Need the main $tasks array: global $tasks; // Start an ordered list: echo '<ol>'; // Loop through each subarray: foreach ($parent as $task_id => $todo) { // Display the item: // Start with a checkbox! echo <<<EOT <li><input type="checkbox" name="tasks[$task_id]" value="done" /> $todo EOT; // Check for subtasks: if (isset($tasks[$task_id])) { // Call this function: make_list($tasks[$task_id]); } // Complete the list item: echo '</li>'; } // End of FOREACH loop. // Close the ordered list: echo '</ol>'; } // End of make_list() function. // Connect to the database: $dbc = @mysqli_connect ('localhost', 'root', 'root', 'test', 8889) OR die ('<p>Could not connect to the database!</p></body></html>'); // Check if the form has been submitted: if (isset($_POST['submitted']) && isset($_POST['tasks']) && is_array($_POST['tasks'])) { // Define the query: $q = 'UPDATE tasks SET date_completed=NOW() WHERE task_id IN ('; // Add each task ID: foreach ($_POST['tasks'] as $task_id => $v) { $q .= $task_id . ', '; } // Complete the query and execute: $q = substr($q, 0, -2) . ')'; $r = mysqli_query($dbc, $q); // Report on the results: if (mysqli_affected_rows($dbc) == count($_POST['tasks'])) { echo '<p>The task(s) have been marked as completed!</p>'; } else { echo '<p>Not all tasks could be marked as completed!</p>'; } } // End of submission IF. // Retrieve all the uncompleted tasks: $q = 'SELECT task_id, parent_id, task FROM tasks WHERE date_completed="0000-00-00 00:00:00" ORDER BY parent_id, date_added ASC'; $r = mysqli_query($dbc, $q); // Initialize the storage array: $tasks = array(); while (list($task_id, $parent_id, $task) = mysqli_fetch_array($r, MYSQLI_NUM)) { // Add to the array: $tasks[$parent_id][$task_id] = $task; } // For debugging: //echo '<pre>' . print_r($tasks,1) . '</pre>'; // Make a form: echo '<p>Check the box next to a task and click "Update" to mark a task as completed (it, and any subtasks, will no longer appear in this list).</p> <form action="view_tasks2.php" method="post"> '; // Send the first array element // to the make_list() function: make_list($tasks[0]); // Complete the form: echo '<input name="submitted" type="hidden" value="true" /> <input name="submit" type="submit" value="Update" /> </form> '; ?> </body> </html> Link to comment Share on other sites More sharing options...
Jonathon Posted April 16, 2011 Share Posted April 16, 2011 I looked at something similar the other day and had to take a step back to make sure I followed it right. From what I surmised, the $q isn't completed initially, it ends mid way through completion, the -2 does remove the last 2 charachters of $q in this case ' ; then the foras loop is completed adding to the query and then the query is ended finally. If he didn't do that then either the $q would fail initially as it isn't terminated correctly initially I.e its missing the ' and the ; or after the foras loop the query would have 'insert query string here'; and then larry couldn't append extra to the query because it would already be completed from the previous step. This what I understood it to be, correct me if I'm wrong though 1 Link to comment Share on other sites More sharing options...
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