Question

我正在尝试使用isset（）可视化PHP中的变量，当我不使用它时，会出现一条通知，指出该索引未定义。

我正在尝试使用上述函数在表中输出变量，但是有了它，表将不输出任何值。

[

<?php
                        // Include config file
                        require_once "config.php";

                        // Attempt select query execution
                        $sql = "SELECT * FROM courses";
                        if($result = $pdo->query($sql)){
                            if($result->rowCount() > 0){
                                echo "<table class='table table-bordered table-striped'>";
                                    echo "<thead>";
                                        echo "<tr>";
                                            echo "<th>#</th>";
                                            echo "<th>Enquiry ID</th>";
                                            echo "<th>Course Name</th>";
                                            echo "<th>Course Level</th>";
                                            echo "<th>Action</th>";
                                        echo "</tr>";
                                    echo "</thead>";
                                    echo "<tbody>";
                                    while($row = $result->fetch()){
                                        echo "<tr>";
                                            echo "<td>" . isset($row\['courseid'\]) . "</td>";
                                            echo "<td>" . isset($row\['enquiryid'\]) . "</td>";
                                            echo "<td>" . isset($row\['coursename'\]) . "</td>";
                                            echo "<td>" . isset($row\['courselevel'\]) . "</td>";
                                            echo "<td>";
                                                echo "<a href='read.php?id=". isset($row\['courseid'\]) ."' title='View Record' data-toggle='tooltip'><span class='glyphicon glyphicon-eye-open'></span></a>";
                                                echo "<a href='update.php?id=". isset($row\['courseid'\]) ."' title='Update Record' data-toggle='tooltip'><span class='glyphicon glyphicon-pencil'></span></a>";
                                                echo "<a href='delete.php?id=". isset($row\['courseid'\]) ."' title='Delete Record' data-toggle='tooltip'><span class='glyphicon glyphicon-trash'></span></a>";
                                            echo "</td>";
                                        echo "</tr>";
                                    }
                                    echo "</tbody>";                            
                                echo "</table>";
                                // Free result set
                                unset($result);
                            } else{
                                echo "<p class='lead'><em>No records were found.</em></p>";
                            }
                        } else{
                            echo "ERROR: Could not able to execute $sql. " . $mysqli->error;
                        }

                        // Close connection
                        unset($pdo);
                        ?>

] 1

我希望输出数据库表中包含的值，但是这些字段仍为空白。

Answer 1

isset()返回true或false。您无法直接将其回显。您需要一个条件条件，该条件条件使用isset()来检查变量并将其显示为true。

假设您正在运行PHP 7，则可以使用null合并运算符。这是三元数的简写形式，根据是否设置了变量，该三元数会导致变量或空白字符串的出现：

echo "<td>" . $row['courseid'] ?? '' . "</td>";

文档：https://php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op

这等效于：

echo "<td>" . isset($row['courseid']) ? $row['courseid'] : '' . "</td>";

但是，如果您被迫使用该三元方法，为了方便起见，我可能会将其包装在一个函数中。

Answer 2

此isset()函数返回True / False，因此您不能直接echo将该值删除。

因此最好在isset()

中使用单行条件

就像我在下面写的

echo "<td>" . isset($row['courseid']) ? $row['courseid'] : 'Not Set' . "</td>";

Answer 3

我以您的while循环为例：

 while($row = $result->fetch()){
                                    echo "<tr>";
                                    if (isset($row['courseid'])){
                                        echo "<td>" . $row['courseid']) . "</td>";
                                    } else {
                                        echo "<td>" . 'NOT SET' . "</td>";
                                    } 

                                    if (isset($row['enquiryid'])){
                                        echo "<td>" . $row['enquiryid'] . "</td>";
                                    } else {
                                        echo "<td>" . 'NOT SET' . "</td>";
                                    }

                                    if (isset($row['coursename'])){
                                        echo "<td>" . $row['coursename']. "</td>";
                                    } else {
                                        echo "<td>" . 'NOT SET' . "</td>";
                                    }

                                    if (isset($row['courselevel'])){
                                        echo "<td>" . $row['courselevel']) . "</td>";
                                    } else {
                                        echo "<td>" . 'NOT SET' . "</td>";
                                    }

                                        echo "<td>";
                                            echo "<a href='read.php?id=". $row['courseid'] ."' title='View Record' data-toggle='tooltip'><span class='glyphicon glyphicon-eye-open'></span></a>";
                                            echo "<a href='update.php?id=". $row['courseid'] ."' title='Update Record' data-toggle='tooltip'><span class='glyphicon glyphicon-pencil'></span></a>";
                                            echo "<a href='delete.php?id=". $row\'courseid'] ."' title='Delete Record' data-toggle='tooltip'><span class='glyphicon glyphicon-trash'></span></a>";
                                        echo "</td>";
                                    echo "</tr>";
                                }

希望有帮助

有没有一种方法可以使用isset（）在PHP中输出变量？

3 个答案: