How to print debug information when debugging attr_get?

M66 2025-05-22

When debugging MySQLi preprocessing statements using the mysqli_stmt::attr_get function, developers often encounter problems such as unclear return values and inconsistent behavior. In order to improve debugging efficiency and locate problems, we can use some methods to print out detailed debugging information. This article will introduce several practical debugging techniques and combine PHP code examples to help you better understand the debugging process of mysqli_stmt::attr_get .

1. Understand the role of mysqli_stmt::attr_get

mysqli_stmt::attr_get is used to obtain the attribute value associated with the statement handle. Typically, it is used to check certain internal properties, such as settings for buffered queries:

 $attr_value = $stmt->attr_get(MYSQLI_STMT_ATTR_CURSOR_TYPE);

The return value may be an integer indicating the current state of the property. If false is returned, it means that the acquisition failed and further diagnosis is required.

2. Enable error reports and detailed logs

Before debugging, you should first make sure that PHP error reporting mechanism is enabled:

 mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
error_reporting(E_ALL);
ini_set('display_errors', 1);

This code will cause all MySQLi errors to throw exceptions and display them directly on the page, so that we can discover problems instantly.

3. Encapsulation and debugging auxiliary functions

To facilitate debugging the return value of attr_get , a helper function can be encapsulated:

 function debug_attr_get(mysqli_stmt $stmt, int $attr) {
    try {
        $value = $stmt->attr_get($attr);
        if ($value === false) {
            echo "Unable to get attributes（ID: $attr）: return false\n";
        } else {
            echo "property（ID: $attr）value: $value\n";
        }
    } catch (mysqli_sql_exception $e) {
        echo "Catch exceptions: " . $e->getMessage() . "\n";
    }
}

How to use:

 $mysqli = new mysqli("localhost", "user", "password", "database");
$stmt = $mysqli->prepare("SELECT * FROM users WHERE id = ?");
debug_attr_get($stmt, MYSQLI_STMT_ATTR_CURSOR_TYPE);

4. Combined with logging debugging information

In production environments, you may not want to output debug information directly to the front end. Debugging information can be retained by logging:

 function log_debug_info($message) {
    file_put_contents('/var/log/php_debug.log', date('Y-m-d H:i:s') . " - $message\n", FILE_APPEND);
}

Combine this with debugging functions:

 function debug_attr_get_to_log(mysqli_stmt $stmt, int $attr) {
    try {
        $value = $stmt->attr_get($attr);
        $msg = ($value === false) ? "attr_get return false" : "attr_get value为: $value";
    } catch (mysqli_sql_exception $e) {
        $msg = "abnormal: " . $e->getMessage();
    }
    log_debug_info("property ID $attr - $msg");
}

5. Simulate real environment debugging

Sometimes property settings may depend on other parameters of the connection or statement. For example:

 $stmt->attr_set(MYSQLI_STMT_ATTR_CURSOR_TYPE, MYSQLI_CURSOR_SCROLLABLE);

Only by calling attr_get can you observe the change in the attribute value. Therefore, it should be ensured that the execution logic of the actual application is simulated during debugging, rather than testing a certain function in isolation.

6. Debugging connection or statement failure

If prepare() is called returns false , the $stmt variable is an invalid object, and calling attr_get will cause a fatal error. To do this, you can add a check for connection and statement preparation:

 if (!$stmt) {
    die("Failed to prepare statement: " . $mysqli->error);
}

7. Use curl to simulate server requests for remote debugging

In some scenarios, you may need to remotely debug an API or server logic, and you can use curl to call PHP scripts for testing. For example:

 $url = "https://m66.net/api/debug_stmt.php";
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);
echo $response;

You can deploy the debugging code in a script under the m66.net domain name to observe the actual effect in conjunction with the log.

Conclusion

Through the above methods, you can more clearly understand the state and behavior of mysqli_stmt::attr_get at runtime. Debugging database operations is not just about whether SQL is executed successfully, but more importantly, it is about understanding the underlying behavior, especially when setting related functions using MySQLi properties. I hope the skills in this article can help you quickly locate problems and improve development efficiency.

mysqli_stmt::attr_get