Reference issues when passing mysqli_result across functions

M66 2025-05-28

In PHP, mysqli_result is the object type returned when executing database queries using the MySQLi extension. This object contains the data of the query result, which is usually created inside a function and may then be passed to other functions for processing.

However, in PHP, you sometimes encounter reference issues when passing objects, especially when you use the way references are passed. So, will there be a reference problem when passing mysqli_result between multiple functions? We will analyze it through the following aspects.

Reference pass with mysqli_result

In PHP, objects can be passed by reference. Reference passing means that the memory address of the object is passed, not a copy of the object. This leads to a problem: when you modify the content of an object within a function, other functions that reference the object will also perceive these modifications.

However, the behavior of the mysqli_result object is slightly special because it is a resource object returned after the MySQLi query is executed, and PHP will perform some internal optimization when processing this object.

1. Pass a reference to mysqli_result

When you pass mysqli_result as an argument to other functions, you can use the reference pass method:

 function fetchData($result) {
    while ($row = $result->fetch_assoc()) {
        echo $row['column_name'] . "\n";
    }
}

function processQueryResult(&$result) {
    fetchData($result);
}

In this case, $result is passed to fetchData and processQueryResult by reference, and in theory, if you modify the state of the object in one function, other functions should be able to perceive these changes.

2. Possible issues with reference passing

However, in some cases, if multiple functions refer to the same mysqli_result object at the same time, you may encounter the following problems:

Internal pointer to the object : mysqli_result has an internal pointer to track the cursor position of the data. When you call fetch_assoc() or other related mysqli_result method within a function, the cursor moves. If the same result set is processed concurrently in multiple functions, it may cause the cursor pointer to stay in unexpected places, resulting in the failure of subsequent functions to obtain data as expected.
Multiple iterations : mysqli_result does not support multiple independent iterations like arrays or other iterable objects. The pointer will automatically move forward every time the data acquisition method is called. Therefore, if one function consumes data, other functions can no longer access the remaining data.

Solution

To avoid problems caused by reference passing, there are several ways to effectively solve these potential problems.

1. Use a copy of mysqli_result

To ensure that each function accesses data independently and avoids pointer conflicts, the mysqli_result object can be copied before being passed to other functions. In this way, each function operates on a copy of the object, not the same reference.

 function fetchData($result) {
    while ($row = $result->fetch_assoc()) {
        echo $row['column_name'] . "\n";
    }
}

function processQueryResult($result) {
    $resultCopy = clone $result;  // Create a copy
    fetchData($resultCopy);
}

2. Re-execute the query

If the query result set has been consumed and you need to access the data again, you can choose to re-execute the query and return the new mysqli_result object. This is the safest way to avoid multiple accesses to the same object.

 function fetchData($result) {
    while ($row = $result->fetch_assoc()) {
        echo $row['column_name'] . "\n";
    }
}

function processQueryResult($mysqli, $query) {
    $result = $mysqli->query($query);
    fetchData($result);
}

This method ensures that every time the function is called, the new query results are operated on.

summary

The use of references does bring some potential problems when passing mysqli_result between multiple functions, especially when it comes to pointers and data consumption within objects. The best way to do this is to avoid passing references directly, try to use a copy, or re-execute the query when needed to get a new mysqli_result object.

By correctly managing the transfer and operation of mysqli_result object, you can avoid common problems in reference delivery and ensure that the program can run stably.

mysqli_result