ADOdb provides an internal debugging system that exposes the SQL commands used to execute a command, as well as other messages that can provide guidance when, for example, trying to establish a connection to the database. The earliest that debugging can be started is after instantiating the driver but before connection. In its simplest usage, debugging is enabled as follows:

include '/adodb-dir/adodb.inc.php';
 
$db = newAdoConnection('mysqli');
 
/*
* Initialize debugging
*/
$db->debug = true;
 
$db->connect('host','user','pass','database');

This might produce output something like:

-----<hr>
(mysqli): select * from usersx 
   
-----<hr>
Query: select * from usersx failed. Table 'db.usersx' doesn't exist
1146: Table 'db.usersx' doesn't exist
ADOConnection._Execute(select * from usersx, false)% line 1313, file: C:\dev\GitHub\ADOdb\adodb.inc.php
ADOConnection.Execute(select * from usersx)% line   46, file: C:\dev\tests\test7.php

The output is suitable for viewing in a browser, with messages from the database driver as well as backtrace data if there are problems. Note that debugging can be switched on and off during code execution as required.

The following alternative levels are available. Each produces a slightly different output.

The default logging behavior is to send all messages to STDOUT, but the behavior may be modified by either:

1. Defining a constant ADODB_OUTP which holds the name of the function that overrides the standard value
2. A variable $ADODB_OUTP which is globalized and achieves the same as above. This function can be dynamically changed.

The overriding function must accept 2 arguments:

1. A String which contains the message
2. A boolean which indicates whether to throw a newline. This may be discarded based on how the function works

DEFINE ('ADODB_OUTP','myLogger');
 
function myLogger($msg,$discard)
{
    print "\nThis is my messsage: $msg";
}