---
id: exceptions
title: Exceptions
sidebar_label: Exceptions
---

BlitzMax provides a mechanism for handling runtime errors known as **exception handling**.

An exception is actually just an object. You can **throw** and **catch** exceptions using the [Throw] command and a [Try] /
[Catch] block. Here is a simple example:

```blitzmax
Function ExTest()
    Throw "Bingo!"
End Function

Try
    ExTest()
Catch ex:Object
    Print ex.ToString()
End Try
```
Throwing an exception causes the program to jump to the most recent [Catch] block. You can provide multiple catch blocks
for catching exceptions of different types. If there is no appropriate [Catch] block for the exception, then the program
jumps to the %next most recent [Catch] block. If no catch block can be found to deal with the exception, the program
will end.

BlitzMax has several built-in exception types, all of which extend type TBlitzException. These are:

| Exception  | Cause  |
|---|---|
| TNullMethodException  | Thrown when a program attempts to call an abstract method.  |
| TNullFunctionException  | Thrown when a program attempts to call a null function.  |
| TNullObjectException  | Thrown when a program attempts to access a null object (only thrown in debug mode).  |
| TArrayBoundsException  | Thrown when a program attempts to access an array element outside of an array's bounds (only thrown in debug mode).  |
| TRuntimeException  | Thrown by the [RuntimeError] or [Assert] commands.  |

[Throw]: ../../api/brl/brl.blitz/#throw
[Try]: ../../api/brl/brl.blitz/#try
[Catch]: ../../api/brl/brl.blitz/#catch
[RuntimeError]: ../../api/brl/brl.blitz/#function-runtimeerror-message
[Assert]: ../../api/brl/brl.blitz/#assert