Warning Control Statements :: Error Handling (Programming)

Programming

Warning Control Statements

Once you have the warning statements in your M-file code and are ready to execute the code, you can indicate how you want MATLAB to act on these warnings by issuing control statements. These statements place the specified warning(s) into a desired state and have the format

```
warning state msg_id
```

Control statements can also return information on the state of selected warnings. This only happens if you assign the output to a variable, as shown below. See Output from Control Statements.

```
s = warning('state', 'msg_id');
```

Warning States

There are three possible values for the state argument of a warning control statement.

State
Description

on
Enable the display of selected warning message.

off
Disable the display of selected warning message.

query
Display the current state of selected warning.

State	Description
`on`	Enable the display of selected warning message.
`off`	Disable the display of selected warning message.
`query`	Display the current state of selected warning.

Message Identifiers

In addition to the message identifiers already discussed, there are two other identifiers that you can use in control statements only.

Identifier
Description

msg_id string
Set selected warning to the specified state.

all
Set all warnings to the specified state.

last
Set only the last displayed warning to the specified state.

Identifier	Description
`msg_id string`	Set selected warning to the specified state.
`all`	Set all warnings to the specified state.
`last`	Set only the last displayed warning to the specified state.

Note MATLAB starts up with all warnings enabled, except for those that are displayed in response to the command, warning('query', 'all').

Example 1 -- Enabling a Selected Warning

Enable just the actionNotTaken warning from Simulink by first turning off all warnings and then setting just that warning to on.

warning off all
warning on Simulink:actionNotTaken

Use query to determine the current state of all warnings. It reports that you have set all warnings to off with the exception of Simulink:actionNotTaken.

warning query all
The default warning state is 'off'. Warnings not set to the 
default are

  State  Warning Identifier

     on  Simulink:actionNotTaken

Example 2 -- Disabling the Most Recent Warning

Evaluating inv on zero displays a warning message. Turn off the most recently invoked warning with warning off last.

inv(0)
Warning: Matrix is singular to working precision.
ans =
   Inf

warning off last

inv(0)                      % No warning is displayed this time
ans =
   Inf

Warning Statements Output from Control Statements