Learn more about MATLAB

Debugging

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The MATLAB Debug Functions More Debug Functions The MATLAB Graphical Debugger A Quick Way to Examine Variables Setting Breakpoints from the Command Line Finding Line Numbers to Set Breakpoints Stopping Execution on an Error or Warning Locating an Error from the Error Message Using Warnings to Help Debug Making Code Execution Visible Debugging Scripts

The MATLAB Debug Functions

For a brief description of the main debug functions in MATLAB, type

help debug

For more information: See Debugging Process and Features in the MATLAB Desktop Tools and Development Environment documentation.

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More Debug Functions

Other functions you may find useful in debugging are listed below.

Function	Description
echo	Display function or script code as it executes.
disp	Display specified values or messages.
sprintf, fprintf	Display formatted data of different types.
whos	List variables in the workspace.
size	Show array dimensions.
keyboard	Interrupt program execution and allow input from keyboard.
return	Resume execution following a keyboard interruption.
warning	Display specified warning message.
MException	Access information on the cause of an error.
lastwarn	Return warning message that was last issued.

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The MATLAB Graphical Debugger

Learn to use the MATLAB graphical debugger. You can view the function and its calling functions as you debug, set and clear breakpoints, single-step through the program, step into or over called functions, control visibility into all workspaces, and find and replace strings in your files.

Start out by opening the file you want to debug using File > Open or the open function. Use the debugging functions available on the toolbar and pull-down menus to set breakpoints, run or step through the program, and examine variables.

For more information: See Debugging Process and Features in the MATLAB Desktop Tools and Development Environment documentation.

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A Quick Way to Examine Variables

To see the value of a variable from the Editor/Debugger window, hold the mouse cursor over the variable name for a second or two. You will see the value of the selected variable displayed.

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Setting Breakpoints from the Command Line

You can set breakpoints with dbstop in any of the following ways:

• Break at a specific M-file line number.

• Break at the beginning of a specific subfunction.

• Break at the first executable line in an M-file.

• Break when a warning, or error, is generated.

• Break if any infinite or NaN values are encountered.

For more information: See Setting Breakpoints in the MATLAB Desktop Tools and Development Environment documentation.

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Finding Line Numbers to Set Breakpoints

When debugging from the command line, a quick way to find line numbers for setting breakpoints is to use dbtype. The dbtype function displays all or part of an M-file, also numbering each line. To display delaunay.m, use

dbtype delaunay

To display only lines 35 through 41, use

dbtype delaunay 35:41

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Stopping Execution on an Error or Warning

Use dbstop if error to stop program execution on any error and enter debug mode. Use dbstop if warning to stop execution on any warning and enter debug mode.

For more information: See Debugging Process and Features in the MATLAB Desktop Tools and Development Environment documentation.

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Locating an Error from the Error Message

Click on the underlined text in an error message, and MATLAB opens the M-file being executed in its editor and places the cursor at the point of error.

For more information: See Finding Errors, Debugging, and Correcting M-Files in the MATLAB Desktop Tools and Development Environment documentation.

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Using Warnings to Help Debug

You can detect erroneous or unexpected behavior in your programs by inserting warning messages that MATLAB will display under the conditions you specify. See the section on Warning Control in the MATLAB Programming Fundamentals documentation to find out how to selectively enable warnings.

For more information: See the warning function reference page.

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Making Code Execution Visible

An easy way to see the end result of a particular line of code is to edit the program and temporarily remove the terminating semicolon from that line. Then, run your program and the evaluation of that statement is displayed on the screen.

For more information: See Finding Errors, Debugging, and Correcting M-Files in the MATLAB Desktop Tools and Development Environment documentation.

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Debugging Scripts

Scripts store their variables in a workspace that is shared with the caller of the script. So, when you debug a script from the command line, the script uses variables from the base workspace. To avoid errors caused by workspace sharing, type clear all before starting to debug your script to clear the base workspace.

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Program Development

Variables

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