Check Code for Errors and Warnings Using the Code Analyzer

The MATLAB^® Code Analyzer can automatically check your code for coding problems. You can view warning and error messages about your code, and modify your file based on the messages. The messages are updated automatically and continuously so you can see if your changes address the issues noted in the messages. Some messages offer additional information, automatic code correction, or both.

A list of all checks performed by the MATLAB Code Analyzer can be found here, Index of Code Analyzer Checks.

Enable Continuous Code Checking

To enable continuous code checking, on the Home tab, in the Environment section, click Preferences. Select MATLAB > Code Analyzer, and then select the Enable integrated warning and error messages check box. Set the Underlining option to Underline warnings and errors.

When continuous code checking is enabled, MATLAB displays warning and error messages about your code in the Editor and Live Editor. For example, the sample file lengthofline.m contains several errors and warnings. Copy the code into the Editor and save the file as lengthofline.m.

lengthofline.m Code

function [len,dims] = lengthofline(hline)
%LENGTHOFLINE Calculates the length of a line object
%   LEN = LENGTHOFLINE(HLINE) takes the handle to a line object as the
%   input, and returns its length.  The accuracy of the result is directly
%   dependent on the number of distinct points used to describe the line.
%
%   [LEN,DIM] = LENGTHOFLINE(HLINE) additionally tells whether the line is
%   2D or 3D by returning either a numeric 2 or 3 in DIM.  A line in a
%   plane parallel to a coordinate plane is considered 2D.
%
%   If HLINE is a matrix of line handles, LEN and DIM will be matrices of results.
%
%   Example:
%       figure; h2 = plot3(1:10,rand(1,10),rand(10,5));
%       hold on; h1 = plot(1:10,rand(10,5));
%       [len,dim] = lengthofline([h1 h2])

%   Copyright 1984-2004 The MathWorks, Inc. 

% Find input indices that are not line objects
nothandle = ~ishandle(hline);
for nh = 1:prod(size(hline))
    notline(nh) = ~ishandle(hline(nh)) || ~strcmp('line',lower(get(hline(nh),'type')));
end

len = zeros(size(hline));
for nl = 1:prod(size(hline))
    % If it's a line, get the data and compute the length
    if ~notline(nl)
        flds = get(hline(nl));
        fdata = {'XData','YData','ZData'};
        for nd = 1:length(fdata)
            data{nd} = getfield(flds,fdata{nd});
        end
        % If there's no 3rd dimension, or all the data in one dimension is
        % unique, then consider it to be a 2D line.
        if isempty(data{3}) | ...
               (length(unique(data{1}(:)))==1 | ...
                length(unique(data{2}(:)))==1 | ...
                length(unique(data{3}(:)))==1)
            data{3} = zeros(size(data{1}));
            dim(nl) = 2;
        else
            dim(nl) = 3;
        end
        % Do the actual computation
        temp = diff([data{1}(:) data{2}(:) data{3}(;)]);
        len(nl) = sum([sqrt(dot(temp',temp'))])
    end
end

% If some indices are not lines, fill the results with NaNs.
if any(notline(:))
    warning('lengthofline:FillWithNaNs', ...
        '\n%s of non-line objects are being filled with %s.', ...
        'Lengths','NaNs','Dimensions','NaNs')
    len(notline) = NaN;
    dim(notline) = NaN;
end
    
if nargout > 1
    dims = dim;
end

View Code Analyzer Status for File

When you open a file in the Editor or Live Editor, the message indicator at the top of the indicator bar shows the overall Code Analyzer status for the file.

Message Indicator	Description
	File contains syntax errors or other significant issues.
	File contains warnings or opportunities for improvement, but no errors.
	File contains no errors, warnings, or opportunities for improvement.
	Continuous code checking disabled.

For example, in lengthofline.m, the message indicator is , meaning that the file contains at least one error.

lengthofline file in the Editor with the red error symbol displayed in the indicator bar

View Code Analyzer Messages

To go to the first code fragment containing a message, click the message indicator. The identified code fragment is underlined in either red for errors or orange for warnings and improvement opportunities. If the file contains an error, clicking the message indicator brings you to the first error.

For example, in lengthofline.m, when you click the message indicator, the cursor moves to line 47, where the first error occurs. MATLAB displays the errors for that line next to the error marker in the indicator bar. Multiple messages can represent a single problem or multiple problems. Addressing one message might address all of them. Or, after you address one, the other messages might change or what you need to do can become clearer.

lengthofline file in the Editor after clicking the message indicator. Three errors display next to the error marker in the indicator bar.

To go to the next code fragment containing a message, click the message indicator. You also can click a marker in the indicator bar to go to the line that the marker represents. For example, click the first marker in the indicator bar in lengthofline.m. The cursor moves to the beginning of line 21.

To view the message for a code fragment, move the mouse pointer within the underlined code fragment. Alternatively, you can position your cursor within the underlined code fragment and press Ctrl+M. If additional information is available for the message, the message includes a Details button. Click the button to display the additional information and any suggested user actions.

lengthofline file in the Editor showing a warning message with a details button

Fix Problems in Code

For each message in your code file, modify the code to address the problem noted in the message. As you modify the code, the message indicator and underlining are updated to reflect changes you make, even if you do not save the file.

For example, on line 47 in lengthofline.m, the message suggests a delimiter imbalance. When you move the arrow keys over each delimiter, MATLAB does not appear to indicate a mismatch. However, code analysis detects the semicolon in data{3}(;) and interprets it as the end of a statement.

lengthofline file in the Editor after clicking the message indicator. Three errors display next to the error marker in the indicator bar.

To fix the problem in line 47, change data{3}(;) to data{3}(:). The single change addresses all of the messages on line 47, and the underline no longer appears for the line. Because the change removes the only error in the file, the message indicator at the top of the bar changes from to , indicating that only warnings and potential improvements remain.

For some messages, MATLAB suggests an automatic fix that you can apply to fix the problem. If an automatic fix is available for a problem, the code fragment is highlighted and the message includes a Fix button.

lengthofline file in the Editor showing a warning message with a fix button

For example, on line 27 in lengthofline.m, place the mouse over the underlined and highlighted code fragment prod. The displayed message includes a Fix button.

If you know how to fix the problem, perhaps from prior experience, click the Fix button or press Alt+Enter. If you are unfamiliar with the problem, right-click the highlighted code. The first item in the context menu shows the suggested fix. Select the item to apply the fix.

lengthofline file in the Editor showing the context menu. The first item in the menu is the suggested fix.

If multiple instances of a problem exist, MATLAB might offer to apply the suggested fix for all instances of the problem. To apply the fix for all instances of a problem, right-click the highlighted code and select Fix All (n) Instances of This Issue. This option is not available for all suggested fixes.

After you modify the code to address all the messages or disable designated messages, the message indicator becomes green. See the example file, lengthofline2.m, with all messages addressed.

lengthofline2.m Code

function [len,dims] = lengthofline2(hline)
%LENGTHOFLINE Calculates the length of a line object
%   LEN = LENGTHOFLINE(HLINE) takes the handle to a line object as the
%   input, and returns its length.  The accuracy of the result is directly
%   dependent on the number of distinct points used to describe the line.
%
%   [LEN,DIM] = LENGTHOFLINE(HLINE) additionally tells whether the line is
%   2D or 3D by returning either a numeric 2 or 3 in DIM.  A line in a
%   plane parallel to a coordinate plane is considered 2D.
%
%   If HLINE is a matrix of line handles, LEN and DIM will be matrices of results.
%
%   Example:
%       figure; h2 = plot3(1:10,rand(1,10),rand(10,5));
%       hold on; h1 = plot(1:10,rand(10,5));
%       [len,dim] = lengthofline([h1 h2])

%   Copyright 1984-2005 The MathWorks, Inc. 

% Find input indices that are not line objects
nothandle = ~ishandle(hline);
notline = false(size(hline));
for nh = 1:numel(hline)
    notline(nh) = nothandle(nh) || ~strcmpi('line',get(hline(nh),'type'));
end

len = zeros(size(hline));
dim = len;
for nl = 1:numel(hline)
    % If it's a line, get the data and compute the length
    if ~notline(nl)
        flds = get(hline(nl));
        fdata = {'XData','YData','ZData'};
        data = cell(size(fdata));
        for nd = 1:length(fdata)
            data{nd} = flds.(fdata{nd});
        end
        % If there's no 3rd dimension, or all the data in one dimension is
        % unique, then consider it to be a 2D line.
        if isempty(data{3}) || ...
               (length(unique(data{1}(:)))==1 || ...
                length(unique(data{2}(:)))==1 || ...
                length(unique(data{3}(:)))==1)
            data{3} = zeros(size(data{1}));
            dim(nl) = 2;
        else
            dim(nl) = 3;
        end
        % Do the actual computation
        temp = diff([data{1}(:) data{2}(:) data{3}(:)]);
        len(nl) = sum(sqrt(dot(temp',temp'))) %#ok<NOPRT>
    end
end

% If some indices are not lines, fill the results with NaNs.
if any(notline(:))
    warning('lengthofline2:FillWithNaNs', ...
        '\n%s of non-line objects are being filled with %s.', ...
        'Lengths','NaNs','Dimensions','NaNs')
    len(notline) = NaN;
    dim(notline) = NaN;
end
    
if nargout > 1
    dims = dim;
end

Analyze Files Using the Code Analyzer App

Since R2022b

You can create a report of Code Analyzer messages for all files in a folder using the Code Analyzer app.

To open the app:

MATLAB Toolstrip: On the Apps tab, under MATLAB, click the app icon: .
MATLAB command prompt: Enter codeAnalyzer.

Code Analyzer app showing an overall summary of code issues and code health details

Identify and Store Issues in Files With `codeIssues` Object

Since R2022b

You can use codeIssues to programmatically find and store issues in code. The codeIssues object stores issues found by the MATLAB Code Analyzer. The issues found in one or more specified files or folders can be sorted and filtered, either programmatically on the command line or interactively in the Code Analyzer app.

For example, you can generate a codeIssues object containing the issues in a specified file:

issues = codeIssues("test.m")

issues = 

  codeIssues with properties:

                         Date: 18-Oct-2022 14:18:54
                      Release: "R2023a"
                        Files: "C:\MyCode\test.m"
    CodeAnalyzerConfiguration: "active"
                       Issues: [3×10 table]
             SuppressedIssues: [0×11 table]


    Issues table preview

    Location    Severity    Fixability                                            Description                                             CheckID    LineStart    LineEnd    ColumnStart    ColumnEnd       FullFilename   
    ________    ________    __________    ____________________________________________________________________________________________    _______    _________    _______    ___________    _________    __________________

    "test.m"      info        manual      "Variable appears to change size on every loop iteration. Consider preallocating for speed."    AGROW          3           3            1             3        "C:\MyCode\test.m"
    "test.m"      info        auto        "Add a semicolon after the statement to hide the output (in a script)."                         NOPTS          6           6            3             3        "C:\MyCode\test.m"
    "test.m"      info        auto        "string('...') is not recommended. Use "..." instead."                                          STRQUOT        8           8            1            13        "C:\MyCode\test.m"

In R2023b: The information contained in the a codeIssues object can be exported using export.

Analyze Files Using the Code Issues Panel in MATLAB Online

In MATLAB Online™, you can use the Code Issues panel to view error and warning messages about your code. The Code Issues panel displays the coding problems found by the MATLAB Code Analyzer as it automatically checks your code.

To open the Code Issues panel, go to the Editor or Live Editor tab, and in the Analyze section, click Code Issues. Alternatively, you can open the panel using the Open more panels button () in a sidebar. By default, the Code Issues panel opens on the right side of the desktop. To hide the Code Issues panel, click the Code Issues icon in the sidebar.

Code Issues panel showing 3 errors, 2 warnings, and 11 info messages found in the lengthofline.m file

You can change what messages display in the Code Issues panel using the options at the top of the panel:

Change which files to look for issues in — In the drop-down list at the top-left of the Code Issues panel, select Open Files to show the errors, warnings, and info messages for the current file or Open Files to show the errors, warnings, and info messages for all open files.
Filter messages by type — At the top-right of the Code Issues panel, click the Errors , Warnings , or Infos button to toggle whether to show messages of that type. For example, to show only errors, click the Errors button on and the Warnings and Infos buttons off.
Filter messages by text — Use the search field below the drop-down list to filter the list of messages by text. For example, to display only messages that contain the word Variable, enter the word Variable in the search field.

Adjust Code Analyzer Message Indicators and Messages

You can specify which type of coding issues are underlined to best suit your current development stage. For example, when first coding, you might prefer to underline only errors, because warnings can be distracting. To change the underlining preferences, on the Home tab, in the Environment section, click Preferences. Select MATLAB > Code Analyzer, and then select an Underlining option.

You also can adjust what messages you see when analyzing your code. Code analysis does not provide perfect information about every situation. Sometimes, you might not want to change the code based on a message. If you do not want to change the code, and you do not want to see the indicator and message for a specific line, you can suppress them. For example, the first message on line 48 of the sample file lengthofline.m is Terminate statement with semicolon to suppress output (in functions). Adding a semicolon to the end of a statement suppresses output and is a common practice. Code analysis alerts you to lines that produce output, but lack the terminating semicolon. If you want to view output from line 48, do not add the semicolon as the message suggests.

You can suppress (turn off) the indicators for warning and error messages in these ways:

Suppress an instance of a message in the current file.
Suppress all instances of a message in the current file.
Suppress all instances of a message in all files.

You cannot suppress error messages such as syntax errors.

Suppress an Instance of a Message in the Current File

You can suppress a specific instance of a Code Analyzer message in the current file. For example, to suppress the message on line 48 in the sample file lengthofline.m, right-click the first underline on line 48 and select Suppress 'Terminate statement with semicolon...' > On This Line.

The comment %#ok<NOPRT> appears at the end of the line, which instructs MATLAB to suppress the Terminate statement with semicolon to suppress output (in functions) Code Analyzer message for that line. The underline and mark in the indicator bar for the message disappear.

If a line contains two messages that you do not want to display, right-click each underline separately and select the appropriate entry from the context menu. The %#ok syntax expands. For example, suppressing both messages for line 48 in the sample file lengthofline.m adds the comment %#ok<NBRAK,NOPRT> at the end of the line.

Even if Code Analyzer preferences are set to enable this message, the specific instance of the suppressed message does not appear because the %#ok takes precedence over the preference setting. If you later decide you want to show the Terminate statement with semicolon to suppress output (in functions) Code Analyzer message for that line, delete %#ok<NOPRT> from the line.

Suppress All Instances of a Message in the Current File

You can suppress all instances of a specific Code Analyzer message in the current file. For example, to suppress all instances of the message on line 48 in the sample file lengthofline.m, right-click the first underline on line 48 and select Suppress 'Terminate statement with semicolon...' > In This File.

The comment %#ok<*NOPRT> appears at the end of the line, which instructs MATLAB to suppress all instances of the Terminate statement with semicolon to suppress output (in functions) Code Analyzer message in the current file. All underlines and marks in the message indicator bar that correspond to this message disappear.

If a line contains two messages that you do not want to display anywhere in the current file, right-click each underline separately and select the appropriate entry from the context menu. The %#ok syntax expands. For the example, suppressing both messages for line 48 in the sample file lengthofline.m adds the comment %#ok<*NBRAK,*NOPRT>.

Even if Code Analyzer preferences are set to enable this message, the message does not appear because the %#ok takes precedence over the preference setting. If you later decide you want to show all instances of the Terminate statement with semicolon to suppress output (in functions) Code Analyzer message in the current file, delete %#ok<*NOPRT> from the line.

Suppress All Instances of a Message in All Files

You can disable all instances of a Code Analyzer message in all files. For example, to suppress all instances in all files of the message on line 48 in the sample file lengthofline.m, right-click the first underline on line 48 and select Suppress 'Terminate statement with semicolon...' > In All Files. This option modifies the Code Analyzer preferences.

If you know which messages you want to suppress, you can disable them directly using Code Analyzer preferences:

On the Home tab, in the Environment section, click Preferences.
Select MATLAB > Code Analyzer.
Search the messages to find the ones you want to suppress.
Clear the check box associated with each message you want to suppress in all files.
Click OK.

Save and Reuse Code Analyzer Message Settings

You can set options to enable or disable certain Code Analyzer messages, and then save those settings to a file. When you want to use a settings file with a particular file, you select it from the Code Analyzer preferences. The settings file remains in effect until you select another settings file. Typically, you change the settings file when you have a subset of files for which you want to use a particular settings file.

To save settings to a file:

On the Home tab, in the Environment section, click Preferences.
Select MATLAB > Code Analyzer.
Enable or disable specific messages or categories of messages.
Click the Actions button , select Save As, and then save the settings to a txt file.
Click OK.

You can reuse these settings for any MATLAB file, or provide the settings file to another user. To use the saved settings:

On the Home tab, in the Environment section, click Preferences.
Select MATLAB > Code Analyzer.
Open the Active settings list and select Browse.
Choose from any of your settings files.
The settings you choose remain in effect for all MATLAB files until you select another set of Code Analyzer settings.

Enable custom checks and configure existing checks

Since R2023a

You can configure existing checks displayed in the MATLAB editor by the Code Analyzer and add custom checks by placing a file named codeAnalyzerConfiguration.json in a resources folder. The configuration file is effective in the folder containing the resources folder and any subfolders.

You can modify existing Code Analyzer checks, including whether the check is enabled and its severity, message text, and parameters if the check has any, such as to limit the number of input and output arguments for a function. You can also create custom checks that trigger when specific functions are used. For more information on configuring Code Analyzer checks, see Configure Code Analyzer.

Validate your codeAnalyzerConfiguration.json configuration file for proper formatting by using the function matlab.codeanalysis.validateConfiguration.

Understand Code Containing Suppressed Messages

If you receive code that contains suppressed messages, you might want to review the messages without having to unsuppress them first. A message might be in a suppressed state for any of the following reasons:

One or more %#ok<message-ID> directives are on a line of code that elicits a message specified by <message-ID>.
One or more %#ok<*message-ID> directives are in a file that elicits a message specified by <message-ID>.
The messages are cleared in the Code Analyzer preferences pane.
The messages are disabled by default.

To determine why messages are suppressed call codeIssues with the file as the input.

issues = codeIssues("myFile.m")

The output, issues, will have a property, SuppressedIssues, contains a table listing all the suppressed issues within the file. Review the message associated with each issue to understand why it is suppressed.

Understand the Limitations of Code Analysis

Code analysis is a valuable tool, but it has some limitations:

Code analysis sometimes fails to produce Code Analyzer messages where you expect them.
By design, code analysis attempts to minimize the number of incorrect messages it returns, even if this behavior allows some issues to go undetected.
Code analysis sometimes produces messages that do not apply to your situation.
Clicking the Details button to display additional information for a message can help you determine if the message applies to your situation. Error messages are almost always problems. However, many warnings are suggestions to look at something in the code that is unusual, but might be correct in your case.
Suppress a warning message if you are certain that the message does not apply to your situation. If your reason for suppressing a message is subtle or obscure, include a comment giving the rationale. That way, those who read your code are aware of the situation.
For more information, see Adjust Code Analyzer Message Indicators and Messages.

Distinguish Function Names from Variable Names

Code analysis cannot always distinguish function names from variable names. For the following code, if the Code Analyzer message is enabled, code analysis returns the message, Code Analyzer cannot determine whether xyz is a variable or a function, and assumes it is a function. Code analysis cannot make a determination because xyz has no obvious value assigned to it. However, the code might have placed the value in the workspace in a way that code analysis cannot detect.

function y=foo(x)
   .
   .
   .
   y = xyz(x);
end

For example, in the following code, xyz can be a function or a variable loaded from the MAT-file. Code analysis has no way of making a determination.

function y=foo(x)
    load abc.mat
    y = xyz(x);
end

Variables might also be undetected by code analysis when you use the eval, evalc, evalin, or assignin functions.

If code analysis mistakes a variable for a function, do one of the following:

Initialize the variable so that code analysis does not treat it as a function.
For the load function, specify the variable name explicitly in the load command line. For example:
```
 function y=foo(x)
     load abc.mat xyz
     y = xyz(x);
 end
```

Distinguish Structures from Handle Objects

Code analysis cannot always distinguish structures from handle objects. In the following code, if x is a structure, you might expect a Code Analyzer message indicating that the code never uses the updated value of the structure. If x is a handle object, however, then this code can be correct.

function foo(x)
		x.a = 3;
end

Code analysis cannot determine whether x is a structure or a handle object. To minimize the number of incorrect messages, code analysis returns no message for the previous code, even though it might contain a subtle and serious bug.

Distinguish Built-In Functions from Overloaded Functions

If some built-in functions are overloaded in a class or on the path, Code Analyzer messages might apply to the built-in function, but not to the overloaded function you are calling. In this case, suppress the message on the line where it appears or suppress it for the entire file.

For information on suppressing messages, see Adjust Code Analyzer Message Indicators and Messages.

Determine the Size or Shape of Variables

Code analysis has a limited ability to determine the type of variables and the shape of matrices. Code analysis might produce messages that are appropriate for the most common case, such as for vectors. However, these messages might be inappropriate for less common cases, such as for matrices.

Analyze Class Definitions with Superclasses

Code Analyzer has limited capabilities to check class definitions with superclasses. For example, Code Analyzer cannot always determine if the class is a handle class, but it can sometimes validate custom attributes used in a class if the attributes are inherited from a superclass. When analyzing class definitions, Code Analyzer tries to use information from the superclasses, but often cannot get enough information to make a certain determination.

Analyze Class Methods

Most class methods must contain at least one argument that is an object of the same class as the method. But this argument does not always have to be the first argument. When it is, code analysis can determine that an argument is an object of the class you are defining, and can do various checks. For example, code analysis can check that the property and method names exist and are spelled correctly. However, when code analysis cannot determine that an object is an argument of the class you are defining, then it cannot provide these checks.

Enable MATLAB Compiler Deployment Messages

You can switch between showing or hiding MATLAB Compiler deployment messages when you work on a file by changing the Code Analyzer preference for this message category. Your choice likely depends on whether you are working on a file to be deployed. Changing this preference also changes the setting in the Editor. Similarly, changing the setting in the Editor changes this preference. However, if the Code Analyzer preferences are open when you modify the setting in the Editor, the changes are not reflected in the Preferences window. Whether you change the setting in the Editor or the Preferences window, the change applies to the Editor and the Code Analyzer Report.

To enable MATLAB Compiler™ deployment messages:

On the Home tab, in the Environment section, click Preferences.
Select MATLAB > Code Analyzer.
Click the down arrow next to the search field, and then select Show Messages in Category > MATLAB Compiler (Deployment) Messages.
Click the Enable Category button to the right of the MATLAB Compiler (Deployment) Messages category title.
Clear individual messages that you do not want to display for your code.
Decide if you want to save these settings, so you can reuse them the next time you work on a file to be deployed.

The settings txt file, which you can create as described in Save and Reuse Code Analyzer Message Settings, includes the status of this setting.

External Websites

Programming: Structuring Code (MathWorks Teaching Resources)