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.

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.

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.

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.

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.

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.

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:

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.

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

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:

You cannot suppress error messages such as syntax errors.

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:

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:

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

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

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

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:

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