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| R2012a Documentation → MATLAB | |
Learn more about MATLAB |
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Correct Problems and End Debugging Breakpoints in Anonymous Functions |
You can debug MATLAB files using the Editor, which is a graphical user interface, as well as by using debugging functions from the Command Window. You can use both methods interchangeably. These topics and the example describe both methods.
Do the following to prepare for debugging:
Open the file — To use the Editor for debugging, open it with the file to run.
Save changes — If you are editing the file, save the changes before you begin debugging. If you try to run a file with unsaved changes from within the Editor, the file is automatically saved before it runs. If you run a file with unsaved changes from the Command Window, MATLAB software runs the saved version of the file. Therefore, you do not see the results of your changes.
Add the files to a folder on the search path or put them in the current folder. Be sure the file you run and any files it calls are in folders that are on the search path. If all required files are in the same folder, you can instead make that folder the current folder.
The debugging process and features are best described using an example. To prepare to use the example, create two files, collatz.m and collatzplot.m, that produce data for the Collatz problem.
For any given positive integer, n, the Collatz function produces a sequence of numbers that always resolves to 1. If n is even, divide it by 2 to get the next integer in the sequence. If n is odd, multiply it by 3 and add 1 to get the next integer in the sequence. Repeat the steps until the next integer is 1. The number of integers in the sequence varies, depending on the starting value, n.
The Collatz problem is to prove that the collatz function resolves to 1 for all positive integers. The files for this example are useful for studying the Collatz problem. The file collatz.m generates the sequence of integers for any given n. The file collatzplot.m calculates the number of integers in the sequence for all integers from 1 through m, and plots the results. The plot shows patterns that you can study further.
Following are the results when n is 1, 2, or 3.
n | Sequence | Number of Integers in the Sequence |
|---|---|---|
1 | 1 | 1 |
2 | 2 1 | 2 |
3 | 3 10 5 16 8 4 2 1 | 8 |
Files for the Collatz Problem. Following are the two files you use for the debugging example. To create these files on your system, open two new files. Select and copy the following code from the Help browser and paste it into the files. Save and name the files collatz.m and collatzplot.m. Save them to your current folder or add the folder where you save them to the search path. One of the files has an embedded error to illustrate the debugging features.
Open the files by issuing the following commands, and then saving each file to a local folder:
open(fullfile(matlabroot,'help','techdoc','matlab_env',... 'examples','collatz.m'))
open(fullfile(matlabroot,'help','techdoc','matlab_env',... 'examples','collatzplot.m'))
Trial Run for the Example. Open the file collatzplot.m. Make sure that the current folder is the folder in which you saved collatzplot.
Try out collatzplot to see if it works correctly. Use a simple input value, for example, 3, and compare the results to those shown in the preceding table. Typing
collatzplot(3)
produces the plot shown in the following figure.
The plot for n = 1 appears to be correct—for 1, the Collatz series is 1, and contains one integer. But for n = 2 and n = 3, it is wrong. There should be only one value plotted for each integer, the number of integers in the sequence, which the preceding table shows to be 2 (for n = 2) and 8 (for n = 3). Instead, multiple values are plotted. Use MATLAB debugging features to isolate the problem.
Set breakpoints to pause execution of the MATLAB file so you can examine values where you think the problem can be. You can the Editor, using functions in the Command Window, or both.
There are three basic types of breakpoints you can set in MATLAB files:
A standard breakpoint, which stops at a specified line in a file. For details, see Set Standard Breakpoints.
A conditional breakpoint, which stops at a specified line in a file only under specified conditions. For details, see Conditional Breakpoints.
An error breakpoint that stops in any file when it produces the specified type of warning, error, or NaN or infinite value. For details, see Error Breakpoints.
You can disable standard and conditional breakpoints so that MATLAB temporarily ignores them, or you can remove them. For details, see Disable and Clear Breakpoints. Breakpoints do not persist after you exit the MATLAB session.
You can only set valid standard and conditional breakpoints at executable lines in saved files that are in the current folder or in folders on the search path. When you add or remove a breakpoint in a file that is not in a folder on the search path or in the current folder, a dialog box appears. This dialog box presents options that allow you to add or remove the breakpoint. You can either change the current folder to the folder containing the file, or you can add the folder containing the file to the search path.
Do not set a breakpoint at a for statement if you want to examine values at increments in the loop. For example, in
for n = 1:10
m = n+1;
end MATLAB executes the for statement only once, which is efficient. Therefore, when you set a breakpoint at the for statement and step through the file, you only stop at the for statement once. Instead place the breakpoint at the next line, m=n+1 to stop at each pass through the loop.
You cannot set breakpoints while MATLAB is busy, for example, running a file, unless that file is paused at a breakpoint.
To set a standard breakpoint using the Editor:
If you have changed the file, save it.
Click in the breakpoint alley at an executable line where you want to set the breakpoint.
The breakpoint alley is the narrow column on the left side of the Editor, to the right of the line number.
Executable lines are preceded by a - (dash).
If you attempt to set breakpoints at lines that are not executable, such as comments or blank lines, MATLAB sets it at the next executable line.
Other ways to set a breakpoint are to:
Position the cursor in an executable line and then
click the Set/clear breakpoint button
on the toolbar.
From the Debug menu, select Set/Clear Breakpoint.
Set Breakpoints for the Example. It is unclear whether the problem in the example is in collatzplot or collatz. To start, follow these steps:
In collatzplot.m, click the dash in the breakpoint alley at line 9 to set a breakpoint.
This breakpoint enables you to step into collatz to see if the problem is there.
Set additional breakpoints at lines 10 and 11.
These breakpoints stop the program so you can examine the interim results.
Valid (Red) and Invalid (Gray) Breakpoints. Red breakpoints indicate valid standard breakpoints.
Breakpoints are gray for either of these reasons:
There are unsaved changes in the file. Save the file to make breakpoints valid. The gray breakpoints become red, indicating they are now valid. Any gray breakpoints that you entered at invalid breakpoint lines automatically move to the next valid breakpoint line with a successful file save.
There is a syntax error in the file. When you set a breakpoint, an error message appears indicating where the syntax error is. Fix the syntax error and save the file to make breakpoints valid.
The following image shows three invalid breakpoints at lines 9, 10, and 11. Notice the asterisk next to the file name in the title bar. It indicates the file has unsaved changes.
To set a breakpoint using the debugging functions, use dbstop. For the example, type:
dbstop in collatzplot at 9 dbstop in collatzplot at 10 dbstop in collatzplot at 11
After setting breakpoints, run the file from the Command Window or the Editor.
For the example, run collatzplot for the simple input value, 3, by typing the following in the Command Window:
collatzplot(3)
The example, collatzplot, requires an input argument and therefore runs only from the Command Window or from a run configuration with a value specified.
Running the file results in the following:
The prompt in the Command Window changes to
K>>
indicating that MATLAB is in debug mode.
The program pauses at the first breakpoint. This means that line will be executed when you continue. The pause is indicated in the Editor by the green arrow just to the right of the breakpoint. In the example, the pause is at line 9 of collatzplot, as shown here:
The line at which you are paused displays in the Command Window. For the example:
The function the Stack field displays on the toolbar changes to reflect the current function (sometimes referred to as the caller or calling workspace). The call stack includes subfunctions as well as called functions. If you use debugging functions from the Command Window, use dbstack to view the current call stack.
If the file you are running is not in the current folder or a folder on the search path, you are prompted to either add the folder to the path or change the current folder.
In debug mode, you can set breakpoints, step through programs, examine variables, and run other functions.
MATLAB software could become nonresponsive if it stops at a breakpoint while displaying a modal dialog box or figure that your file creates. In that event, press Ctrl+C to go the MATLAB prompt.
While debugging, you can step through a MATLAB file, pausing at points where you want to examine values.
Use any of the following methods:
The Editor toolbar buttons
If the toolbar is not displaying, right-click the Editor menu bar, and then select Editor Toolbar.
Step options in the Editor Debug menu
Details about these methods appear in the following table.
Toolbar Button | Debug Menu Item | Description | Function Alternative |
|---|---|---|---|
 | Run file or Run Configuration for file | Commence execution of file and run until completion or until a breakpoint is encountered. The Run Configurations for file menu option provides a submenu. The submenu enables you to select a particular run configuration or to edit the run configurations for the MATLAB file. If you choose Run file, MATLAB uses the default run configuration. | None |
None | Go Until Cursor | Continue execution of file until the line where the cursor is positioned. Also available on the context menu. | None |
 | Step | Execute the current line of the file. | |
 | Step In | Execute the current line of the file and, if the line is a call to another function, step into that function. | dbstep in |
| Continue | Resume execution of file until completion or until another breakpoint is encountered. | |
 | Step Out | After stepping in, run the rest of the called function or subfunction, leave the called function, and pause. | dbstep out |
 | Exit Debug Mode | Exit debug mode. | dbquit out |
In the example, collatzplot is paused at
line 9. Because the problem results are correct for N/n =
1, continue running until N/n = 2. Press the Continue
button
three times to move through the breakpoints
at lines 9, 10, and 11. Now the program is again paused at the breakpoint
at line 9.
Now that collatzplot is paused at line 9
during the second iteration, use the Step In button
or type dbstep
in in the Command Window to step into collatz and
walk through that file. Stepping into line 9 of collatzplot goes
to line 9 of collatz. If collatz is
not open in the Editor, it automatically opens if you have selected Debug > Open Files When Debugging.
The pause indicator at line 9 of collatzplot changes
to a hollow arrow
, indicating that MATLAB control
is now in a subfunction called from the main program. The call stack
shows that the current function is now collatz.
In the called function, collatz in the example, you can do the same things you can do in the main (calling) function—set breakpoints, run, step through, and examine values.
While the program is paused, you can view the value of any variable currently in the workspace. Examine values when you want to see whether a line of code has produced the expected result or not. If the result is as expected, continue running or step to the next line. If the result is not as you expect, then that line, or a previous line, contains an error. Use the following methods to examine values:
Many of these methods are used in Examine Values in the Example.
Variables assigned through the Command Window and created using scripts are considered to be in the base workspace. Variables created in a function belong to their own function workspace. To examine a variable, you must first select its workspace. When you run a program, the current workspace is shown in the Stack field. To examine values that are part of another workspace for a currently running function or for the base workspace, first select that workspace from the list in the Stack field.
If you use debugging functions from the Command Window:
To display the call stack, use dbstack.
To list the variables in the current workspace, use who or whos.
Workspace in the Example. At line 9 of collatzplot, you stepped in, and the current line is 9 in collatz. The Stack field shows that collatz is the current workspace.
To view the current value of a variable in the Editor, first enable datatips, then use the mouse to display a datatip:
Select File > Preferences > Editor/Debugger > Display.
Select Enable datatips in edit mode.
In the Editor, position the mouse pointer to the left of a variable.
The variable's current value appears in a data tip. The data tip stays in view until you move the pointer. If you have trouble getting the data tip to appear, click in the line containing the variable, and then move the pointer next to the variable.
You can examine values while in debug mode at the K>> prompt. To see the variables currently in the workspace, use who. Type a variable name in the Command Window and it displays the variable's current value. For the example, to see the value of n, type
n
The Command Window displays the expected result
n = 2
and displays the debug prompt, K>>.
You can view the value of variables in the Value column of the Workspace browser. The Workspace browser displays all variables in the current workspace. Use Stack in the Workspace browser to change to another workspace and view its variables.
The Value column does not show all details for all variables. To see details, double-click a variable in the Workspace browser. The Variable Editor opens, displaying the content for that variable. You can open the Variable Editor directly for a variable using openvar.
To see the value of n in the Variable Editor for the example, type
openvar n
and the Variable Editor opens, showing that n = 2 as expected.
Select a variable or equation in a MATLAB file in the Editor. Right-click and select Evaluate Selection from the context menu (for a single-button mouse, press Ctrl+click). The Command Window displays the value of the variable or equation. You cannot evaluate a selection while MATLAB is busy, for example, running a file.
Step from line 9 through line 13 in collatz. Step again, and the pause indicator jumps to line 17, just after the if loop, as expected. Step again, to line 18, check the value of sequence in line 17 and see that the array is
2 1
as expected for n = 2. Step again, which
moves the pause indicator from line 18 to line 11. At line 11, step
again. Because next_value is now 1, the while loop
ends. The pause indicator is at line 11 and appears as a green down
arrow
. This indicates that processing in
the called function is complete and program control will return to
the calling program. Step again from line 11 in collatz and
execution is now paused at line 9 in collatzplot.
Note that instead of stepping through collatz, the called function, as was just done in this example, you can step out from a called function back to the calling function, which automatically runs the rest of the called function and returns to the next line in the calling function. To step out, use the Step Out button or type dbstep out in the Command Window.
In collatzplot, step again to advance to line 10, and then to line 11. The variable seq_length in line 10 is a vector with the elements:
1 2
which is correct.
Finally, step again to advance to line 12. Examining the values in line 11, N = 2 as expected, but the second variable, plot_seq, has two values, where only one value is expected. While the value for plot_seq is as expected:
2 1
it is the incorrect variable for plotting. Instead, seq_length(N) should be plotted.
Sometimes, if you set a breakpoint in a function, and then attempt to view the value of a variable in the parent workspace using the dbup command, the value of the variable is currently under construction. Therefore, the value is not available. This is true whether you view the value by specifying the dbup command in the Command Window or by using the Stack field on the Editor toolbar.
In such cases, MATLAB returns the following message, where x is the variable for which you are trying to examine the value:
K>> x ??? Reference to a called function result under construction x.
For example, suppose you have code such as the following:
x = collatz(x);
MATLAB detects that the evaluation of collatz(x) replaces the input variable, x. To optimize memory use, MATLAB overwrites the memory that x currently occupies to hold a new value for x. When you request the value of x, and it is under construction, its value is not available, and MATLAB displays the error message.
The following are some of the ways to correct problems and end the debugging session:
Complete the Example uses many of these features.
While debugging, you can change the value of a variable in the current workspace to see if the new value produces expected results. While the program is paused, assign a new value to the variable in the Command Window, Workspace browser, or Variable Editor. Then continue running or stepping through the program. If the new value does not produce the expected results, the program has a different problem.
After identifying a problem, end the debugging session. You must end a debugging session if you want to change and save a file to correct a problem, or if you want to run other functions in MATLAB.
Note Quit debug mode before editing a file. If you edit a file while in debug mode, you can get unexpected results when you run the file. If you do edit a file while in debug mode, breakpoints turn gray, indicating that results might not be reliable. See Valid (Red) and Invalid (Gray) Breakpoints for details. If you attempt to save an edited file while in debug mode, a dialog box opens allowing you to exit debug mode and save the file. |
To end debugging, click the Exit debug mode button
, or select Exit
Debug Mode from the Debug menu.
You can instead use the function dbquit or the Shift+F5 keyboard shortcut to end debugging.
After quitting debugging, pause indicators in the Editor display no longer appear, and the normal prompt >> appears in the Command Window instead of the debugging prompt, K>>. You can no longer access the call stack.
Disable a breakpoint to ignore it temporarily. Clear a breakpoint to remove it.
Disable and Enable Breakpoints. You can disable selected breakpoints so the program temporarily ignores them and runs uninterrupted, for example, after you think you identified and corrected a problem. This is especially useful for conditional breakpoints—see Conditional Breakpoints.
To disable a breakpoint, do one of the following:
Right-click the breakpoint icon and select Disable Breakpoint from the context menu.
Click anywhere in a line and select Enable/Disable Breakpoint from the Debug menu.
To disable a conditional breakpoint, use either of the methods in the preceding list or click the conditional breakpoint icon. An X appears through the breakpoint icon as shown here.
When you run dbstatus, the resulting message for a disabled breakpoint is
Breakpoint on line 9 has conditional expression 'false'.
After disabling a breakpoint, you can reenable it to make it active again or you can clear it.
To reenable a breakpoint, do either of the following:
Right-click the breakpoint icon and select Enable Breakpoint from the context menu.
Click anywhere in a line and select Enable/Disable Breakpoint from the Debug menu.
The X no longer appears on the breakpoint icon and program execution will pause at that line.
Clear (Remove) Breakpoints. All breakpoints remain in a file until you clear (remove) them or until they are cleared automatically. Clear a breakpoint after determining that a line of code is not causing a problem.
To clear a breakpoint in the Editor:
Click anywhere in a line that has a breakpoint and select Set/Clear Breakpoint from the Debug menu.
Click a standard breakpoint icon, or a disabled conditional breakpoint icon.
Use the dbclear in file at lineno command in the Command Window. For the example, clear the breakpoint at line 9 in collatzplot by typing:
dbclear in collatzplot at 9
To clear all breakpoints in all files:
Select Debug > Clear Breakpoints in All Files on the toolbar.
Click the Clear breakpoints in all files button
.
Use dbclear all in the Command Window.
For the example, clear all of the breakpoints in collatzplot by typing:
dbclear all in collatzplot
Breakpoints clear automatically when you:
End the MATLAB session.
Clear the file using clear name or clear all.
Note When clear name or clear all is in a statement in a file that you are debugging, it clears the breakpoints. |
You can use the s=dbstatus syntax and then save s to save the current breakpoints to a MAT-file. At a later time, you can load s and restore the breakpoints using dbstop(s). For more information, including an example, see the dbstatus reference page.
To correct a problem in a MATLAB file:
Do not modify a file while MATLAB is in debug mode. If you do, breakpoints turn gray, indicating that results might not be reliable. See Valid (Red) and Invalid (Gray) Breakpoints for details.
Run the file again to be sure that it produces the expected results.
To correct the problem in the example:
End the debugging session. One way to do this is to select Exit Debug Mode from the Debug menu.
In collatzplot.m line 11, change the string plot_seq to seq_length(N) and save the file.
Clear the breakpoints in collatzplot.m. One way to do this is by typing
dbclear all in collatzplot
in the Command Window.
Run collatzplot for m = 3 by typing
collatzplot(3)
in the Command Window.
Verify the result. The figure shows that the length of the Collatz series is 1 when n = 1, 2 when n = 2, and 8 when n = 3, as expected.
Test the function for a slightly larger value of m, such as 6, to be sure that the results are still accurate. To make it easier to verify collatzplot for m = 6 as well as the results for collatz, add this line at the end of collatz.m
sequence
which displays the series in the Command Window. The results for when n = 6 are
sequence =
6 3 10 5 16 8 4 2 1Then run collatzplot for m = 6 by typing
collatzplot(6)
To make debugging easier, you ran collatzplot for a small value of m. Now that you know it works correctly, run collatzplot for a larger value to produce more interesting results. Before doing so, you consider disabling output for the line you just added in step 6, line 19 of collatz.m, by adding a semicolon to the end of the line so it appears as
sequence;
Then run
collatzplot(500)
The following figure shows the lengths of the Collatz series for n = 1 through n = 500.
It is a good practice to modify a MATLAB file after you quit debugging, and then save the modification and run the file. Otherwise, you might get unexpected results. However, there are situations where you want to experiment during debugging. Perhaps you want to modify a part of the file that has not yet run, and then run the remainder of the file without saving the change. Follow these steps:
While stopped at a breakpoint, modify a part of the file that has not yet run.
Breakpoints turn gray, indicating they are invalid.
Select all of the code after the breakpoint, right-click, and then select Evaluate Selection from the context menu.
You can also use cell mode to do this.
Set conditional breakpoints to cause MATLAB to stop at a specified line in a file only when the specified condition is met. One particularly good use for conditional breakpoints is when you want to examine results after a certain number of iterations in a loop. For example, set a breakpoint at line 10 in collatzplot, specifying that MATLAB stop only if N is greater than or equal to 2. This section covers the following topics:
To set a conditional breakpoint:
Click in the line where you want to set the conditional breakpoint.
From the Debug menu, select Set/Modify Conditional Breakpoint. If a standard breakpoint exists at that line, use this same method to make it conditional.
The MATLAB Editor conditional breakpoint dialog box opens.
Type a condition in the dialog box, where a condition is any valid MATLAB expression that returns a logical scalar value. Click OK. As noted in the dialog box, the condition is evaluated before running the line. For the example, at line 9 in collatzplot, enter the following as the condition:
N>=2
A yellow breakpoint icon (indicating the breakpoint is conditional) appears in the breakpoint alley at that line.
When you run the file, MATLAB software enters debug mode and pauses at the line only when the condition is met. In the collatzplot example, MATLAB runs through the for loop once and pauses on the second iteration at line 9 when N is 2. If you continue executing, MATLAB pauses again at line 9 on the third iteration when N is 3.
The following table describes how to adjust conditional breakpoints.
| To | Do This |
|---|---|
| Modify a condition for a breakpoint in the current line. | Right-click the conditional breakpoint icon, and then from the context menu, select Set/Modify Condition. |
| Disable a conditional breakpoint. | Click the associated conditional breakpoint icon. |
| Clear a conditional breakpoint. | Double-click the associated conditional breakpoint icon. |
The following table lists the functions available for adjusting conditional breakpoints from the Command Window.
| To | Use This Function |
|---|---|
| Set a conditional breakpoint. | dbstop |
| Clear a conditional breakpoint. | dbclear |
| View a list of currently set breakpoints, including the conditional expression for each conditional breakpoint. | dbstatus |
You can set multiple breakpoints in a line of MATLAB code that contains anonymous functions. You can do both of the following:
Set a breakpoint for the line itself (MATLAB software pauses at the start of the line).
Set a breakpoint for each anonymous function in that line.
When you add a breakpoint to a line containing an anonymous
function, the Editor asks where in the line you want to add the breakpoint.
If there is more than one breakpoint in a line, the breakpoint icon
is blue
, regardless of the status of any of
the breakpoints on the line.
To display information in a tooltip about all breakpoints on a line, position the pointer on the blue icon.
To perform a breakpoint action for a line that can contain multiple breakpoints, such as Clear Breakpoint, right-click the breakpoint alley at that line, and then select the action.
When you set a breakpoint in an anonymous function, MATLAB pauses when the anonymous function is called.
The following illustration shows the Editor when you set a breakpoint in the anonymous function sqr in line 2, and then run the file. When you run the file, MATLAB pauses each time that the anonymous function sqr executes. The green arrow shows where the code defines sqr. The white arrow, on line 5, indicates where the code calls sqr.
MATLAB functions often call other MATLAB functions and methods to perform their operations. If you set a breakpoint in a class method, and then run a MATLAB function that results in calling that method, execution stops at the breakpoint. This behavior can be confusing if you are unaware that the MATLAB function calls the method containing the breakpoint.
For instance, suppose you do the following:
Define a class named MyClass that overloads the MATLAB size function.
Create an instance of MyClass.
Insert breakpoints within the MyClass size method.
Call whos.
When you call the whos function, it calls the size function to obtain size information about the variables in the workspace. Under the preceding circumstances, because MyClass overloads the size function, whos calls the MyClass size method instead of the default size function to determine the size of the MyClass object. Execution stops at the breakpoint you set in the size method. You can enable the MATLAB function to execute to completion by either stepping or continuing through the method. To prevent this behavior from recurring, remove the breakpoints.
Set error breakpoints to stop program execution and enter debug mode when MATLAB encounters a problem. Unlike standard and conditional breakpoints, you do not set these breakpoints at a specific line in a specific file. Rather, once set, MATLAB stops at any line in any file when the error condition specified by using the error breakpoint occurs. MATLAB then enters debug mode and opens the file containing the error, with the pause indicator at the line containing the error. Files open only when you select Debug > Open Files when Debugging. Error breakpoints remain in effect until you clear them or until you end the MATLAB session. You can set error breakpoints from the Debug menu in any desktop tool. This section covers the following topics:
To set error breakpoints:
Select Debug > Stop if Errors/Warnings.
In the Stop if Errors/Warnings for All Files dialog box, specify error breakpoints on all appropriate tabs, and then click OK.
To clear error breakpoints, select the Never stop if ... option for all appropriate tabs, and then click OK.
As the tabs in the Stop if Errors/Warnings for All Files dialog box suggest, there are four basic types of error breakpoints you can set:
Errors
When an error occurs, execution stops, unless the error is in a try...catch block. MATLAB enters debug mode and opens the file to the line in the try portion of the block that produced the error. You cannot resume execution.
Try/Catch Errors
When an error occurs in a try...catch block, execution pauses. MATLAB enters debug mode and opens the file to the line that produced the error. You can resume execution or use debugging features.
Warnings
When a warning occurs, MATLAB pauses, enters debug mode, and opens the file, paused at the line that produced the warning. You can resume execution or use debugging features.
NaN or Inf
When an operator, function call, or scalar assignment produces a NaN (not-a-number) or Inf (infinite) value, MATLAB pauses, enters debug mode, and opens the file. MATLAB pauses immediately after the line that encountered the value. You can resume execution or use debugging features.
Select options for these error breakpoints:
Click Never stop if error... on a tab to clear that type of breakpoint.
Click Always stop if error... on a tab to set that type of breakpoint.
Select Use message identifiers... on a tab to limit each type of error breakpoint (except NaN or Inf). Execution stops only for the error you specify by the corresponding message identifier.
This option is not available for the NaN or Inf type of error breakpoint. You can add multiple message identifiers, and edit or remove them.
Pausing Executing for Warnings. To pause execution when MATLAB produces a warning:
Click the Warnings tab.
Click Always stop if warning, and then click OK.
Now, when you run a file and MATLAB produces a warning, execution pauses and MATLAB enters debug mode. The file opens in the Editor at the line that produced the warning.
Set Breakpoints for a Specific Error. To stop execution for a specific error add a message identifier:
In the resulting Add Message Identifier dialog box, type the message identifier of the error for which you want to stop. The identifier is of the form component:message (for example, MATLAB:narginchk:notEnoughInputs). Then click OK.
The message identifier you specified appears in the Stop if Errors/Warnings for All Files dialog box.
Obtain Error Message Identifiers. To obtain an error message identifier generated by a MATLAB function, run the function to produce the error, and then call MExeption.last. For example:
surf MException.last
The Command Window displays the MException object, including the error message identifier in the identifier field. For this example, it displays:
ans =
MException
Properties:
identifier: 'MATLAB:nargchk:notEnoughInputs'
message: 'Not enough input arguments.'
cause: {}
stack: [1x1 struct]
Methods
Obtain Warning Message Identifiers. To obtain a warning message identifier generated by a MATLAB function, run the function to produce the warning. Then, run:
[m,id] = lastwarn
MATLAB returns the last warning identifier to id. An example of a warning message identifier is MATLAB:concatenation:integerInteraction.
The function equivalent for each option in the Stop if Errors/Warnings for All Files dialog box, appears to the right of each option. For example, the function equivalent for Always stop if error is dbstop if error. Use these functions in the Command Window as listed in the following table.
| To | Use This Function |
|---|---|
| Set error breakpoints. | dbstop |
| Clear error breakpoints. | dbclear |
| View a list of currently set breakpoints, including the condition and message identifier for each error breakpoint. | dbstatus |
 | Avoid Mistakes While Editing Code | Debugging Functions |  |
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