Standard Breakpoints

A standard breakpoint pauses at a specific line in a file. To set a standard breakpoint, click the gray area to the left of the executable line where you want to set the breakpoint. Alternatively, you can press the F12 key to set a breakpoint at the current line. If you attempt to set a breakpoint at a line that is not executable, such as a comment or a blank line, MATLAB sets it at the next executable line.

To set a standard breakpoint programmatically, use the dbstop function. For example, to add a breakpoint at line three in a file named plotRand.m, type:

dbstop in plotRand at 3

When debugging a file that contains a loop, set the breakpoint inside the loop to examine the values at each increment of the loop. Otherwise, if you set the breakpoint at the start of the loop, MATLAB pauses at the loop statement only once. For example, this code creates an array of ten ones and uses a for loop to perform a calculation on items two through six of the array:

x = ones(1:10);

for n = 2:6
    x(n) = 2 * x(n-1);
end

Conditional Breakpoints

A conditional breakpoint causes MATLAB to pause at a specific line in a file only when the specified condition is met. For example, you can use conditional breakpoints when you want to examine results after some iterations in a loop.

To set a conditional breakpoint, right-click the gray area to the left of the executable line where you want to set the breakpoint and select Set Conditional Breakpoint. If a breakpoint already exists on that line, select Set/Modify Condition. In the dialog box that opens, enter a condition and click OK. A condition is any valid MATLAB expression that returns a logical scalar value.

When you run the code, MATLAB evaluates the condition before running the line. If the condition is met, MATLAB enters debug mode and pauses at the line. For example, this code creates an array of ten ones and uses a for loop to perform a calculation on items two through six of the array:

x = one(1:10)

for n = 2:6
    x(n) = 2 * x(n-1);
end

Set a conditional breakpoint at line four with the condition n >= 4. When you run the code, MATLAB runs through the for loop twice and pauses on the third iteration at line four when n is 4. If you continue running the code, MATLAB pauses again at line four on the fourth iteration when n is 5, and then once more, when n is 6.

You also can set a conditional breakpoint programmatically using the dbstop function. For example, to add a conditional breakpoint in myprogram.m at line six, type:

dbstop in myprogram at 6 if n>=4

Error Breakpoints

In the Editor, you can set an error breakpoint to have MATLAB pause and enter debug mode if MATLAB encounters an issue. Setting error breakpoints is not supported in the Live Editor.

Unlike standard and conditional breakpoints, you do not set error breakpoints at a specific line or in a specific file. When you set an error breakpoint, MATLAB pauses at any line in any file if the error condition specified occurs. MATLAB then enters debug mode and opens the file containing the error, with the execution arrow at the line containing the error.

To set an error breakpoint, on the Editor tab, click Run and select from these options:

Alternatively, you can set an error breakpoint programmatically by using the dbstop function with a specified condition. For example, to pause execution on all errors, type:

dbstop if error

dbstop if caught error MATLAB:ls:InputsMustBeStrings

Breakpoints in Anonymous Functions

You can set multiple breakpoints in a line of MATLAB code that contains anonymous functions. You can set a breakpoint for the line itself and for each anonymous function in the line.

To set a breakpoint on a line containing an anonymous function, click the gray area to the left of the line. MATLAB adds a breakpoint for the line, and a disabled breakpoint for each anonymous function in the line. To enable a breakpoint for an anonymous function, click the disabled breakpoint for that function.

To view information about all the breakpoints on a line, place your cursor on the breakpoint icon. A tooltip appears with available information. For example, in this code, line seven contains two anonymous functions, with a breakpoint at each one.

When you set a breakpoint in an anonymous function, MATLAB pauses when the anonymous function is called. The line highlighted in green is where the code defines the anonymous function. The line highlighted in gray is where the code calls the anonymous functions. For example, in this code, MATLAB pauses the program at a breakpoint set for the anonymous function g, defined at line seven, and called at line eight.

Invalid Breakpoints

A dark gray breakpoint indicates an invalid breakpoint.

Breakpoints are invalid for these reasons:

Disable Breakpoints

You can disable selected breakpoints so that your program temporarily ignores them and runs uninterrupted. For example, you might disable a breakpoint after you think you identified and corrected an issue or if you are using conditional breakpoints.

To disable a breakpoint, right-click the breakpoint icon, and select Disable Breakpoint from the context menu.

The breakpoint becomes light gray to indicate that it is disabled.

To reenable a breakpoint, right-click the breakpoint icon and select Enable Breakpoint from the context menu.

The gray breakpoints become red, and program execution pauses at that line.

To enable or disable all breakpoints in the file, right-click the gray area to the left of an executable line and select Enable All Breakpoints in File or Disable All Breakpoints in File. These options are available only if there is at least one breakpoint to enable or disable.

Clear Breakpoints

All breakpoints remain in a file until you clear (remove) them or until they are cleared automatically at the end of your MATLAB session.

To clear a breakpoint, right-click the breakpoint icon and select Clear Breakpoint from the context menu. Alternatively, you can press the F12 key to clear the breakpoint.

To clear a breakpoint programmatically, use the dbclear function. For example, to clear the breakpoint at line six in a file called myprogram.m, type:

 dbclear in myprogram at 6

To clear all breakpoints in the file, right-click the breakpoint alley and select Clear All Breakpoints in File. You can also use the dbclear all command. For example, to clear all the breakpoints in a file called myprogram.m, type:

dbclear all in myprogram

To clear all breakpoints in all files, including error breakpoints, right-click the breakpoint alley and select Clear All Breakpoints. You also can use the dbclear all command.

Breakpoints clear automatically when you end a MATLAB session. To save your breakpoints for future sessions, use the dbstatus function.