{"id":5717,"date":"2022-09-29T16:22:56","date_gmt":"2022-09-29T20:22:56","guid":{"rendered":"https:\/\/blogs.mathworks.com\/steve\/?p=5717"},"modified":"2022-09-30T11:07:17","modified_gmt":"2022-09-30T15:07:17","slug":"code-trace-for-matlab","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/steve\/2022\/09\/29\/code-trace-for-matlab\/","title":{"rendered":"Code Trace for MATLAB"},"content":{"rendered":"
Today's post departs from image processing, my usual subject. Instead, I want to tell you about something that I just put up on <\/span>GitHub<\/span><\/a> and the <\/span>MATLAB File Exchange<\/span><\/a>.<\/span><\/div>
Earlier this year, I was debugging some code, and I wanted to know what was happening inside a certain function <\/span>while the function was running<\/span>. Typically, the way to do this is to modify the code by adding something like a call to disp:<\/span><\/div>
disp(<\/span>\"Made it to this line, and the value of n is \" <\/span>+ n)<\/span><\/span><\/div><\/div>
But modifying the code is often undesirable. You have to remember to restore the code to its original state when you are done, and you might be working with code that is stored in a read-only location.<\/span><\/div>
So, I started tinkering with ways to achieve a similar effect while leaving the code untouched, and I hit on the notion of using conditional breakpoints. When you set a conditional breakpoint on a code line in a file, then code execution stops at that line if an expression that you specify evaluates to <\/span>true<\/span> (1). Here is a screenshot of setting a conditional breakpoint using the MATLAB Editor. Here, I'm creating a breakpoint that will stop execution at line 2 of fib.m if the value of <\/span>n<\/span> is 4.<\/span><\/div>
\"conditional-breakpoint-screenshot.png\"<\/img><\/div>
Well, we can use this to replace our use of <\/span>disp<\/span> if we can create an expression that:<\/span><\/div>