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At this point, we know there is a bug and it s reproducible, meaning that we can use VS to debug and find the cause of the problem In this situation, the program is saying that it didn t find a Customer record or, in other words, there is no record with a FirstName of Jean However, we know for a fact that the data does include a customer whose FirstName is Jean We need to find out why the program cannot find it The following steps show how the VS debugger can help isolate the problem
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1 Start by setting a breakpoint on the foreach loop in the Main method This wasn t an
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arbitrary decision Instead, considering the nature of the problem, I selected a part of the program that is likely to begin providing a cue to what the problem is Looking at the program, one of the reasons that the program might not find the searchName is that we aren t getting data, causing the program to not execute the body of the foreach loop
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2 Press F5 to run the program in debug mode This will execute the program and make it
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stop on the foreach loop, making it possible to look at program state
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3 After VS hits the breakpoint, hover over customers to see if there are any values
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You ll observe that customers does have three values The fact that there are customers indicates that the foreach loop is executing and we ve eliminated that as a possibility
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4 Next, set a breakpoint on the if statement, right-click the breakpoint, and set the
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condition as follows: C#:
custFirstName == "Jean"
custFirstName = "Jean"
The goal here is to see what happens when the if statement finds the record matching the searchName At this point, we re assuming that Jean does exist in the data Working with a small program, you can use windows such as Autos, Locals, or Watch to find this record However, many real-world scenarios will give you a list with many more records Therefore, rather than waste time drilling down through dozens of records, use the VS debugger to help find the record quickly Keep in mind that all the best plans don t always work out, as you ll soon see, but the primary point is taking the most productive step first Setting a conditional breakpoint demonstrates how you can set conditions that can avoid eating up time caused by stepping through loops
5 Press F5 to run the program You expect to hit the breakpoint, but that won t happen
Confusing We know that there isn t anything wrong with the logic, because the if statement condition is a simple equality operator Perhaps we ve looked in the database or whatever source the data came from, but it s given in this scenario that Jean is definitely in the data However, this illustrates a common problem where the quality of data you work with is less than desired
6 This time, change the breakpoint condition on the if statement as follows and re-run the
program: C#:
custFirstNameContains("Jean")
custFirstNameContains("Jean")
Remember, we suspect bad data, so the call to Contains on the string assumes that there might be some extraneous white space or other characters around the name in the data Hover over custFirstName or look at cust in one of the debug windows to verify it is the record you are looking for This breakpoint will pause on any records that contain the sequence of characters Jean , such as Jean-Claude So, you might have multiple matches that aren t what you want The benefit is that the number of records you must
6: Debugging with Visual Studio
look at is much fewer and you can save time If you have multiple records, you can press F5 and the breakpoint will pause on each record, allowing you to inspect the value In this case, the record set is so small that we hit the right record immediately
7 Press F10 to step over the if condition This will tell us whether the condition is being
evaluated properly In this case, VS does not step into the if statement but instead moves to the end of the if statement, meaning that searchName and custFirstName are not equal This means you need to take a closer look at custFirstName to see what the problem is with the data
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