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Using the Watch Window

While you are busy stepping through your code, you can watch the values of your Watch expressions in the Watch window. For instance, consider a loop such as this:

Dim i as Integer, j as Integer, k as Integer
Dim astrAlphabet(0 to 25) as String
j = LBound(astrAlphabet)
k = UBound(astrAlphabet)
For i = j to k
astrAlphabet (i) = Chr$( i + 65)
Next

This loop populates a 26-element array with the letters of the alphabet. If you set a breakpoint and create a watch on the astrAlphabet array, you can watch the values of each element of the array as they are assigned values in the loop. However, you won’t see the array build a string such as "ABCDEFGHIJKLMNOPQRSTUVWXYZ". In fact, if you only watch the single line containing the name of the array, you won’t see much of anything useful except for the range of the array index values (in this case, 0 to 25). That’s because an array is a data structure that contains more than one value, and each line in the Watch window can only display an individual value.

Watching Arrays

Don’t worry. You don’t need to set a separate watch for each element of the array. When dealing with a data structure such as an array, the Watch window will display the name of the array with a boxed plus sign next to it, as shown in Figure 18.9. It works in the same way that Windows Explorer displays a disk drive’s directory structure in a tree control. Just as Windows Explorer uses plus signs to indicate that nested subdirectories remain to be displayed, the VB Watch window uses plus signs to indicate that more data elements are nested within the selected structure.

When a watch is set on an array, you will see a boxed plus sign next to it.
FIGURE 18.9. When a watch is set on an array, you will see a boxed plus sign next to it.

If you click the plus sign, the structure unfolds to display each individual data element, as shown in Figure 18.10. The plus sign changes to a minus sign, which you can click on to hide the elements contained in the structure again.

Click on the plus sign to monitor the values of the elements contained in the array.
FIGURE 18.10. Click on the plus sign to monitor the values of the elements contained in the array.

Watching User-Defined Types

The same nesting principle applies to user-defined types. If you create a type to store an employee’s name, ID number, and Social Security number, it might look like this:

Type tEmployee
strName as String
iIDNumber as Integer
lSocSecNum as Long
End Type

If you create a variable of type tEmployee, and then set a watch on that variable, the Watch window will display the name of your variable and a plus sign. As with the array, you need to click on the plus sign to unfold the strName, iIDNumber, and lSocSecNum elements of the data structure.

It is also possible to have multiple levels of nested structures in the Watch window. If you were to create an array of tEmployee variables called atMyEmployees, for example, you would need to click on the plus sign associated with the atMyEmployees array to display the tEmployee elements. To see the values contained for each tEmployee, you would in turn have to click on the plus sign associated with each element in the array.


  

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