LabWindows/CVI Tip: Visualizing Data Through LabWindows/CVI Debugging Tools

[Johannes_T]

Summary

Debugging data in complex applications can be challenging, but this tip shows three ways you can conveniently find debugging data when tracking down an error in your code.

Contents

1. Evaluating Compound Expressions Using Data Tooltips and the Watch Window
2. Displaying Extended Information for LabWindows/CVI-Specific Types
3. Using the Graphical Array View to Analyze Value Trends

Evaluating Compound Expressions Using Data Tooltips and the Watch Window

Hover over variables that are active in the current execution scope of a suspended LabWindows/CVI application to display the value of that symbol in the data tooltip. If the value in the tooltip is bold, you can change it by clicking its value. The data tooltip also evaluates compound expressions containing multiple symbols when you hover over a selected region of text in your source code.

You can also drop compound expressions from your source code in the Watch window to track value changes of variables or custom expressions that you can create yourself while debugging:

Displaying Extended Information for LabWindows/CVI-Specific Types

Sometimes variables of an arbitrary type may hold values representing handles of LabWindows/CVI-specific types:

int panelHandle = LoadPanel (0, “test.uir”, TESTPANEL);

LabWindows/CVI panel handles are usually stored in integer variables, as shown in this example. By default, the Watch window displays the value panelHandle as a number because it is of type int. You can easily change the interpretation of the variable in the Watch window by selecting the Specific Type context menu item. This menu item displays additional information in the Watch window expression, like the number of items for ListType or the current calendar time for time_t variables.

In our example, perform the following steps:

1. Add panelHandle to the Watch window.
2. Right-click the expression in the Watch window to bring up the context menu.
3. Select Specific Type » Panel Handle.

Notice that the expression in the Watch window displays the title of the loaded panel referenced by the panelHandle.

Using the Graphical Array View to Analyze Value Trends

Use the Graphical Array View to visually analyze larger amounts of data in LabWindows/CVI. You can view 1D and 2D arrays in multiple graphs while you are debugging an application. You can open the Graphical Array View from the Variables and Call Stack window, the Watch window or from your source code by right-clicking and select View » Graphical Array View.

One common use case for graphical array displays is identifying uninitialized values. In the following example, the values array is initialized using a trigonometrical parameterized function, but one point is left uninitialized for the purpose of this example:

#define NUM_VALUES 60
#define PI 3.14159

double GenerateValue (int i, int j) {
     return sin (i * (360 / NUM_VALUES) * (PI / 180))
          * cos (j * (360 / NUM_VALUES) * (PI / 180));
}
void main () {
     int i, j;
     double values[NUM_VALUES][NUM_VALUES];
     for (i = 0; i < NUM_VALUES; i++)
          for (j = 0; j < NUM_VALUES; j++)
               if (some_condition (i, j))
                    values = GenerateValue (i, j);
}

The point that is left uninitialized can be seen in the Graphical Array View as a distinct element:

You can also use the Graphical Array View as a tool to visualize mathematical data when debugging an application. Learn about how you can use features like zooming, panning, and changing the style (color, point and line style) to control the way in which the graph is plotted by referring to the View » Graphical Array View help topic in the LabWindows/CVI Help.

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