Chapter 6
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Running and Debugging VIs
You upgraded the operating system software, which changed the path to a file or the functionality of a VI or library. You might notice a problem in a VI or a system program.
Error Handling By default, LabVIEW automatically handles errors by suspending execution. You can choose other error handling methods. For example, if an I/O VI on the block diagram times out, you might not want the entire application to stop. You also might want the VI to retry for a certain period of time. In LabVIEW, you can make these error handling decisions on the block diagram of the VI. VIs and functions return errors in one of two ways—with numeric error codes or with an error cluster. Typically, functions use numeric error codes, and VIs use an error cluster, usually with error inputs and outputs. Refer to the Error Clusters section of this chapter for more information about error clusters. Error handling in LabVIEW follows the dataflow model. Just as data flow through a VI, so can error information. Wire the error information from the beginning of the VI to the end. Include an error handler VI at the end of the VI to determine if the VI ran without errors. Use the error in and error out clusters in each VI you use or build to pass the error information through the VI. As the VI runs, LabVIEW tests for errors at each execution node. If LabVIEW does not find any errors, the node executes normally. If LabVIEW detects an error, the node passes the error to the next node without executing that part of the code. The next node does the same thing, and so on. At the end of the execution flow, LabVIEW reports the error.
Error Clusters The error in and error out clusters include the following components of information: •
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status is a Boolean value that reports TRUE if an error occurred. Most VIs, functions, and structures that accept Boolean data also recognize this parameter. For example, you can wire an error cluster to the Boolean inputs of the Stop, Quit LabVIEW, or Select functions. If an error occurs, the error cluster passes a TRUE value to the function.
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LabVIEW User Manual