Error Handling Techniques Visual Basic
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Database Guide User login Username: * Password: * Request new password Home › Tutorials Error Handling In Visual Basic Level: Despite your best efforts to cover all possible contingencies, run-time errors will occur in your applications. error handling in vb You can and should do all you can to prevent them, but when they
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happen you have to handle them. Introduction Trapping Errors at Run-Time Building Error Handlers Raising Your Own Errors Summary Introduction The error handling sql various functions, statements, properties and methods available in Visual Basic and the components used in Visual Basic expect to deal with certain types of data and behavior in your applications. For example, the CDate() function https://msdn.microsoft.com/en-us/library/ms973849.aspx can convert a value to a Date variable. The function is remarkably flexible in the type of information it can accept, but it expects to receive data that it can use to derive a date. If you provide input that it can't convert, it raises error number 13 - "Type mismatch" - essentially saying "I can't handle this input data." In an application, this type of error may be a http://www.vb6.us/tutorials/error-handling program logic error (you simply passed the wrong data) or it may be a data entry error on the part of the user (you asked for a date and the user typed a name). In the first case, you need to debug the program to fix the mistake. However, there is no way for you to anticipate the behavior of the end users of the application. If the user enters data you can't handle, you need to deal with the situation. Dealing with errors at run-time is a two step process: Trap the Error Before you can deal with an error, you need to know about it. You use VB's On Error statement to setup an error trap. Handle the Error Code in your error handler may correct an error, ignore it, inform the user of the problem, or deal with it in some other way. You can examine the properties of the Err object to determine the nature of the error. Once the error has been dealt with, you use the Resume statement to return control to the regular flow of the code in the application. In addition to dealing with run-time errors, you may at times want to generate them. This is often done in class
at the time the application is being used. Some other problems could be caused by the computer on which the application is being used. While developing your application, you should anticipate as many problems as possible as take appropriate actions. Error Categories There are http://www.functionx.com/visualbasic/exceptions/errorhandling.htm three main types of errors that could occur while your application is being used: Syntax Errors: A syntax error comes from your mistyping a word or forming a bad expression in your code. It could be that you misspelled a keyword such as ByVel instead of ByVal. It could also be a bad expression. Examples are: 524+ + 62.55 if Number == 2 Number = 6 If you use the Microsoft Visual Basic IDE to write your code, it would point out the errors while you error handling are writing your code, giving up time to fix them. There are other syntax errors that the IDE may not detect. This could come from using a data type or class that doesn't exist. When you compile your application, the compiler can let you know about other syntax errors. Those types of errors are those the compiler cannot execute. It this case, the compiler intercepts, stops, and lets you know. For this reason, syntax errors are almost the easiest to fix. Most of the time, error handling techniques the compiler would point out where the problem is so you can fix it. Run-Time Errors: After all syntax errors have been fixed, the program may be ready for the user. The time period a person is using an application is called run-time. There are different types of problems that a user may face when interacting with your program. For example, imagine that, in your code, you indicate that a picture would be loaded and displayed to the user but you forget to ship the picture or the directory of the picture indicated in your code becomes different when a user opens your application. In this case, when you compiled and executed the application in your machine, everything was fine. This is a type of run-time error. Run-time errors are mostly easy to fix because you will know what the problem is occurring and why. Logic Errors: These are errors that don't fit in any of the above categories. They could be caused by the user misusing your application, a problem with the computer on which the application is running while the same application is working fine in another computer. Because logic errors can be vague, they can also be difficult to fix. One of the best qualities of an effective programmer is to anticipate as many problems as possible and to deal with them in the early stages. Some problems can be easy to fix. With some others, you will simply need more experience to know how to fix them. Unfortunately, it will n
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