Basic On Error
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Visual Basic Compiler Error
This documentation is archived and is not being maintained. This documentation is archived and is not being maintained. On Error Statement (Visual Basic) Visual Studio 2015 Other Versions Visual Studio 2013 Visual Studio 2012 Visual Studio 2010 Visual Studio 2008 Visual Studio 2005 Visual Studio .NET 2003 Enables an error-handling routine and specifies the location of the routine within a procedure; can also be used to disable an error-handling routine. Without an On Error statement, any run-time error that occurs is fatal: an error message is displayed, and execution stops.Whenever possible, we suggest you use structured exception handling in your code, rather than using unstructured exception handling and the On Error statement. For more information, see Try...Catch...Finally Statement (Visual Basic).Note The Error keyword is also used in the Error Statement, which is supported for backward compatibility.Syntax Copy On Error { GoTo [ line | 0 | -1 ] | Resume Next } PartsTermDefinitionGoTo lineEnables the error-handling routine that starts at the line specified in the required line argu
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. You can and should do all you can to
Visual Basic On Error Handling
prevent them, but when they happen you have to handle them. Introduction Trapping Errors at Run-Time visual basic on error goto line Building Error Handlers Raising Your Own Errors Summary Introduction The various functions, statements, properties and methods available in Visual Basic and the components visual basic on error resume used in Visual Basic expect to deal with certain types of data and behavior in your applications. For example, the CDate() function can convert a value to a Date variable. The function is remarkably flexible in the type of information https://msdn.microsoft.com/en-us/library/5hsw66as.aspx 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 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 http://www.vb6.us/tutorials/error-handling 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 modules built as components of ActiveX server DLLs or EXEs. It is considered good programming practice to separate the user interface from the program logic as much as possible, so if a server component cannot deal with an error, it should raise the error in its client application rather than simply display an
Database Guide User login Username: * Password: * Request new password Home › Tutorials Error handling in Visual Basic Level: Error handling is essential to http://www.vb6.us/tutorials/error-handling-visual-basic all professional applications. Any number of run-time errors can occur, and http://www.vb-helper.com/tut6.htm if your program does not trap them, the VB default action is to report the error and then terminate the program (often resulting in the end user calling you and complaining, "Your program kicked me out!"). By placing error-handling code in your program, you can trap visual basic a run-time error, report it, and let the user continue. Sometimes the user will be able to correct the error and sometimes not, but simply allowing the program to crash is not acceptable. You should generally place error-handling code in any Sub or Function that accesses files or databases. Your code will typically interrogate the Number and Description basic on error properties of the built-in VB Err object in an error-handling routine set up with the On Error statement. In this section, we will look at the following statements: On Error GoTo label On Error Resume Next Following is a brief tutorial in error-handling. To perform this tutorial, you should have a floppy disk handy. Also, in the VB IDE, make sure that the Break on Unhandled Errors option is set under Tools à Options à General. STEPS: 1. Start a new project. 2. Place four command buttons on the form. Name them and set their Captions as follows: Name Caption cmdCrash Crash cmdGoToLabel GoTo Label cmdGoTo0 GoTo 0 cmdResumeNext Resume Next Your form should look something like this: 3. Code the cmdCrash_Click event as follows: Private Sub cmdCrash_Click() Open "A:\JUNK.TXT" For Input As #1 MsgBox "File was opened successfully" Close #1 End Sub 4. Place your floppy disk in the A: drive. Run the program and click the Crash button. Ass
explains the fundamentals of using error handlers in Visual Basic. There is a lot more to writing bug proof programs than just using error handlers. This book also explains how to reduce the chances of errors occurring in a program, how to detect errors when they do occur, and how to recover from unexpected errors. Visit the book's Web page to learn more. Chapter 12 Error Handling Fundamentals Sections Use On Error Leave Error Handlers Define Error Constants Keep Error Handlers Separate Understand Error Handler Scope Don't Nest Error Handlers Error Handling Slides This chapter explains the family of On Error statements Visual Basic uses to handle errors. It tells how a program installs and removes error handlers, and it explains some of the idiosyncrasies of error handling code. After reading this chapter you will be able to write basic error handlers to protect your programs from the unexpected. Use On Error A Visual Basic program uses the On Error statement to register error handling code. This statement can take one of three forms: On Error GoTo 0 On Error Resume Next On Error GoTo line These forms tell Visual Basic what it should do when the program encounters an error. The three forms are described in the following sections. On Error GoTo 0 On Error GoTo 0 is relatively straightforward. It simply cancels any currently installed error handler assigned by a previous On Error GoTo line or On Error Resume Next. If the program encounters an error after this statement executes, it crashes. On Error Resume Next On Error Resume Next makes the program ignore errors. When it encounters an error, the program continues execution after the statement that caused the error. When a program uses On Error Resume Next, it should check the Err object after every operation that might cause an error. If the value Err.Number is nonzero, the operation caused an error and the program can take special action. The prog