On Error On Vb6
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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. You can and should do all you can on error vba to prevent them, but when they happen you have to handle them. Introduction Trapping Errors at
On Error Goto Line
Run-Time Building Error Handlers Raising Your Own Errors Summary Introduction The various functions, statements, properties and methods available in Visual Basic and the components on error exit sub 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 on error goto 0 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 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
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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 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 simp
Database Guide User login Username: * Password: * Request new password Home › Tutorials Error handling in Visual Basic Level: Error handling is essential to all professional applications. Any number of run-time errors can occur, and if your program vba on error goto 0 does not trap them, the VB default action is to report the error and then vb6 on error resume next terminate the program (often resulting in the end user calling you and complaining, "Your program kicked me out!"). By placing error-handling
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code in your program, you can trap 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 http://www.vb6.us/tutorials/error-handling 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 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 http://www.vb6.us/tutorials/error-handling-visual-basic 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. Assuming that you do not have a file called "JUNK.TXT" on your A: disk, the program will "bomb" with the code/message "53 – File Not Found". If you don't have a disk in drive A:, the code/message will be "71 – Disk Not Ready". 5. Code the cmdGoToLabel_Click event: Copy and paste the code from the Crash sub, and add statements so that the cmdGoToLabel_Click Sub looks like the following (the new statements are shown in bold): Private Sub cmdGoToLabel_Click() On Error GoTo OpenFileError Open "A:\JUNK.TXT"
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