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Subject: FAQ: (6/94) comp.lang.basic.visual.* VB/DOS Frequently Asked Questions

This article was archived around: 5 Jun 1997 14:10:57 -0000

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Last-Modified: June 10, 1994 VISUAL BASIC FOR DOS (VBDOS) Commonly asked Questions & Answers Section IX - B ----------------------------------- PREFACE: This document is a compilation of frequently asked questions and their answers about Visual Basic for DOS which have been gathered from the comp.lang.basic.visual newsgroup. Although some efforts have been made to find obvious errors, there is no guarantee that the information in this document is error-free. The FAQ maintainer, or anyone else associated with this document, assume NO liability for the content or use of this document. If you find any errors, please report them to the address given below. Most FAQs (including this one) are available at the anonymous ftp archive site "rtfm.mit.edu". All four parts of the VB FAQ may be found in the directory "pub/usenet/news.answers/visual-basic-faq". You can also have the VB FAQs e-mailed to you by sending a message to "mail-server@rtfm.mit.edu" with ONLY the text "send usenet/news.answers/visual-basic-faq/*" in the body of the message. As the FAQ maintainer, I don't have time to explore all of the aspects of Visual Basic. I rely on your submissions to improve the quality and inclusiveness of this document. If you have found a VB hint, tip, trick, work-around, etc., please write it up and send it to me! Peter Millardac150@freenet.buffalo.edu - VBDOS FAQ maintainer Table of Contents: 1. How do I use (create) global variables in VBDOS? 2. Does VBDOS make standalone .exe files? 3. What is the current version of the VBDOS compiler? 4. How do I not make a text box beep when I hit the enter key? 5. How does Visual Basic handle shelled tasks? How do I find out when they are finished. 6. How do I break lines of long text into multiple lines of text in the msgbox? 7. What's the difference between MODAL and MODELESS forms? 8. When/Why should I use Option Explicit? 9. Why doesn't PRINT or CLS from a frm module work? 10. How do I invoke FKey traps which won't be triggered by other keys which share the same KeyCode? 11. How do I boost memory available to VBDOS.EXE (the IDE)? 12. My program runs in the IDE, but won't run when compiled?? 13. MISC. Programming TIPS: ----------------------------------------------------------------------------- 1. How do I use (create) global variables in VBDOS? 1.1. VBDOS provides the user with two types of global variables. These are both used in declarations of variables. To share variables between all subs and functions in a specific module, use the SHARED keyword. This makes that specific variable global _in that module_. For example: DIM SHARED CancelFlag AS INTEGER would make the variable CancelFlag a global variable in that module. To share global variables between separate modules, use the COMMON keyword. For example: COMMON SHARED CancelFlag AS INTEGER would make the variable global between all modules that this common statement appears in, and since we are using the SHARED keyword also, this will also be shared in all the subs and functions in the modules which this declare statement appears. All COMMON statements must be matched between modules which the variables should be global in. For example, if you have one set of 10 COMMON statements in one module, and a different set of 10 COMMON statements in another module in the same project, you will get a 'Type Mismatch Error'. Make all COMMON blocks identical in all the modules in a specific project. (See Misc. Programming Tips Below). 2. Does VBDOS make standalone .exe files? 2.1. VBDOS can compile programs in two different ways (user option). It can compile programs to use a RUNTIME file (like a DLL) or can be compiled as a standalone .exe file. 3. What is the current version of the VBDOS compiler? 3.1. VBDOS is currently at version 1.0 4. How do I not make a text box beep when I hit the enter key? 4.1. Put "something else" in your _KeyPress event, depending on what you really want. This code example makes *nothing* happen, for an extended period of time: Sub Text1_KeyPress (KeyAscii As Integer) If KeyAscii = 13 Then '13 is Key_Return KeyAscii = 0 '0 (zero) is nothing End If End Sub This might not be a very nice thing to do, since your users usually have some intention when they press Enter. Usually they will want to jump to the next control, like the Tab key does. You will then change the line KeyAscii=0 to KeyAscii=9 (Key_Tab) in the example above. BTW, you'll also find this in the Microsoft VB KnowledgeBase. They add that you should set the MultiLine property to False. Of course. 5. How does Visual Basic handle shelled tasks? How do I find out when they are finished. 5.1. In VBDOS, all shelled tasks are completed before control returns to the program. No tasks are done while the DOS command is being executed. 6. How do I break lines of long text into multiple lines of text in the msgbox? 6.1. Use the append a chr$(13) to the end of the string to break lines into multiple lines. EG: msg$ = "This is line 1" + chr$(13) msg$ = msg$ + "This is line 2" MSGBOX msg$ 7. What's the difference between MODAL and MODELESS forms? 7.1. Modal forms are forms which require user input before any other actions can be taken place. In other words, a modal form has exclusive focus until it is dismissed. When showing a modal form, the program pauses at the SHOW command until the modal form is either hidden or unloaded. The internal MSGBOX and INPUTBOX$ forms are examples of modal forms. To show a form modally, use the syntax: MyForm.SHOW 1 7.2. Modeless forms are those which are shown but do not require immediate user input. Most child forms (in a MDI application) are typically modeless. To show a form modeless, use the syntax: MyForm.SHOW 8. When/Why should I use Option Explicit? 8.1. Opinions vary greatly on this subject. The main reason to use the OPTION EXPLICIT statement at the top of all modules is to minimize the amount of bugs introduced into your code by misspelling a variable name. Most variants of BASIC (including VB) have the capability to create variables 'on the fly' (without any declarations). This capability can be a double edged sword. At the minimum, it is suggested to use the DEFINT A-Z statement in leu of OPTION EXPLICIT. This statement will cause any variables which are created on the fly to be created as integers as opposed to single precisions. (Integers take up less memory). The OPTION EXPLICIT statement causes VB to 'disable' it's ability to create variables on the fly. Thus, all variables must be declared using a DIM or REDIM statement. All variables not declared will cause an error when the OPTION EXPLICIT statement is used. This will eliminate any bugs when a variable is misspelled. 9. Why doesn't PRINT or CLS from a frm module work? 9.1. To print information to the screen bypassing the desktop, the commands must be issued from a .BAS module. All PRINT/CLS output from a form module is directed to the nul: device. 10. How do I invoke FKey traps which won't be triggered by other keys which share the same KeyCode? 10.1. To trap the only FKeys in events you need to use a combination of the KeyDown, KeyPress, and KeyUp events. The basic concept for this is that _all_ keys trap the UP & DOWN events, while only 'printable' characters trigger the KeyPress event. Thus, when a character key is pressed, it will trigger the KeyDown, the KeyPress, then the KeyUp events (in that order). While a FKey (or arrow, or tab, etc...) will trigger the KeyDown, then the KeyUp events (in that order). The following code uses a textbox tag property to decide whether a printable character is pressed or not. SUB Text1_KeyDown() Text1.tag = "key" END SUB SUB Text1_KeyPress() Text1.tag = "" END SUB SUB Text1_KeyUp() IF Text1.tag = "key" then '--PUT F-KEY HANDLER HERE---- ELSE '--PUT OTHER KEY HANDLERS HERE---- END IF END SUB 11. How do I boost memory available to VBDOS.EXE (the IDE)? 11.1. Try to have as much EMM available as possible. VBDOS.EXE allocates subroutines & functions which are < 16K into EMM. 11.2. To make more conventional mem availble, use the /S:n switch. This will make VBDOS.EXE use a specific amount of conventional memory. A good compromise between speed & memory is /S:340. The lower the n value, the slower the environment runs. 11.3. Running out of DGROUP usually causes most 'out of memory' errors. Possible causes are: 11.3.1.Too many subs & functions exist. Each one takes up 46 bytes of DGROUP. 11.3.2. Large static arrays. All static arrays are stored in DGROUP. If a DIM statement is for a COMMON SHARED statement, the array becomes static. Make the COMMON SHARED statement appear before the DIM statement to make the array Dynamic & therefore will not be stored in DGROUP. 11.3.3. Variable Overhead. Each var has a 4 byte overhead for _each_ module. For multiple modules projects which use lots of Global (COMMON) statements, this overhead is repeated for _each_ module. 11.4. Possible causes for running out conventional memory: 11.4.1. Not enough EMM. 11.4.2. Subs or functions which exceed 16K. 11.4.3. Large arrays. Non-variable length string arrays can be stored in EMM using the /ea switch. 12. My program runs in the IDE, but won't run when compiled?? 12.1. Arrays are dynamic by default in the IDE, but when they are compiled, they are static by default. Therefore, they are stored in DGROUP instead of the far heap. Use '$DYNAMIC to make all arrays dynamic or use REDIM instead of DIM. 12.2. Program generates a "program memory overflow" during compile. You need to break a single module into multiple ones. 13. MISC. Programming TIPS: 13.1. When useing the form designed, to continuously draw controls of a specific type, hold down the control key when clicking on the appropriate control from the tool- box. 13.2. Use the INCLUDE statement to manage large numbers of COMMON SHARED statements, user defined data types, or external function DECLARES. To use an include file, simply put all the VBDOS statements that will be shared into a single file. Save the file as something appropriate. (Typical naming convention is to use an extension of .BI for basic include files). Then simply insert the line: 'INCLUDE: 'foobar.bi' into either your .BAS module, or the module level code in a form. -- Kris Nosack knosack@park.uvsc.edu >>>---> Be strange, but not a stranger! <---<<<