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README.TXT Release Notes for Microsoft (R) Visual Basic (TM) for MS-DOS (R) Professional Edition Version 1.00 (C) Copyright Microsoft Corporation, 1982-1992 This document contains release notes for version 1.00 of Microsoft Visual Basic for MS-DOS. Information in this document is more current than that in the manuals. Information in online Help may also be more current than that in the manuals. Microsoft revises its printed documentation at the time of reprinting, so manuals with document numbers ending in numbers higher than "0992" may include the corrections listed in parts 2-4. Document numbers are found on the copyright page of each manual. =========================================================================== Contents =========================================================================== Part Description ---- ----------- 1 Notes on Using Microsoft Visual Basic 2 Corrections to "Microsoft Visual Basic Programmer's Guide" 3 Corrections to "Microsoft Visual Basic Reference" 4 Corrections to Online Help 5 Corrections to "Microsoft Visual Basic Professional Edition" =========================================================================== Part 1: Notes on Using Microsoft Visual Basic =========================================================================== This part contains the following sections: 1.1 Tips and Tricks 1.2 Forms 1.3 Language 1.4 LINK 1.5 Hardware Considerations 1.6 TRNSLATE.EXE 1.7 Custom Controls 1.8 CodeView 1.9 Overlays 1.10 ISAM 1.11 BUILDRTM 1.12 PROFILE ------------------- 1.1 Tips and Tricks ------------------- Programming Environment Speed vs. Capacity ------------------------------------------ The programming environment (VBDOS.EXE) has been overlayed to increase capacity. The default in-memory size of VBDOS.EXE is tuned to provide a good speed/capacity tradeoff. If the environment seems slow to you, you can increase speed by using the /S:n command-line switch. This switch specifies the in-memory size of VBDOS.EXE. The default is approximately 350K. To increase performance, specify a value greater than the default. To increase capacity, specify a value less than the default. For more information, refer to Appendix B, "Memory Management" in the "Programmer's Guide." Memory Configuration Suggestions -------------------------------- For systems running MS-DOS 5.00 and later, load MS-DOS and TSRs high to free as much conventional memory as possible. Optimal configurations for conventional, Extended memory (XMS), and Expanded memory (EMS) vary depending on the type and amount of memory available on your system. The following recommendations cover 1 MB, 2 MB, and =>3 MB configurations. 1 MB memory: If you have no XMS or EMS, the programming environment swaps to disk and all code is stored in conventional memory. To increase performance, set the /S:n command-line option to a value greater than 350 (default). This will reduce overlay swapping. To increase capacity, set the /S:n command-line option to a value less than 350. This reduces the in-memory size of the programming environment, providing more far memory for your program; overlay swapping increases however. 2 MB memory: If you have XMS, use a memory manager such as EMM386 to configure all available memory above 1 MB as EMS. EMS can be used by the programming environment for overlay swapping as well as for program code and data storage. If you do not have a memory manager that can configure XMS memory as EMS memory, or if you do not need EMS for code and data storage, use HIMEM.SYS to allow access to XMS memory for overlay swapping. HIMEM.SYS uses less conventional and XMS memory for itself than memory managers, such as EMM386. 3 MB or more memory: Configure 1.5 MB as XMS for programming environment overlay swapping and divide the remaining memory between EMS and disk caching (such as SMARTDRV.SYS). EMS provides more memory for program code and data and disk caching provides faster file access. Debugging Compiled .EXEs ------------------------ You must use the /D compiler switch to enable Out of Stack space, array bounds, and overflow checking in the compiled code. In addition, /D enables CTRL+BREAK at run-time in compiled .EXEs. This error checking is provided automatically in the programming environment. Using VBDOS.EXE and Windows --------------------------- Since VBDOS.EXE is opened for reading while it is being run (due to overlay support), you cannot automatically run VBDOS.EXE in two MS-DOS sessions with SHARE.EXE loaded. To allow running VBDOS in multiple sessions, make VBDOS.EXE read-only on your hard disk. Ending Execution While Debugging -------------------------------- Pressing CTRL+BREAK while executing an application in the programming environment returns you to the currently executing code -- if a form is waiting for an event, you are returned to the code that invoked the form: either the module level of the start-up form or a SHOW method. Terminating the application normally (by closing the last form, for example) returns you to your former location in code. Inserting Special Characters ---------------------------- To insert a special character in the Code window or in the Settings box in the Properties bar: 1. Set NUMLOCK on. 2. Press CTRL+P. 3. Hold down the ALT key and type the ASCII code of the character using the numeric keypad. 4. Release the ALT key. Note that this process may not work for some characters below ASCII 28. In those cases, use the CHR$ statement to insert special characters in code. For example: x$ = CHR$(21) ' Section symbol. To insert a special character in a form application at runtime (for example, when typing in a text box): 1. Set NUMLOCK on. 2. Hold down the ALT key and type the ASCII code of the character using the numeric keypad. 3. Release the ALT key. Printing -------- PRINT method output (PRINT from a form module) always goes to the active form whether or not that form is visible. PRINT statement output (PRINT from a code module) always goes to the screen unless qualified by a form reference (FORM1.PRINT. The PRINT statement cannot be used when forms are showing. To send output to the screen from a form-based application, you must first hide all visible forms (SCREEN.HIDE) and then use the PRINT statement from a code module. PRINT from the Immediate window applies to the currently active module if in a CTRL+BREAK state or to the Startup module if not in an edit-and-continue state. Therefore, if a code module is active, PRINT from the Immediate window is treated like the PRINT statement and the rules outlined above apply (PRINT statement not allowed when forms are showing). If the active module is a form module, PRINT from the Immediate window is treated like the PRINT method and applies to that form, whether or not it is visible. Code Cleanup ------------- If you save your files in binary format, variable name table entries are preserved even after you have deleted all instances of a variable name. To eliminate these entries, save your files as text (ASCII) and then resave as binary. This increases capacity within the programming environment and reduces the size of your source files. Visual Basic does not automatically remove unused event procedure templates that you create with the Edit Event Procedures dialog box. Make sure you delete all unused procedure templates before completing your project. Form Redraw ----------- The form painting and redraw algorithms in Visual Basic may not always refresh the screen at the time you expect. This is because they have been optimized to provide the best speed/redraw compromise. To repaint a form or control at any time, use the object's REFRESH method. For instance, PRINT output on a nonactive form may overwrite the shadow of the active form, since PRINT does not cause a form refresh. Use the REFRESH method on the active form after the PRINT method to redraw the shadow. Accessing Network Drives ------------------------ Setting the Drive or Path properties to a network drive may hang your application if the drive has disconnected. Variable Names -------------- Avoid using scalar variable names of the form "A.B". This type of variable naming is not supported Visual Basic for Windows and increases load time due to the special parsing that is required. Use the "." notation only when referencing properties, methods, or elements of a record variable. Replace variables of the form "A.B" with variables of the form "A_B". Avoid using variable names that are also the names of properties or ControlPanel constants. Doing so can make it difficult to debug an application. Because the Help system recognizes these names, symbol Help for these variables is inhibited. To work around this problem, rename VBDOS.HLP then request help on the variable. The programming environment displays an error dialog box. When you choose Cancel, the programming environment displays symbol Help for the variable. Exiting When Out of Memory During Binding ----------------------------------------- If you run out of memory while binding in the programming environment, Visual Basic displays a dialog box with the "Out of Memory" error message. In some cases, choosing OK only redisplays the dialog box. If this occurs, pressing the SPACEBAR instead of ENTER may break the loop. Math Coprocessor Performance ---------------------------- Memory managers such as EMM386 and 386MAX will slow performance of math operations using a coprocessor. For best results, do not have a memory manager resident when performing intensive math calculations using a coprocessor. Distinguishing Between Apostrophe and Right Arrow Keys ------------------------------------------------------ The apostrophe (') and right arrow keys both return key codes of 39 in key event procedures. To distinguish between these keys in code, use a combination of the KeyDown, KeyUp, and KeyPress events as shown below: SUB Form_KeyDown (KeyCode AS INTEGER, Shift AS INTEGER) SELECT CASE KeyCode CASE 39 IF Shift = 0 THEN Tag = "arrow" ELSE Tag = "" CASE ELSE END SELECT END SUB SUB Form_KeyPress (KeyAscii AS INTEGER) IF KeyAscii = 39 THEN Tag = "" PRINT CHR$(KeyAscii); END SUB SUB Form_KeyUp (KeyCode AS INTEGER, Shift AS INTEGER) IF KeyCode = 39 AND Tag = "arrow" THEN PRINT CHR$(16); END SUB The preceding code takes advantage of the fact that KeyPress does not detect arrow keys -- if the key is detected in that event procedure, the code sets the form's Tag property to "" and prints the character. The Tag property is then used in the KeyUp event procedure to print a "" character if KeyCode 39 is detected. --------- 1.2 Forms --------- Ending Form Applications ------------------------ If your compiled application has a hidden form and then unloads the last visible form, the system appears to stop. This occurs because there is still a loaded form, but no way to access it. To avoid this, end your applications explicitly using an END statement or its equivalent, rather than relying on UNLOAD. Note that reading or setting an unloaded form's properties or controls implicitly loads that form without displaying it. This is the most common way to get into the situation described above. Visibility ---------- Hiding a modal form makes that form nonmodal. Hiding an MDI form hides all of its children: Thus, any modal children will no longer be modal when they are shown again (unless explicitly shown again as modal). SCREEN.HIDE hides all visible forms: Thus, modal forms will be hidden and will no longer be modal when they are shown again (unless explicitly shown as modal). You can change the Visible property of child controls while their parent is hidden, but the Visible property of child controls will return False (0) as long as the parent is hidden. For example: frmOpen.Visible = 0 ' Hide parent form. cmdState% = frmOpen.cmdExit.Visible ' cmdState% will be 0 (False) frmOpen.cmdExit.Visible = NOT cmdState% ' Change Visible property. frmOpen.Visible = -1 ' Show form again. In the preceding code, you might expect the third line to toggle the visibility of the command button. Instead, it sets Visible to True (NOT 0 = -1), regardless of the initial setting of cmdExit.Visible. Menus and Timer Events ---------------------- While a menu control has focus, timer events and ON <event> trapping are suspended. When the menu control loses focus, timer events and ON <event> trapping resume. Insert State ------------ Forms programs maintain the insert state internally. There is no way to programmatically switch between insert and overstrike in a text box. Monochrome Displays ------------------- For best appearance on monochrome displays, you should avoid 3-D. For example, the following turns off 3-D if a system does not have color or grey scale capability: SUB CheckMono ( ) ON LOCAL ERROR GOTO SetNo3D SCREEN.HIDE SCREEN 1 ' SCREEN 1 requires minimal graphics. ON LOCAL ERROR GOTO 0 SCREEN 0 SCREEN.SHOW EXIT SUB SetNo3D: SCREEN.ControlPanel(THREE_D) = 0 RESUME NEXT END SUB When creating form applications for users with monochrome monitors, be aware that the default color setting for access keys may display as bright white on bright white on some monitors. For applications that target this hardware, you may want to rely on tab order rather than access keys to provide a keyboard interface. The sample applications included with Visual Basic are written for color monitors and monitors that support grey scale. If they do not display properly on your system, turn off 3-D in their form load event procedures. Setting ForeColor Property -------------------------- SCREEN.ControlPanel(THREE_D) must be set to FALSE (0) for changes to the ForeColor property to affect the border of a control. While THREE_D is TRUE (-1), Visual Basic supplies the border color. Symbol Help on Controls ----------------------- You cannot get Help on a control if it is not referenced in code from its parent form. For example, in module ONE.FRM: SUB frmONE_Click() cmdOK.Visible = FALSE END SUB In module TWO.FRM: X$ = frmONE.cmdOK.Tag Y$ = frmONE.fraHelp.Tag In the preceding example, pressing F1 on cmdOK displays symbol Help on the control, but pressing F1 on fraHelp only beeps. Maximum Number of Controls -------------------------- The maximum number of controls on a form is 254. Maximum Number of Timers ------------------------ You cannot have more than 16 active timers at any one time. A timer is active if its Enabled property is True and its Interval property is nonzero. Custom controls that function as timers also apply to this limit. This limit does not apply to inactive timers. Forms in Quick Libraries ------------------------ You can create Quick libraries out of form modules by following the same procedures for Basic code modules. To access the properties of a Quick library form or control in your application, you must declare the Quick library form by manually inserting a $FORM metacommand at the module level of the calling code. With project files, the programming environment automatically inserts '$FORM metacommands as needed. However, the programming enviroment cannot do this for forms in Quick libraries, since they are already compiled. Accessing Width and Height Properties Before Forms are Visible -------------------------------------------------------------- To ensure correct values for a form's Width and Height properties and SCREEN.Width and SCREEN.Height, execute a SHOW method before using them. "Overflow" with ASCII Forms --------------------------- The Form Designer generates an "Overflow" error message if the absolute coordinates of an object exceed 255. This can occur only with ASCII form descriptions created outside of the Form Designer. "Absolute coordinates" are the values that result from combining the Top + Height or Left + Width property values of a control and its parents. When these combine in a way that the right edge or bottom edge of a control exceeds 255, the "Overflow" error results. To fix this, you must reduce the Top, Height, Left, or Width property values of the object or its parents in the ASCII form using an ordinary text editor. Child Form Placement in MDI Form_Load Event ------------------------------------------- To ensure the correct display of child forms and print output, add a SHOW statement as the first line of the Form_Load event procedure of any form that is an MDI container. For example: ' Event procedure in frmMDI.FRM. SUB Form_Load ( ) frmMDI.SHOW END SUB This forces a redraw event which sets the MDI container's ScaleHeight and ScaleWidth properties to their maximized settings, rather than the design-time settings. Option Buttons and Modal Operations ----------------------------------- Option buttons sometimes require multiple clicks to become selected if the code in their click events include modal operations such as displaying a MSGBOX or hiding forms. For example, the following code requires multiple clicks to select option buttons Option1 or Option2: SUB Option1_Click () SCREEN.HIDE WIDTH , 43 SCREEN.SHOW END SUB SUB Option2_Click () SCREEN.HIDE WIDTH , 25 SCREEN.SHOW END SUB Separator Bar as First Menu Item -------------------------------- If you specify a separator bar as the first menu control below a top-level menu item, you won't be able to select menu items in that list using the keyboard. KeyUp Events and Menus ---------------------- KeyUp events for the active control will be generated when using access or shortcut keys for menus. To differentiate between menu generated KeyUp events and user generated KeyUp events for the active control, set a flag in the control's KeyDown event procedure that can be tested before processing keys in the KeyUp event procedure. Child Form Width and Resize Events ---------------------------------- If a child form has the same width as its MDI container, it will not generate a resize event when maximized. Height and Width of Attached Scroll Bars ---------------------------------------- The Height and Width properties of scroll bars that are attached to a form do not return accurate values when the form is first displayed. Height and Width return accurate values after a resize event occurs. Printing Attached Scroll Bars ----------------------------- Scroll bars that are attached to a form do not print if the the form is not active when the PRINTFORM method is invoked. Forms Disable Blinking ---------------------- Using MSGBOX, INPUTBOX$, or forms disables the blinking bit in MS-DOS. To re-enable blinking and restore correct COLOR statement settings when forms are not showing, call the MS-DOS interrupt 10H. For example: ' Requires VBDOS.QLB for CALL Interrupt. REM $INCLUDE: 'vbdos.bi' DIM inregs AS regtype, outregs AS regtype CLS COLOR 26, 6 ' Blinking green on red. PRINT "Blinking text" SLEEP 1 ' Pause screen.controlpanel(7) = 0 ' Preserve background. MSGBOX "Click OK." ' MSGBOX turns off blinking ' and changes colors. ' These statements restore colors and blinking. inregs.ax = &H1003 inregs.bx = 1 CALL interrupt(&H10, inregs, outregs) Passing Control Array Elements ------------------------------ You cannot pass an entire control array to a procedure as an argument. When you pass a control array element to a procedure, you pass only that instance of the control, as in the following example: type% = IsCmdBtn%(RandomControl(1)) ' Pass control array element to procedure FUNCTION IsCmdBtn%(X AS CONTROL) IF TYPEOF X IS CommandButton THEN FindType% = TRUE ELSE FindType% = FALSE END IF END FUNCTION Note that you can't discern that X refers to a control array element once the control is passed to the procedure. In compiled programs, you cannot pass a control array element into a procedure, then load it from that procedure. For example, the following code generates the error "Control array element does not exist" if executed in a compiled program: LoadIt cmdButton(1) SUB LoadIt (X as CONTROL) LOAD X END SUB Note that the preceding code will run in the programming environment without an error. This difference occurs because compiled applications are "early bound." TabStop Property ---------------- Using access keys on a form where all controls have TabStop = FALSE will cause unpredictable results. ------------ 1.3 Language ------------ String Literals in Memory ------------------------- String literals (i.e. quoted strings "This is a string") are stored in far memory. All string literals in a form or code module are stored in their own 64K segment. Thus, storage for string literals no longer comes out of DGROUP. Line Continuation ----------------- When loading or compiling Basic code created outside of the programming environment, the underscore character (_) may be used to continue a line if it is preceded by a tab or space. Terminating a line with the underscore alone causes an error. The programming environment automatically joins continued lines and removes line-continuation characters when you load code. Note that the underscore without a preceding space can now be used in symbol names. Keyword Conflicts ----------------- When loading a SUB or FUNCTION with an invalid definition -- a parameter list contains a variable with the same name as a reserved word -- that SUB or FUNCTION definition will not be recognized; instead it will be placed at the module level and flagged as an error. The code contained in the procedure will also be placed at module level. If this occurs, orrect the invalid definition and reload the file. Calling C Routines From Basic ----------------------------- If you are writing C routines to use with Basic, you should be aware that all routines that Basic calls that can cause an error (either directly or indirectly, including math errors and divide-by-zero) must set up a BP frame. However, the Microsoft C Compiler optimizes away the BP frame if the routine has no parameters or local variables. If this occurs, you can rectify the problem by turning off optimizations when compiling your C routine or by adding a local variable to the routine. RMDIR "." --------- Using RMDIR with "." generates the error "Path not found." You cannot remove the current directory. User-Defined Error Numbers -------------------------- Error number 105 is used by the system as a temporary error number and should not be used as a user-defined error number in your programs. If used, it halts execution of your application but does not generate the error message, "Unprintable Error," as other unassigned error numbers do. Setting ERR ----------- You cannot use the ERR statement with arguments greater than 255. To work around this, use ERROR to generate the error. For example: ON ERROR RESUME NEXT ERROR 431 PRINT ERR FRE(-3) and Overlays -------------------- Using FRE(-3) in a compiled program is no longer supported and will return the error message "Feature Unavailable." GET, PUT, SADD, SWAP, VARSEG, VARPTR$ ------------------------------------- Visual Basic permits you to use form variables with these statements and functions, but such use is not meaningful and will cause unpredictable results. For example: SUB ChangeCaption (X AS FORM) DEF SEG = VARSEG (X) ' May cause system to stop. ' Other code ommitted. END SUB Using MSGBOX, INPUTBOX$ with Existing Code ------------------------------------------ By default, these statements display the default form background pattern. To preserve your screen, set the ControlPanel(DESKTOP_PATTERN) property. For example: LOCATE 10, 10 : PRINT "Preserve this text" SCREEN.ControlPanel(7) = 0 ' 7 = DESKTOP_PATTERN MSGBOX "This is displayed without blanking screen." OPTION EXPLICIT and Immediate Window ------------------------------------ If your program uses OPTION EXPLICIT, you must declare any variables used in the Immediate window. For example: DIM i%: FOR i% = 1 to 10: PRINT i%: NEXT -------- 1.4 LINK -------- The Microsoft Segment-Executable Linker (LINK) can make use of a DPMI server such as 386MAX or Windows enhanced mode. LINK runs fine without a DPMI server, however. If it cannot locate a DPMI server, LINK displays a warning message and then executes in real mode. --------------------------- 1.5 Hardware Considerations --------------------------- Phantom Drive Support --------------------- Accessing the phantom drive (drive B on a single-floppy system) when forms are showing on the screen causes the operating system to print the message "Insert diskette for drive B: and press any key when ready" if the B drive is not considered active. This message is printed on top of any visible forms at the current cursor location. To respond to this message and allow the operating system to continue, the user must ensure the drive door is closed and then press any key. Your program cannot trap this message using error handling, but you can intercept problems before they occur by searching a drive list box for the "B:" specification and then prohibiting your program from switching to the B: drive if it is not present. For example, the following code uses a drive list box (Drive1) to check if a B: drive exists and sets a flag to TRUE if it does: ' Module level DIM SHARED BFlag AS INTEGER SUB Form_Load ( ) FOR i% = 0 to Drive1.ListCount IF INSTR(Drive1.List(i%), "B:") THEN BFlag = TRUE NEXT END SUB Invalid Drive on Start-Up ------------------------- Make sure the current drive is valid (the drive exists and contains a disk) before starting VBDOS, FD, or running an application with a directory list in the programming environment. If the drive is not valid, you may receive an "Out of memory" error message. French Keyboards ---------------- In the Form Designer, the M accelerator key does not work if your cursor is in an edit field. In the programming environment, bookmarks do not work correctly with this keyboard driver. Monochrome Monitors ------------------- Some systems with monochrome monitors may not display the programming environment and Form Designer correctly. Applications created with Visual Basic will display correctly on these systems, however. ATI Ultra VGA Video Cards ------------------------- Systems with this card may wrap the first character of print output to the end of the preceding line in screen mode 10. InColor Hercules Video Cards ---------------------------- The programming environment and the Form Designer display in black and white on systems with this card. In addition, text box controls do not display a cursor on these systems. SCREEN 13 with SpeedStar VGA Video Cards ---------------------------------------- Screen mode 13 causes display anomalies on the output screen with SpeedStar VGA video cards. This occurs when displaying the output screen with F4 and when stepping through an application in the programming environment. Aspect Ratio with Wyse EGA and CGA Video Cards ---------------------------------------------- Use an aspect ratio of 1.2 when drawing circles on Wyse EGA and CGA video cards to make circles appear round. ---------------- 1.6 TRNSLATE.EXE ---------------- For specific information on language differences between Visual Basic for Windows and Visual Basic for MS-DOS, see the "Programmer's Guide" appendixes E, G, H, and I and the file COMPAT.TXT. VBDOS.EXE, VB.EXE, and FT.EXE ----------------------------- All of these executables must be in directories in your PATH environment variable when you run TRNSLATE.EXE. Character Mappings ------------------ TRNSLATE.EXE and FT.EXE do not map extended ASCII characters (>128) to their ANSI equivalents and vice versa. For this reason, it is a good idea to replace extended characters, such as umlauts, with non-extended characters before converting your application. Note that using extended ANSI characters in a form or control name in Visual Basic for Windows results in an invalid form or control name in Visual Basic for MS-DOS. ------------------- 1.7 Custom Controls ------------------- Cannot Cancel Load or Unloads ----------------------------- You cannot return a error from the custom control load or unload event -- Custom1_CustomUnload -- to prevent your custom control from being loaded or unloaded. Load or unload prevention is not possible, and returning an error from these functions can de-stabilize the system and cause it to stop. Thus, if you use the InvokeEvent callback to provide an Unload event procedure for your custom control to your users, you must ignore the Cancel parameter or map its meaning to something else, since you cannot cancel the unload process. This applies to control array elements as well as to controls being unloaded due to form unload. SetAttribute Routine -------------------- Use the SetAttribute callback routine to specify an access key for a custom control, allow the control to reject focus, reject arrow-key trapping, or control the display of a text cursor on the control. In Basic, declare SetAttribute as follows: DECLARE SUB SetAttribute (BYVAL ControlID AS INTEGER, _ BYVAL AttributeID AS INTEGER, BYVAL Value AS INTEGER) Parameter Description ----------- ------------------------------------------------------------- ControlID ControlID property of the custom control. AttributeID Attribute to set. Value Setting of the attribute. Constant values for AttributeID are contained in the CUSTINCL Include files and have these values: Settings for AttributeID Settings for constant (literal) Description Value parameter ------------------------ ------------------------- -------------------- ATTR_AccessKey (0) Specifies ASCII ASCII code of key code of access key. (not case-sensitive) ATTR_AcceptFocus (1) Specifies whether control TRUE (-1) can receive focus. FALSE (0) ATTR_TrapArrowKeys (2) Specifies whether control TRUE (-1) can detect arrow FALSE (0) keys in Key events. ATTR_TextCursor (3) Determines the style of 0 - 2 cursor on the control. ATTR_AccessKey - Value is the ASCII code for the access key. The key is not case-sensitive (A = a). You can have only one access key per control. You must display the string containing the access key on your control, parse the &, and highlight the access-key character (as is done for standard controls such as command buttons). A Value of 0 (default) specifies no access key. ATTR_AcceptFocus - TRUE (default) allows the control to have focus. FALSE makes the control act like a label and reject the focus (focus passes to the next control in TabIndex). ATTR_TrapArrowKeys - TRUE (default) enables arrow key (up, down, left, right) trapping in the key-handling event procedures. FALSE does not trap these keys and allows arrow keys to act like TAB (as with command buttons). ATTR_TextCursor - Displays a text cursor at CurrentX, CurrentY on your custom control. This text cursor follows CurrentX and CurrentY until turned off. This is useful for creating custom textboxes or for showing focus. Value is enumerated as follows (constants are defined in CUSTINCL include files): Settings for Value Constant (Literal) Description ------------------ ----------------------------- TC_NoCursor (0) No text cursor (default). TC_Underscore (1) Blinking underscore cursor. TC_Block (2) Blinking block cursor. Note that changing the text cursor for a custom control also changes the cursor on the active control if that control displays a cursor. (If this happens, the original cursor for the active control is restored when the control loses, then regains focus.) Using SetAttribute on a standard control may produce unpredictable results. Passing an invalid AttributeID does the same, as does passing an invalid Value for the given AttributeID. Cursor Coordinates ------------------ CurrentX and CurrentY are relative to the current control. When there are multiple containers for a control, the absolute coordinates of CurrentX and CurrentY may exceed 255. In this situation, there is a remote chance that the cursor may reappear on the screen at a seemingly random location. When writing a custom control that displays a cursor, you should test the behavior of your control when absolute CurrentX and CurrentY coordinates exceed 255. "String formula too complex" Error ---------------------------------- Custom controls may cause this error if you have not defined a handler for the ADDITEM method. The CUSTGEN utility generates a handler for this method if you include MthAddItem in the Template Events list box. Restoring TabIndex ------------------ Setting CurrentX, CurrentY, or Interval within custom control code may reset TabIndex, accidentally. To avoid this, store the TabIndex property before setting CurrentX, CurrentY, or Interval, then restore TabIndex. ReadOnly and Enabled Properties ------------------------------- Setting one of these properties for a custom control inadvertantly sets the other to the same value. If you use the ReadOnly property in your custom control, trap the value when set and store it internally in your custom control code. Use this internal value to control ReadOnly behavior to and return the correct value to the user whenever the property is read. Run-time Only Properties ------------------------ The values of the following properties will not be saved at design-time: Drive, FileName, Path, SelText, Text These properties should be used as run-time only properties and masked out at design-time. ------------ 1.8 CodeView ------------ The version of CodeView supplied with Visual Basic for MS-DOS (4.02) is newer than that supplied with Microsoft C/C++ 7.0. This newer version can be used with C7. The same is true for CVPACK.EXE and LINK.EXE. CodeView requires a memory manager such as HIMEM.SYS, Microsoft Windows, or 386MAX. CodeView also requires a 80286/386/486 processor. Variables are Case-Sensitive ---------------------------- Use of variable names within CodeView is case-sensitive. Any reference to a variable from the Command window or within a watch expression must match the case used when the variable was first declared. In addition, if you have variable of the same name but different case within scope, CodeView will only look for the variable that matches the case of the first instance. Viewing Basic String Variables in CodeView ------------------------------------------ You cannot directly watch the value of a Basic string in CodeView. To view the value of a string variable, use the b$sd routine from the Command window. Syntax for b$sd is as follows: b$sd(&stringvar),S The argument stringvar is the name of a string variable minus the type-declaration character (if used). If the variable is a formal parameter within a procedure, omit the &. For example: In code In CodeView Command window Type of string -------------------- ---------------------------- ---------------------- DIM X$ >?b$sd(&X),S With type character DIM Y AS STRING >?b$sd(&Y),S Without type character Z$ = X$ + " " >?b$sd(&Z),S Automatic variable SUB Foo(ABC as STRING) >?b$sd(ABC),S Formal parameter If you omit the ,S option, CodeView returns a pointer to the string address rather than the value of the string. Viewing Numeric Arrays and Fixed-Length String Variables -------------------------------------------------------- Since you can view the data at specific memory locations in CodeView, you can see the values of numeric arrays and fixed-length string variables in hexadecimal with a little ingenuity. Things to Avoid --------------- Do not set breakpoints on form objects using the BP command in the Command window (for example, >BP Form1). Doing so can cause unpredictable results during subsequent execution. Be sure to terminate your Basic application before exiting CodeView. Exiting while execution is suspended may cause problems in restoring the MS-DOS cursor and may cause errors the next time you invoke CodeView. Using Animate from the Run menu is not practical with applications that use forms. Since form application have an implicit DOEVENTS loop, the animation seems to "stick" at one instruction. Applications that rely on timers, such as CLOCK.FRM, may not update as expected when debugged in CodeView. ------------ 1.9 Overlays ------------ Calculating the Offset of Errors -------------------------------- If you are using the assembly listing generated when compiling with /A to debug an overlaid program, you must subtract the start address of the overlaid module from the offset in the error message to get the correct code offset. For example: Error Message: Division by zero in line 0 of WILMA as address 9FE9:0129 Excerpt of .MAP File Generated by LINK: Start Stop Length Name Class . . . Overlay 1H 00000H 00053H 00054H FRED_CODE BC_CODE 00060H 000B3H 00054H BARNEY_CODE BC_CODE 000C0H 00154H 00095H WILMA_CODE BC_CODE Overlay 2H . . . To calculate the actual error address, subtract the start address of the module WILMA (000C0H) from the offset given in the error message (0129): 129H - C0H = 69H The offset of the error is 0069 in the compiler assembly listing. CHAIN ----- You cannot use CHAIN in overlaid applications compiled without /O. This is because the run-time module is retained in memory across the CHAIN and a new overlay heap cannot be initialized. --------- 1.10 ISAM --------- Microsoft Windows ----------------- When using the ISAM TSRs (PROISAM.EXE, PROISAMD.EXE) in conjunction with Microsoft Windows, you must first start Windows and then load the ISAM TSR in an MS-DOS box. You cannot start Windows once the ISAM TSR has been loaded. MS-DOS version 3.10 ------------------- ISAM does not run under MS-DOS version 3.10. Opening a file for ISAM access results in a "Device I/O" error under that version MS-DOS. ------------- 1.11 BUILDRTM ------------- Removing ISAM and/or Forms Support ---------------------------------- Use the NOISAM.OBJ stub file to exclude ISAM support from your custom run-time modules. Use the NOFORMS.OBJ stub file to exclude forms support from your custom run-time module. In the standard run-time module, ISAM and forms features are loaded into memory at startup only if your application uses the feature. With a custom run-time module, these features are always loaded at startup, unless you use the stub files described above. LINK and BUILDRTM ----------------- BUILDRTM automatically invokes LINK with a /SEGMENTS option based on the number of objects and libraries being built. To manually set the /SEGMENTS option, set a LINK environment variable with the desired setting. Including Forms and Custom Controls ----------------------------------- You can include compiled form modules and custom controls in a custom run-time module. To access a form included in a custom run-time module, add a $FORM metacommand for the form to the module-level code of your application. ------------ 1.12 PROFILE ------------ The Microsoft Profiler cannot profile applications linked with /EX, which is the default when building an .EXE file from the programming environment. In order to profile an application, you must link it from the command line using the /CO linker option and omitting /EX. =========================================================================== Part 2: Corrections to "Microsoft Visual Basic Programmer's Guide" =========================================================================== Page Section\Note ---- ------------ xvii Sample Applications ------------------- REMLINE.MAK is not shipped with Visual Basic. SORTDEMO.MAK and TORUS.MAK are included in the Professional Edition only. The file for the SPIN custom control is SPINDEMO.*, not CUSTCTRL.*. 200 Table at Top of Page -------------------- "ir1_Click" should be "Dir1_Click". 490 Using Extended and Expanded Memory ---------------------------------- The last part of the second paragraph should read "and 0K of XMS for the programming environment." 497 Memory Map Table ---------------- As noted previously in this file, quoted string literals are stored in Far Heap, not Near Heap (DGROUP). 519 Language Summary, ALIAS Keyword ------------------------------- The ALIAS keyword is available in Visual Basic for Windows. 534 Language Summary, String Routines --------------------------------- All of the following string routines are available in Visual Basic for MS-DOS and are completely compatible with the Microsoft Basic Professional Development System: StringAddress, StringAssign, StringLength, StringRelease. 563 Drawing the Form ---------------- The illustration does not match the code that accompanies it. The text boxes should be labels and they should display different data. 564 Adding Code to Load the Form ---------------------------- The code that loads the form should be: CASE "B" frmSTUDENT.SHOW 1 =========================================================================== Part 3: Corrections to "Microsoft Visual Basic Reference" =========================================================================== Page Section\Note ---- ------------ iii Document Conventions -------------------- Keywords are shown in normal, uppercase in tables. Not bold. Keywords and literals are bold in syntax. 29 AutoRedraw Example ------------------ The third sentence that introduces the example should read "Print output on the form is retained when the form displays since AutoRedraw is True." It is important to set AutoRedraw to True if you want to display output printed to the form during the Load event. 34 BorderStyle Property -------------------- BorderStyle is read-only at run time for the forms and text box controls. It is read/write at run time for labels and picture boxes. BorderStyle 3 has Minimize and Maximize buttons. 123 DragDrop Event Syntax --------------------- Event procedure parameters (Source, X, Y, and Index) should not be bold. You may use any names for these parameters. The ones shown are provided automatically when you create an event procedure with the Edit Event Procedures dialog box. This applies to all event procedure syntax in the "Reference." 145 ERR Statement ------------- The value of n% cannot be >255. 170 FORMAT$ Function ---------------- The formating characters for fmt$ are omitted. See online Help for this information. 201 $INCLUDE Syntax --------------- The syntax for the $INCLUDE metacommand is as follows: {' | REM}$INCLUDE: 'filespec' 212 INPUTBOX$ Function ------------------ If prompt$ exceeds the length of a line, it automatically wraps to the next line. 251, LPRINT, PRINT, PRINT # 329, ---------------------- 330 You can't use the comma with the USING clause in any of these statements or methods. 259 Menu Control ------------ There is no DropDown event for menu controls. 273 MSGBOX Function --------------- The last line of example text should read: x% = MSGBOX(Msg$) 331 PRINT Statement --------------- The PRINT statement documentation is included under the LPRINT statment. 351 SCREEN Object ------------- AutoRedraw does not apply to the SCREEN object. 433 WRITE # Remarks --------------- The first paragraph indicates that using WRITE # to print to the screen causes an error if used with forms. It should state that this causes an error if forms are currently displayed. 440 Scan Code Table --------------- The scan code for decimal 78 is the gray "+" key, not "-" as shown. =========================================================================== Part 4: Corrections to Online Help =========================================================================== Creating a Control Array ------------------------ Steps 2 and 3 in this procedure are functionally redundant. Setting the Index property to 0 creates the control as an element of a control array, as does giving two controls the same CtlName property at design time. Save File As ------------ You can save forms in text format. Scan Code Table --------------- The table is missing these entries: Key Code --- ---- Esc 1 A 30 F1 59 AutoRedraw Property ------------------- This property does not apply to the SCREEN object. BorderStyle Property -------------------- BorderStyle is read-only at run time for the forms and text box controls. It is read/write at run time for labels and picture boxes. BorderStyle 3 has Minimize and Maximize buttons. ERR Statement ------------- The value of n% cannot be > 255. INPUTBOX$ Function Details -------------------------- If prompt$ exceeds the length of a line, it automatically wraps to the next line. Menu Control Details -------------------- There is no DropDown event for menu controls. SCREEN Object Summary --------------------- The AutoRedraw property does not apply to the SCREEN object. =========================================================================== Part 5: Corrections to "Microsoft Visual Basic Professional Features" =========================================================================== Page Section\Note ---- ------------ 31 Format of .DEF File ------------------- The placeholder segementname is the base name of the Basic source file plus the string "_CODE". For example, if a module is named NEW.BAS, the segmentname is "NEW_CODE". 271 SLN# Function ------------- The second bullet should be deleted.