OS/2 Shareware BBS: 10 Tools/10-Tools.zip/vp11demo.zip/vpbase.rar/doc/FAQ.TXT

Text File | 1996-10-08 | 17KB | 431 lines

  Virtual Pascal for OS/2 v1.10
  Frequently Asked Questions
  (C) 1996 fPrint UK Ltd


  The answers to many of these questions can be found in the printed
  manual too.

Q: When I write a program, any "read" and "write" statements are syntax
   highlighted along with reserved words.  Why?

A: In the new object model, available in the {$Delphi+} state, Read and
   Write are standard directives used in property definitions.  A future
   version of VP/2 will allow you to specify separate colours for
   standard directives and reserved words.


Q: I am not able to generate any PM programs! The program compiles and
   links OK, but the executable is not a PM program. Am I doing
   something wrong?

A: You have to specify the application type to be PM application
   (Options|Linker|Application radio buttons).  Alternatively, you can
   specify the {$PMTYPE Parm} directive to set the application type.


Q: I have just created a Presentation Manager application, and I want to
   debug it using Virtual Pascal.  Once I get past the point where the
   message queue is created, the system hangs!  What do I do wrong?

A: OS/2 Presentation Manager programs can only be debugged safely if you
   run Virtual Pascal in a Full Screen session or if you run VP/PM.  VP/Txt
   in a window on the desktop should be used to debug text-mode applications
   only.


Q: The clock PM apps compiles and runs fine, but the PM game triplex compiles,
   but does nothing. It's there as a process but there is no window.

A: The compiler is not able to find the resource files required by the
   application. You have either to change to the directory where your
   resource file is located or include this directory into
   Options|Directories|Resource directories input box. Also check the
   messages in the Messages window.
   Compilation should include the following stages:
   Compiling...
   Linking...
   Compiling resources... (if there is no binary resource file or the resource
                           script file is newer than the binary resource)
   Binding resources...   (if binary resource file is found)
   Success.


Q: How can I make VP to compile and add resources to my program? In BP7
   under Windows I use the {$R filename.res} directive.

A: You can use the $R statement in VP as well.  Make sure that the
   .RES file in question is available in either the current directory
   or in a directory listed in the Options|Directories|Resource Dirs
   entry field.


Q1: I want to port a UI unit I wrote using Turbo Pascal to VP. In it I
    need to write directly to the screen. How can I do this in VP?

Q2: VP does not compile "absolute $B800:$0000" for video memory. I tried
    defining the addresses through variables, but then I receive a RUNTIME
    error #216.

A:  Absolute memory addresses have no meaning in protected mode, so they
    are not supported. You can use the following code to obtain a pointer
    to the logical screen buffer, write something to it and then show
    its contents.

===Cut===

{ Fills entire screen with character 'A' }

uses Os2Base, Use32;

type
  PScreenBuffer = ^TScreenBuffer;
  TScreenBuffer = array [0..7999] of record
    Ch:   Char;
    Attr: Byte;
  end;

var
  I: Integer;
  BufSize: SmallWord;
  ScreenBuffer: Pointer;
begin
  VioGetBuf(ScreenBuffer, BufSize, 0);   { Get logical screen buffer address }
  SelToFlat(ScreenBuffer);               { Convert it from selector:offset form to flat }
  for I := 0 to BufSize div 2 - 1 do
    with PScreenBuffer(ScreenBuffer)^[I] do
    begin
      Ch := 'A';        { 'A' }
      Attr := $4F;      { White on red }
    end;
  VioShowBuf(0,        { Buffer offset }
             BufSize,  { Length in bytes to show }
             0);       { Vio handle - should be 0 for text mode apps }
end.
===Cut===

Q: The following code brings up the error-message: Error 26: Type mismatch

uses Dos;
  var Year,Month,Day,DayOfWeek: Word;
begin
  GetDate(Year,Month,Day,DayOfWeek);
end.

A: You have to include the Use32 unit in uses of each unit. Please refer
   to the manual for details.


Q: The Delay function from the Crt unit seems does not work correctly if
   values less then 150 are specified.

A: The OS/2 system timer interval is 31ms, which is why it is not
   possible to make a delay less than this value using the OS/2 API.
   VP/2 uses a special routine for small time intervals to make small
   delays. Unfortunately, even this routine cannot be exact in a
   multi-tasking environment like OS/2.


Q: Ctrl-F2 in BP is like Shift-F4 in VP/2; why not make it the same ?

A: The are not quite the same. Since the VP/2 IDE includes some features
   from the standalone debugger, there are 2 functions: Ctrl-F2 and
   Shift-F4.
   Ctrl-F2 - Restart program - is the same as the Turbo Debugger Reset
   program. You should use it to restart a debugging session, and debug
   your program once more.  You can also use it to load a just compiled
   program (BP does not have this feature at all).
   Shift-F4 is like Reset Program in BP, but you are not able to
   run/debug your program without recompilation, since it terminates
   the debugging session and frees the debug information.


Q: In the integrated debugger, even after termination of the program,
   the session with program output is still available and debugging
   process is still present in the task list. How can I get rid of it?

A: After termination of the program, you still can examine the value of
   static variables (typed constant and global variables) and see the
   program's screen output. You can use the Run|Reset program command
   (Shift-F4) to terminate the debugging session and free the debug
   information. It also deletes the screen session of the debugging
   program. However, having done so, further debugging is not possible
   unless you recompile the program.


Q: Even though the source is compiled, if I load program I can not step
   through the source (The assembler window takes focus). What happens?

A: You have to enable {$D+} (Options|Compiler|Debug information is checked).


Q: Unlike BP, the value of the iteration index becomes 1 more than the
   number of iterations in FOR loop. For example:

        for I := 1 to 4 do;

   at this point VP says I = 5 whereas TP says I = 4.
   Is there something wrong?

A: No, VP generates different code for FOR loops. The value of the FOR
   control variable is not defined by the language and depends on
   different implementations of the compiler. You should not rely on
   the value of the FOR control variable outside the loop body.


Q: Since VP is a 32-bit compiler and has no 64K restriction on size of
   the variables, I tried to compile a little program like this:

===Cut===
var
  HugeVar: array[0..32*1024*1024] of Byte;
begin
  FillChar(HugeVar, SizeOf(HugeVar), 'A');
end.
===Cut===
   but receive the following message from LINK386:
   LINK386 :  fatal error L1204

A: Use the built-in linker of VP/2 instead of LINK386.  The built-in linker
   does not have the restrictions imposed by LINK386.


Q: When I compile code containing "DosError", the compiler reports an
   error saying something resembling, "Error: '(' expected" after the
   "DosError" variable, as if it expected arguments, like in a procedure
   call. To work around this, I replaced "DosError" with "Dos.DosError"
   to direct VP to the DOS unit. It compiled successfully this way. Any
   idea why? Should I be using "DosError" in a special way?

A: OS/2 has function named DosError, defined in the Os2Base unit.
   Thus, if the Dos unit is included before Os2Base in your Uses clause,
   the DosError function from Os2Base unit is found before the Dos unit
   variable. You have either to put the Dos unit after Os2Base in the
   uses clause or use a fully qualified identifier - the latter being
   the recommended way of resolving the problem.


Q: I use the following code fragment to search for files, but it never
   returns the volume label.  Am I doing something wrong?
===Cut===
   FindFirst('*.*', $3F, SR);
===Cut==

A: The volume label is not returned by the OS/2 version of FindFirst.  If
   you want to query the volume label, you need to use the DosQueryFSInfo
   API call:
===Cut===
   Uses Use32, Os2Def, Os2Base;
   Var
     DriveNumber : Word;
     Buf : Record
       SerialNum : Word;
       VolLabel  : String;
     end;
   Begin
     DriveNumber := 3;  { Drive C }
     DosQueryFSInfo( DriveNumber, fsil_VolSer, Buf, Sizeof( Buf ));
   End;
===Cut===


Q: The ChDir standard procedure does not work correctly. If I change my
   directory in a program and leave the program I find the working
   directory unaltered. What is wrong?

A: OS/2 maintains a current directory for each process. If you change
   the current directory in your program, it does not affect the current
   directory of the parent process (usually CMD.EXE which is used to run
   your program). That is why when your program terminates, the current
   directory remains the same as it was before running it.


Q: I have noticed that PathStr have changed from String[79] in BP to
   String. DirStr, NameStr and ExtStr have changed too. Is there a
   reason for that?

A: Yes, VP supports HPFS long file names of the OS/2. The length of each
   path component can be up to 255 characters long. That is why PathStr
   and other types in Dos unit have been extended to String type. The
   File and Text variables have been expanded accordingly to hold long
   file names (cf the FileRec and TextRec types in Dos unit).


Q: I can not declare a variable of the important type REGISTERS.
   Please give me a hint.

A: Neither MsDos or Intr from Borland Pascal are supported.
   OS/2 application have no access to the BIOS/DOS API like BIOS/DOS
   interrupts, DPMI, etc. OS/2 performs all file I/O, video and memory
   management tasks itself.
   The only way to support these functions is to emulate all DOS API
   using the OS/2 API which is almost impossible to do. Instead of using
   DOS and BIOS calls you should use base OS/2 API calls, defined in
   the Os2Base unit or make use of the interface functions provided in
   the VPUtils unit.


Q: What should I do with my 16-bit inline assembler codes?

A: Since 16-bit inline codes should be rewritten as 32-bit code,
   you have two alternatives:
     - replace the offending inline statement with an ASM ... END statement;
     - use inline functions/procedures that can be written in Pascal
       (cf inline procedural directive, see the manual for details).


Q: I have just got some strange test results with the MaxAvail and
   MemAvail functions. Normally MaxAvail <= MemAvail, but in some
   cases MemAvail > MaxAvail...?

A: MemAvail and MaxAvail gives you only rough estimates of the remaining
   memory, since system conditions change constantly in a multitasking
   environment. Your results just means that another process (or the
   system itself) has allocated (or freed) some memory between the calls
   to MemAvail and MaxAvail.


Q: With MemAvail being unreliable, is there a way of accurately finding
   out if my program suffers from a memory loss because I forget to
   free some dynamically allocated memory?

A: Yes; the MemUsed function in VPUtils returns the number of bytes
   currently allocated on the heap.


Q: In many of my old programs, I return $FFFF in a Word variable to
   signal "failure" or "not found".  In Virtual Pascal, a Word is 32 bit so
   my test fails.  What should I do to make the code work with both BP7
   and VP/2?

A: Typecast -1 to Word and compare with this value.  In VP, Word(-1) is
   $FFFFFFFF, and in BP, Word(-1) is $FFFF.  For your comparison to work
   in both Borland and Virtual Pascal, it should be
===Cut===
   If Test <> Word(-1) then
     Writeln('Found');
===Cut===


Q: VP.EXE starts from both DOS and OS/2 tasks, and never gives an error
   saying "This program requires OS/2".  This is nice, and I want my
   programs to do the same!  How?

A: Any program linked with the built-in linker of VP/2 will behave in this way.


Q: I have defined a PM dialog, that requires a function of type FnWp as
   a parameter.  I have defined a function of this type, and specify
   the name of the function in the WinDlgBox call.
   When I compile, I get a "Type Conflict" error.  Why?

A: Provided the function header is correct, and matches the definition
   in Os2PmApi, you probably use the wrong calling convention.  This
   procedure needs to be called by OS/2, and needs to use the C-style
   calling convention.  Adding the cdecl; procedural directive after the
   function definition will probably make it work.


Q: I wish to save the current directory when I save my desktop settings,
   just like in Borland Pascal.  How do I do this?

A: Check the "Return to last dir" checkbox in the
   Options|Environment|Preferences dialog.


Q: I have written multithreaded programs using the Beta or EEP version of
   VP/2, and the BeginThread calls do not compile anymore.  What has changed?

A: The BeginThread function has changed to take the same parameters as
   in Borland Delphi v2.  This means, that the thread function should be
   declared as
     Function ThreadFunc( P : Pointer ) : Longint;
   In addition to this change, a number of extra parameters are required.
   If you just want to start a thread and use a set of default values that
   normally make sense, you can use VPUtils.VPBeginThread.


Q: I have enabled Smart Linking to prevent unused functions from taking up
   space in my executable.  If I look at the output file, not all of them
   are removed!  Why?  How can I make this work?

A: This requires a bit of explanation:
   The first step of Smart Linking in VP/2 takes place at compile time.
   When Smart Linking is disabled, the compiler generates one object
   module (which is stored in an .OBJ file) per unit and these modules
   are then linked to form the executable.
   When Smart Linking is enabled, one object module per procedure, function
   and typed constant is generated and the result is stored in a .LIB file.
   At link time, only those object modules required by the application are
   linked into the executable.
   To link the executable, the linker needs the main file to be an OBJ file,
   however.  Thus, any functions defined in the main program file are not
   smart linked away.
   If this is a problem, the solution is to have an "empty" main program,
   that only uses one unit and calls the main function of that unit as its
   only action.


Q: I have a program that uses the new SysUtils unit. When an exception
   occurs, a big red screen pops up!  What is wrong?

A: When an exception causes the program to terminate, the termination
   routines can either display the message in Grey on Black as it happens
   for run-time errors, or it can display the message in a full-screen
   window to prevent the user screen from being corrupted by the error
   message.  The default is the last approach; you can change this behaviour
   by setting
     PopupErrors := False;


Q: I have enabled Exception Location Information in all units, but my
   program crashes without displaying line number information.  Why?

A1:Only units compiled in the {$D+,LocInfo+} state will have location
   information available.  If you program crashes in a unit not compiled
   in this state, for example the System unit, no ELI will be displayed.

A2:Remember to check the Options|Linker|Generate Location Info checkbox
   in the Options|Linker dialog.


Q: I have found the OS/2 .SYM files on the OS/2 CD-ROM; how do I make use
   of these in VP/2's debugger?

A: Specify the directory containing the files as a parameter to VP. For
   example, if some of the files are in C:\VP11\SYM and some in D:\SYM,
   start VPPM.EXE with
     VPPM.EXE /sC:\VP11\SYM;D:\SYM
   or change the Parameters section in the settings/proprties for the VP
   program objects on the desktop.


Q: The compiler complains that my $LINKER statement is invalid, though I
   have checked that all the keywords are valid.  Why?

A: All statements in a $LINKER statement (or .DEF file) are case sensitive
   and must be entered in upper case.


Q: How do I determine what type of disk is associated with a particular
   drive letter?

A: Call the GetDriveType function of the VPUtils unit with the drive
   letter as the parameter.  This function returns one of the following
   enumerated values:
     dtFloppy    - Floppy disk
     dtHDFAT     - FAT Hard Disk Drive
     dtHDHPFS    - HPFS Hard Disk Drive
     dtInvalid   - Invalid drive
     dtNovellNet - Novell Net drive
     dtCDRom     - CD ROM drive
     dtLAN       - LAN drive


Q: I would like to get a list of all valid drive letters on a system. How?

A: The GetValidDrives procedure in the VPUtils unit returns a set
   containing all valid drive letters.