Importing a VB6 project

The IDE turns a VB6 project file, a .vbp, into a new twinBASIC project. The compiler does the conversion: it reads the .vbp and the files it names, and gives the IDE the settings and the files of a twinBASIC project. This page describes the routes, what the importer converts and what it leaves, the log it writes, and what to do next. The FAQ entries What does ‘100% backwards compatible’ mean and So some of my projects won’t work? say what to expect of VB6 code.

The routes

Route	What it does
New → Import from VBP… in the New / Open Project dialog, then Open or a double-click	Closes the open project, opens a Windows picker for the `.vbp`, then imports it. See the note on the import cards.
File → Open Project… (`Ctrl`+`O`), or Browse… in the dialog, with a `.vbp` chosen	The same import. A name that ends `.vbp` goes to the importer.
The Recent (VB6) section of the dialog	Loads the `.vbp` by another route, described below.
A `.vbp` on the command line	The same as Recent (VB6).
Project → Add → Import… with a `.vbp`	Is not a new project. It copies files of the VB6 project into the open project. See Single files and the Import tree.

The card Import from folder… is not a route for a VB6 project. It opens the folder of a twinBASIC project. See New Project.

The first two routes

The IDE sets the build configuration to win32, sets DEP off and large-address-aware on, and shows a progress indicator while the compiler converts the project. Then the New Project Options box opens, with the rows of an import:

Project Name, from the .vbp’s Name.
Option Explicit ON, ticked. The importer itself leaves the setting off, but the box starts ticked, so a default import ends with it on. A project that relies on undeclared variables then shows errors; see After the import.
Unicode Common Control Notifications, ticked.
Visual Styles, when the project has no manifest, and DPI Awareness, for a Standard EXE. The DPI choice starts at NONE.
Register to HKEY_LOCAL_MACHINE, ticked, for an ActiveX DLL or ActiveX Control. An IDE that is not running as administrator then shows a warning about the machine-wide registry once after Continue. See ActiveX registration.

There is no Include Common Controls row. New Project Options describes all the rows.

Continue opens the project. It is unsaved and marked as changed, it is named from the box, and the title bar reads Unsaved.twinproj. Nothing is written to disk until you save it: File → Save Project opens the Save As box. A failed import shows the box ERROR: LoadProject failed. Error code … and nothing else.

The other two routes

A .vbp loaded from Recent (VB6) or the command line shows no New Project Options box. It gets the importer’s own settings. Option Explicit is off, and the project has no visual-styles manifest. The project is not marked as changed, so its title bar has no dot. The build configuration box is left as it is. File → Save Project still opens Save As, closing asks nothing, and the .vbp file is not touched.

Use the first two routes when you want the box’s choices.

What the importer converts

Project settings

In the `.vbp`	In the new project
`Name`	the project name and the application title
`Type=Exe`, `Type=OleDll`, `Type=Control`	a Standard EXE, an ActiveX DLL or an ActiveX Control
`Startup`	the Startup Object: `Sub Main` or a form. An ActiveX DLL or Control gets `(None)`.
`IconForm`	the Icon Form
`LinkSwitches` with `/SUBSYSTEM:CONSOLE`	Is Console Application set to Yes. The switch must be in capitals. It may stand alone, under `[VBCompiler]`, or among other switches in quotes. In lower case, or as `/SUBSYSTEM:WINDOWS`, it sets nothing, and no other linker switch is carried over.
`Title`, `Description`, `MajorVer`, `MinorVer`, `RevisionVer`, `VersionCompanyName`, `VersionFileDescription`, `VersionLegalCopyright`, `VersionProductName`	the matching version settings
`AutoIncrementVer=1`	the version’s auto-increment, set to Revision
`Reference=`	a reference to the type library, with its path
`Object=`, such as `MSCOMCTL.OCX`	a COM reference to the control file, and support for ActiveX controls turned on

See Project Settings for these settings. The importer also adds the WinNativeForms package as a reference, turns Use Unicode Standard Library on, and sets the Build Output Path to a file in the project’s folder, such as ${SourcePath}\Project1.exe, not to the Build folder of the templates.

A reference to a type library the machine does not have fails to load, and Project Settings opens by itself on Library References. The version in the list can differ from the one the line names: a line for MSComctlLib that says 2.0 shows 2.1. To use the controls of an OCX, register it first; see the FAQ.

Files

A .bas or .cls file is copied unchanged, with its Attribute lines.
A .frm, .ctl or .pag file becomes two files. The designer file is Form1.frm.tbform, Ctl1.ctl.tbcontrol or Pag1.pag.tbppage. The code is in Form1.frm.twin, Ctl1.ctl.twin or Pag1.pag.twin, as a Class with the file’s code. An MDI form is converted the same way, and the startup object is the MDI form.
A UserControl’s list of property pages, which VB6 keeps in the .ctx file, goes into its .tbcontrol file.
A .frx file is read with its form. A picture or icon of the form’s controls is kept as bytes inside the .tbform, and the project gets no Resources entry for it. A .frx record that VB6 itself cannot read loses its picture without a message.

How the Attribute lines are kept, and which of them have an effect in a built ActiveX DLL, is in the FAQ.

Resources

A .res file named by ResFile32= is imported as the project’s resources, and the log says imported resource file. Its manifest becomes Resources\MANIFEST\#1.xml. A string table becomes Resources\STRING\Strings.json. A resource of a numeric type keeps its type and its id: RT_RCDATA with id 201 is Resources\RCDATA\#201, and a name stays a name. The FAQ lists the resource folders.

Warning BETA 1034

A resource whose type is a name, such as CUSTOM or MYDATA, is imported with an empty name. The folder Resources\<type> holds one blank row, however many resources of that type the .res file holds, and the log still reports 0 ERRORS/WARNINGS. A saved project keeps the bytes of each resource under an empty name, and the IDE shows the row as empty. A build then ends with NATIVE EXCEPTION: ACCESS_VIOLATION and makes no executable. Resources whose type is a number are right, RT_RCDATA included. Take the resources of a named type out of the .res file before the import, and add them to the project afterwards, as Resources describes.

What the importer leaves

The code. The importer does not change it. A .bas or .cls file is copied as it is, and the .twin file of a form holds the form’s code as VB6 wrote it. twinBASIC compiles it as VB code.
The Attribute lines. They stay as VB6 wrote them, and none becomes a twinBASIC attribute.
The linker switches other than /SUBSYSTEM:CONSOLE in capitals.
A .frm chosen alone with Project → Add → Import…, with no .vbp. It is copied unconverted.
The controls of an OCX. The importer adds the reference, and the OCX has to be registered on the machine.

The import log

The project gets a file Sources\__IMPORT_LOG.md. It lists what the importer did, one line for each file and setting. A few lines, as they read:

added project.reference 'OLE Automation'
imported module 'Module1.bas'
imported class 'Class1.cls'
imported usercontrol 'UserControl1.ctl'
imported propertypage 'PropertyPage1.pag'
imported resource file 'Project1.res'
imported form 'Form1.frm'

The lines for the settings come first, and the forms are logged last, whatever their line in the .vbp. The log ends with IMPORT FINISHED WITH n ERRORS/WARNINGS and the advice Please check the DIAGNOSTICS PANEL. After the import, the one tab that is open is a preview of this file.

The IDE after an import: the log in a preview tab, the imported files in the Project Explorer, and a dot in front of the name in the title bar.

A file that is missing

If the .vbp names a module, form, class, user control or resource file that is not there, the compiler opens a native Windows box. Its title is Error reading file., its text is the name of the file, and it has one OK. Meanwhile the IDE shows Migrating VBP to twinproj format… and Esc does nothing, so the IDE seems to hang. If the box is not in front, look for it in the taskbar. After OK the import goes on. The log then holds a line such as importing module 'Gone.bas' FAILED; unable to open or read the file, or import resource file 'Gone.res' FAILED, and ends with IMPORT FINISHED WITH 1 ERRORS/WARNINGS.

The Windows box for a missing file, its title cut off by the width of the box, with the file’s name and one button.

After the import

Save the project. It has no file yet: File → Save Project opens Save As. See A project with no file.
Read the DIAGNOSTICS panel. The errors are usually Unrecognized symbol (TB5079) for variables that were never declared, because Option Explicit ON was left ticked. Either untick the row in the box, or set Option Explicit On to No in Project Settings. The warning TB0002 can be set to IGNORE. The FAQ shows both.
Run it. Start (F5) runs the project in the compiler. See Running.

Single files and the Import tree

Project → Add → Import… imports files into the open project, not a new project. See Import. Three cases:

A .bas or .cls file is copied as it is.
A .frm chosen alone is copied unconverted, as Sources\Form1.frm, with its text. Its .frx is not copied. No box opens, and the project is saved.
A .vbp opens the Import from twinproj… tree, with the files already converted. The first row shows the project’s name and path; below it come the Resources, Sources and Miscellaneous branches. Tick both files of a form, Form1.frm.tbform and Form1.frm.twin. A user control and a property page have two files each, in the same way, and the log is a file too. Import copies the ticked files into the open project.

The Import from twinproj dialog: a tick-box tree of everything found in a VB6 project, with the Resources and Sources branches open. The two files of a form are both ticked.