This is an open source interpretation of what the MSVBVM60 library does. Such library is used in VB6 applications as a base-library, where most VB functions are implemented.

Well, there's no need to do this, but since VB6 is getting outdated, an open source runtime library might add some years to VB6's lifespan.

Since the source code of this library is not available, and reverse engineering the library is a no-go, we've used some tools to get the information we need. For instance, IDA was used against a dummy VB6 .exe file where the target function was called. API Monitor from ROHITAB was also used to check some runtime values and function calls from the original MSVBVM60.dll. Some reverse-engineering sites such as the ones listed in http://sandsprite.com/vb-reversing/

In order to contribute, please clone this repo, build it, and after you can run the example VB6 project, you can start adding new functionality. To do so, try to add a test in the dummy VB6 project and check if that doesn't work against this library. Normally these kind of errors are related to missing exported functions, so, it's easy to check what the original library did (using the methods described before). After the functionality is implemented, create a pull request.

You'll need Visual Studio 2026 to compile the MSVBVM60.DLL library. Just open the solution and build it (either Debug or Release).

An example VB6 project is located inside the Debug folder. In order to compile it, you'll need VB6 installed. Compile the .exe of that project inside the Debug folder, and run it from either opening it directly from Explorer, or from "Run" in Visual Studio (launch configuration will open the VB6 project, and you can add debug the library from there).

This library IS NOT A FULL replacement of the original library. So, don't expect to be a drop-in replacement.

Currently, a small subset of the original library are implemented. Most notable ones:

• Arrays
  • Internal functions (__vbaGenerateBoundsError, __vbaAryLock, __vbaAryUnlock, __vbaAryConstruct2, __vbaErase, __vbaAryDestruct) ✅
  • LBound (__vbaLbound) ✅
  • UBound (__vbaUbound) ✅
  • ReDim Preserve (__vbaRedimPreserve) ✅
  • ReDim (__vbaRedim) ✅
• Command Line
  • Command either for VARIANTARG or BSTR (rtcCommandBstr and rtcCommandVar) ✅
  • Setting the value of Command variable (rtcSetCommandLine) ✅
• Date and Time
  • Now (rtcGetPresentDate) ✅
  • Conversion from VARIANTARG to ``DATE` ✅
• • Exceptions
    • On Error Goto xxxx and On Error Resume Next statements are supported (vbaOnError) ✅
    • Err object not supported. ❌
    • Handling of the exceptions through SEH ✅
    • Growing and zeroing stack on functions prologue (__vbaChkStk) ✅
• File Interaction
  • All of these functions are wrapped in a class.
  • Open (__vbaFileOpen) ✅
  • Close (__vbaFileClose) ✅
  • LOF (rtcFileLength) ✅
  • Seek (__vbaFileSeek) ✅
  • Get (__vbaGet3) ✅
  • Put (__vbaPut3) ✅
• Floating Point
  • __adj_fdiv_m16i ❌ (stub)
  • __adj_fdiv_m32 ❌ (stub)
  • __adj_fdiv_m32i ❌ (stub)
  • __adj_fdiv_m64 ❌ (stub)
  • __adj_fdiv_r ❌ (stub)
  • __adj_fdivr_m16i ❌ (stub)
  • __adj_fdivr_m32 ❌ (stub)
  • __adj_fdivr_m32i ❌ (stub)
  • __adj_fdivr_m64 ❌ (stub)
  • __adj_fprem ❌ (stub)
  • __adj_fprem1 ❌ (stub)
  • __CIatan ❌ (stub)
  • __CIcos ❌ (stub)
  • __CIexp ❌ (stub)
  • __CIlog ❌ (stub)
  • __CIsin ❌ (stub)
  • __CIsqrt ❌ (stub)
  • __CItan ❌ (stub)
  • ___vbaCyMul ✅
  • __allmul ✅
  • ___vbaFpI2 ❌ (stub)
  • __vbaUI1I2 ✅
  • _adj_fptan ✅
  • _adj_fpatan ✅
• InputBox (rtcInputBox) ✅
• DLL function calls (DllFunctionCall) ✅
• Locale (getUserLocale) ✅
• MsgBox (rtcMsgBox) ✅
• Creation of COM objects
  • New <class> (__vbaNew) ✅
    • Regular classes can be instantiated, with private and public members, but events are NOT supported.
  • ActiveX objects CreateObject (rtcCreateObject2) ✅
  • Internal helpers for COM objects (__vbaObjSet, __vbaObjSetAddref, __vbaCastObj, __vbaObjVar, __vbaLateMemCall, __vbaVarLateMemCallLdRf, __vbaFreeObjList) ✅
  • __vbaVarLateMemCallLd ❌
  • Set obj = Norhing (__vbaFreeObj) ✅
  • Invocation of methods and properties of COM objects ✅
  • GetActiveObject with proper redirects for internal VB objects (VBGlobal, etc.) ✅
• Strings
• Variants
• Access to the VBA object's functions
  • Activate (rtcAppActivate) ✅
  • Beep (rtcBeep) ✅
  • Choose (rtcChoose) ✅
  • Environ (rtcEnviron) ✅
  • Iif (rtcImmediateIf) ✅
  • Partition (rtcPartition) ✅
  • SendKeys (rtcSendKeys) ❌ (TODO: use Karl E. Peterson's SendInput)
  • Shell (rtcShell) ✅
• VB global object
  • App member object
    • App.Path (get_Path) ✅
    • App.EXEName (get_EXEName) ✅
    • App.Title (get_Title) ✅
    • App.Major (get_Major) ✅
    • App.Minor (get_Minor) ✅
    • App.Revision (get_Revision) ✅
    • App.Comments (get_Comments) ✅
    • App.CompanyName (get_CompanyName) ✅
    • App.FileDescription (get_FileDescription) ✅
    • App.LegalCopyright (get_LegalCopyright) ✅
    • App.LegalTrademarks (get_LegalTrademarks) ✅
    • App.ProductName (get_ProductName) ✅
    • App.hInstance (get_hInstance) ✅
    • App.ThreadID (get_ThreadID) ✅
    • All other members are stubbed out ❌

Right now there's NO compatibility with applications that manipulate the internal MSVBVM60.DLL objects, like the ones obtained by calling TlsGetValue, or other undocumented APIs (at least at this time).