Error System

Source: source/function/errsysw.prg

FiveWin replaces Harbour's default error handler with a GUI-based error dialog that displays detailed diagnostic information. The error system is automatically initialized at application startup via the ErrorSys() procedure, which sets an error block calling ErrorDialog().

Error Handling Flow

flowchart TD A[Runtime Error Occurs] --> B{Error Type?} B -->|Division by Zero| C[Return 0
silently] B -->|Network Open Error| D[Set NetErr .T.
Return .F.] B -->|Append Lock Error| E[Set NetErr .T.
Return .F.] B -->|Other Error| F[ErrorDialog] F --> G[Build Error Log] G --> H{bUserDlg set?} H -->|Yes| I[Call Custom Dialog] H -->|No| J[Show FWH Error Dialog] J --> K[User Chooses Action] K -->|Quit| L[Write error.log
QUIT] K -->|Retry| M[Return .T.] K -->|Default| N[Return .F.] K -->|Debug| O[AltD at error] L --> P{bUserAction set?} P -->|Yes| Q[Execute Post-Error Action] P -->|No| R[Application Exits]

Automatic Error Handling

Certain error types are handled automatically without showing the error dialog:

Error	genCode	Automatic Action
Division by zero	`EG_ZERODIV`	Returns 0 silently
Network open error (OS code 32 or 5)	`EG_OPEN`	Sets `NetErr(.T.)`, returns .F.
Append lock error	`EG_APPENDLOCK`	Sets `NetErr(.T.)`, returns .F.
Recursive error (7+ levels deep)	any	Forces QUIT to prevent infinite loop

Error Dialog

The FiveWin error dialog is a modern, feature-rich dialog that adapts to the system theme:

Dark mode auto-detection -- the dialog reads the Windows "AppsUseLightTheme" registry key and adjusts its color scheme accordingly
Error message -- displayed prominently at the top
Call stack -- shown in a listbox with procedure names, line numbers, and source files
Action buttons:
- Quit -- writes error.log and terminates
- Retry -- returns .T. (if e:canRetry)
- Default -- returns .F. (if e:canDefault)
- Debug -- activates the debugger (if available)
Copy button -- copies the complete error log to the clipboard
See button -- opens error.log in Notepad

Error Log Format

When the user clicks "Quit", an error.log file is written (or appended). The log contains these sections:

Application
===========
   Path and name: C:\myapp\myapp.exe (32 bits)
   FiveWin version: FWH 26.05
   Harbour version: 3.2.0
   Date: 2026-03-24
   Time: 14:30:45

Error
=====
   Description: Argument error
   SubSystem: BASE
   Operation: +
   Args:
      [1] = C "Hello"
      [2] = N 42

Call Stack
==========
   Called from MAIN(25) in source\main.prg
   Called from PROCESSDATA(102) in source\process.prg
   ...

System
======
   OS: Windows 11 Build 22621
   Windows Directories
   Active tasks

Databases in use
================
   Area 1: CUSTOMERS (customers.dbf) RecNo: 42 RecCount: 1500
   ...

Customizing the Error System

SetErrorPath() / SetErrorFileName()

// Change error log location
SetErrorPath( "C:\logs\" )
SetErrorFileName( "myapp_error.log" )

SetErrorDialog() -- Custom Dialog

// Replace the entire error dialog with a custom one
SetErrorDialog( { |oDlg, e, cLog, aStack|
   // oDlg is the dialog being created
   // e is the error object
   // cLog is the error log text
   // aStack is the call stack array
   // Return: nil (use default buttons) or handle buttons yourself
} )

SetPostErrorAction() -- Post-Error Hook

// Execute code after the error dialog closes
SetPostErrorAction( { |e, cLog|
   // Send error report to server
   SendErrorReport( cLog )
   // or restart the application
   // WinExec( GetModuleFileName( GetInstance() ) )
} )

Custom ErrorBlock

// Replace the error handler entirely
ErrorBlock( { |e| MyErrorHandler( e ) } )

static function MyErrorHandler( e )

   // Log to file
   LogFile( "errors.log", { e:Description, e:Operation, ;
      ProcName(4), ProcLine(4) } )

   // Show simple message
   MsgStop( e:Description + CRLF + ;
      "at " + ProcName(4) + "(" + LTrim( Str( ProcLine(4) ) ) + ")" )

   // Quit the application
   PostQuitMessage( 0 )
   __Quit()

return nil

Example: TRY/CATCH Blocks

#include "FiveWin.ch"

function Main()

   local xResult

   // TRY/CATCH prevents the error dialog from showing
   TRY
      xResult := SomeRiskyOperation()
      MsgInfo( "Result: " + cValToChar( xResult ) )
   CATCH e
      MsgAlert( "Error: " + e:Description + CRLF + ;
         "Operation: " + e:Operation )
   END

return nil

Example: Custom Error Handler with Email

#include "FiveWin.ch"

function Main()

   // Install custom post-error action
   SetPostErrorAction( { |e, cLog|
      // Save error log
      MemoWrit( "crash_" + DToS( Date() ) + "_" + StrTran( Time(), ":", "" ) + ".log", cLog )

      // Could send email notification here
      // SendMail( "admin@company.com", "App Crash", cLog )
   } )

   // Change error log location
   SetErrorPath( "C:\logs\" )
   SetErrorFileName( "app_errors.log" )

   // ... rest of application ...
   AppMain()

return nil

Error Object Properties

The error object e passed to the error handler is a standard Harbour Error object:

Property	Type	Description
`e:Description`	Character	Human-readable error description
`e:Operation`	Character	The operation that caused the error
`e:SubSystem`	Character	Subsystem name (BASE, DBCMD, etc.)
`e:genCode`	Numeric	Generic error code (EG_*)
`e:subCode`	Numeric	Subsystem-specific error code
`e:osCode`	Numeric	Operating system error code
`e:Args`	Array	Arguments that caused the error
`e:canRetry`	Logical	Whether retry is possible
`e:canDefault`	Logical	Whether default action is possible
`e:canSubstitute`	Logical	Whether a substitute value can be returned
`e:FileName`	Character	File that caused the error (if applicable)

Multi-Language Support

The error dialog uses FWString() for all user-visible text, so it automatically adapts to the language set by FWSetLanguage(). Supported strings include "Application", "Path and name", "Date", "Time", error descriptions, and button labels.