Handling errors (only visual project type)

For a better and more precise control, you can handle errors at procedure level (or even at message level) with these two macros:

    StartErrorHandler (<Offset HandlerAddress>)

    EndErrorHandler

StartErrorHandler starts the error handling, specifying the address that will receive control when an error occurs, while EndErrorHandler specifies that the error handling ends its control. Yo can use these macros in the following way:

AnyProcedure Proc
    StartErrorHandler (Offset ErrorsPlace)
    code.....
Exit:
    EndErrorHandler
    Ret

ErrorsPlace:
    Cmp D[Error.Code], 0C0000005H ; Access violation read
    Jne < Exit
    do something
    Jmp < Exit
AnyProcedure EndP

This error handler will be active along all code between the two sentences (StartErrorHandler and EndErrorHandler), and any other procedures called inside it (unless those other procedures have their own error handler), until EndErrorHandler is reached (in the example aboce, at the end of the procedure). It is very important, for a correct behavior of the application, that each StartErrorHandler matches an EndErrorHandler at the same level (usually at the end of the procedure).

You can accurate even more the error handling. For example:

    Cmp D[uMsg], WM_CREATE
    Jne > L2
    StartErrorHandler (Offset ErrorsPlace1)
    code.....
    Jmp > Exit1

ErrorsPlace1:
    Cmp D[Error.Code], 0C0000005H ; Access violation read
    Jne > Exit1
    do something

Exit1:
    EndErrorHandler
    Jmp > End

L2:
    Cmp D[uMsg], WM_DESTROY
    Jne > Exit2
    StartErrorHandler (Offset ErrorsPlace2)
    code.....
    Jmp > Exit2

ErrorsPlace2:
    Cmp D[Error.Code], 0C0000005H ; Access violation read
    Jne > Exit2
    do something

Exit2:
    EndErrorHandler
End:
    Return (TRUE)

This type of handling works like Push and Pop. So, as said before, you should write an EndErrorHandler for each StartErrorHandler at the same level (take into account whether the procedure has two or more Ret o Return sentences due to the stack frame), so that it removes the handler address from the stack. If you do not do that, next time the program execution enters the procedure for processing any other message and an error occurs, it will not work properly.