Mid statement
Posted: Wed Oct 30, 2013 7:01 pm
A number of PB users have complained about the lack of certain statements in PB that are common to other BASIC dialects. When we first started using PB, we spent a few months creating macros and support procedures to replicate, as much as possible, the standard BASIC syntax. We also included many macros to implement some useful PowerBasic statements, such as StrPtr, to make it easier to do the conversion.
So for those like myself, who migrated to PB from PowerBasic, here's a simple solution for the Mid statement. It uses macros, in conjunction with a procedure, to hide the quirky PB syntax and to avoid PB's messy ByRef "feature". We didn't include PowerBasic's ability to do reverse text substitutions, by means of negative lengths, but this would be easy to add if needed.
To be consistent with our naming conventions, we implemented the Mid-function and Mid-statement as MidGet and MidSet.
So for those like myself, who migrated to PB from PowerBasic, here's a simple solution for the Mid statement. It uses macros, in conjunction with a procedure, to hide the quirky PB syntax and to avoid PB's messy ByRef "feature". We didn't include PowerBasic's ability to do reverse text substitutions, by means of negative lengths, but this would be easy to add if needed.
To be consistent with our naming conventions, we implemented the Mid-function and Mid-statement as MidGet and MidSet.
Code: Select all
Macro StrPtr (bvsString)
@bvsString
EndMacro
Macro MidGet (bvsString, bviPosn, bviLength)
Mid(bvsString, bviPosn, bviLength)
EndMacro
Macro MidSet (bvsString1, bviPosn, bviLen2, bvsString2)
subMidSet (StrPtr(bvsString1), Len(bvsString1), bviPosn, bviLen2, bvsString2, Len(bvsString2))
EndMacro
Procedure subMidSet (bviStringPtr1.i, bviLength1.i, bviPosn.i, bviLen2.i, bvsString2.s, bviLength2.i)
Protected iLength1.i ; calculated new length of string1, before truncation to its original length
Protected iLen2.i ; the number of characters to copy from string2 to string1
Protected iStringPtr1.i ; address in string1 that receives the copied characters
If bviLength1 < 1 Or bviLen2 < 1 Or bviLength2 < 1 Or bviPosn > bviLength1
ProcedureReturn ; no characters need to be copied
EndIf
If bviLen2 < bviLength2 ; select the fewest number of characters to be copied
iLen2 = bviLen2
Else
iLen2 = bviLength2
EndIf
iLength1 = bviPosn + iLen2 - 1 ; calculate the new length of string1
If iLength1 > bviLength1
iLen2 = iLen2 - (iLength1 - bviLength1) ; reduce the number of copied characters to fit into string1
EndIf
iStringPtr1 = bviStringPtr1 + bviPosn - 1
CopyMemory(StrPtr(bvsString2), iStringPtr1, iLen2)
EndProcedure
Define Text.s = "Hello World"
MidSet(Text, 9, 10, "12345") ; this requests that 10 characters be copied from "12345", starting at position 9 in Text
Debug Text ; Text = "Hello Wo123"
Define Text.s = "Hello World"
MidSet(Text, 1, 5, MidGet(Text, 7, 5))
Debug Text ; Text = "World World"