Go to LB Isam Introduction or to the LB Isam Demonstration Code
LB ISAM Function Library
'lbisam.bas
'-------------------------------------------------------------------------------
'function initfunclib
' use once in your program before using any of the functions in this library
' does some initialisations
'-------------------------------------------------------------------------------
Function initfunclib()
Dim globalinf$(10)
End Function
'-------------------------------------------------------------------------------
'function getcount
' used to get the number of records in the index
' parameters passed
' indexname$ = name of indexfile
' keylength = length of key
' returns nr of records in the index
'------------------------------------------
Function getcount(indexname$,keylength)
Open indexname$ For Binary As #oi9
'get nr of records
qtyBytes = Lof(#oi9)
getcount=qtyBytes/(5+keylength)
Close #oi9
End Function
'-------------------------------------------------------------------------------
'function index
' used to create an index on a file with fixed recordlengths (random or binary)
' the max number of records = 99999
' parameters to be passed:
' filename$ = filename of file to be indexed
' reclen = recordlength
' indexname$= name of the indexfile to be created
' keybegin = the position in the record where the key begins
' keylength = length of the key
' unique = 0 = duplicate records allowed / 1 = no duplicates allowed
'the function returns the number of records indexed
'-------------------------------------------------------------------------------
Function index(filename$,reclen,indexname$,keybegin,keylength,unique)
Open indexname$ For Binary As #2
If Lof(#2)> 0 Then ' file already exists
Confirm "Indexfile already exists - do you want to replace it?"; answer$
If answer$="yes" Then
Close #2:Kill indexname$
Else
index=0:Close #2:GoTo [fin]
End If
Else
Close #2
End If
Open filename$ For Binary As #1
'get nr of records
qtyBytes = Lof(#1)
nrrec=qtyBytes/reclen
Dim rep$(10,2):ReDim rep$(nrrec+10,2)
top=0
For i=1 to nrrec
pointer=(i-1)*reclen
Seek #1,pointer
var$=Input$(#1,reclen)
x$=Str$(i):length=Len(x$)
For j=1 to 5-length
x$="0"+x$ 'pad with zeroes till len=5
Next j
rep$(i,1)=Mid$(var$,keybegin,keylength):rep$(i,2)=x$:top=top+1
Next i
Sort rep$(),1,top,1
' test for duplicates if unique=1
If unique=1 Then
For j=1 to top-1
If rep$(j+1,1)=rep$(j,1) Then
Notice"No duplicate keys allowed!!"
index=0
Close #1
GoTo [fin]
End If
Next
End If
' writeindex
Open indexname$ For Binary As #2
indrl=keylength+5 'reclen of index rec
For i = 1 to top
pointer=(i-1)*indrl
tot$=rep$(i,1)+rep$(i,2)
Print #2,tot$
Next i
index=nrrec 'ok
Close #1
Close #2
[fin]
ReDim rep$(10,2)
End Function
'-------------------------------------------------------------------------------
'function getkey
' used to search a key in an index
' parameters to be passed:
'
' indexname$= name of the indexfile to be searched
' keylength = length of the key
' key$ = key to search for
'the function returns the recordnr in the masterfile of the found key or if not found
'the negative recordnr after which it should have been if present
'-------------------------------------------------------------------------------
Function getkey(indexname$,keylength,skey$)
Open indexname$ For Binary As #oi1
'get nr of records
qtyBytes = Lof(#oi1)
nrrec=qtyBytes/(5+keylength)
l=1:u=nrrec+1
'---------------------------
[search]
flag=0
i=Int((l+u)/2)
pointer =(i-1)*(5+keylength)
Seek #oi1,pointer
key$=Input$(#oi1,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
If key$=skey$ Then
' found !!
' look for 1st corresponding key if non unique index
If i>1 Then
For j=i to 1 step -1
pointer =(j-1)*(5+keylength)
Seek #oi1,pointer
key$=Input$(#oi1,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
If key$ <> skey$ Then
getkey=j+1
Exit For
End If
Next j
Else
getkey=1
End If
GoTo [ret]
End If
If key$skey$ Then
If flag=0 Then volg=i:flag=1
If u=i Then
'Print"not found - previous is: ";volg
'Print" - next is: ";volg-1
getkey=vorige *(-1)
GoTo [ret]
Else
u=i
GoTo [search]
End If
End If
'------------------------------------
[ret]
If getkey>0 Then
pointer =(getkey-1)*(5+keylength)
Seek #oi1,pointer
key$=Input$(#oi1,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
globalinf$(1)=indexname$
globalinf$(2)=Str$(getkey)
globalinf$(3)=adress$
globalinf$(4)=key$
getkey=adress
Else
globalinf$(2)=Str$(getkey) 'returns neg pos after wich it should come
globalinf$(3)="0"
globalinf$(4)="NOT FOUND"
End If
Close #oi1
End Function
'-------------------------------------------------------------------------------
'function lookup
' used to search part of a key in an index
' parameters to be passed:
'
' indexname$= name of the indexfile to be searched
' keylength = length of the key
' key$ = key to search for
'the function returns the recordnr in the referencefile of the 1st found key
' or if not found the negative recordnr after which it should have been if present
'-------------------------------------------------------------------------------
Function lookup(indexname$,keylength,skey$)
Open indexname$ For Binary As #oi1
'get nr of records
qtyBytes = Lof(#oi1)
nrrec=qtyBytes/(5+keylength)
l=1:u=nrrec+1
'---------------------------
[search]
flag=0
i=Int((l+u)/2)
pointer =(i-1)*(5+keylength)
Seek #oi1,pointer
key$=Input$(#oi1,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
If Left$(key$,Len(skey$))=skey$ Then
' found
' look for 1st corresponding key
If i > 1 Then
For j=i to 1 step -1
pointer =(j-1)*(5+keylength)
Seek #oi1,pointer
key$=Input$(#oi1,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
If Left$(key$,Len(skey$))<> skey$ Then
lookup=j+1
Exit For
End If
If j=1 Then lookup=1
Next j
Else
lookup=1
End If
GoTo [ret]
End If
If key$skey$ Then
If flag=0 Then volg=i:flag=1
If u=i Then
'Print"not found - previous is: ";volg
'Print" - next is: ";volg-1
lookup=vorige *(-1)
GoTo [ret]
Else
u=i
GoTo [search]
End If
End If
'------------------------------------
[ret]
If lookup>0 Then
pointer =(lookup-1)*(5+keylength)
Seek #oi1,pointer
key$=Input$(#oi1,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
globalinf$(1)=indexname$
globalinf$(2)=Str$(lookup)
globalinf$(3)=adress$
globalinf$(4)=key$
lookup=adress
Else
globalinf$(2)=Str$(lookup) 'returns neg pos after wich it should come
globalinf$(3)="0"
globalinf$(4)="NOT FOUND"
End If
Close #oi1
End Function
'-------------------------------------------------------------------------------
' function getfirst
'searches For the first key in the index
'with Name=indexname and keylength=keylength
' returns recordnr of record in masterfile
Function getfirst(indexname$,keylength)
Open indexname$ For Binary As #oi9
i=1
pointer =(i-1)*(5+keylength)
Seek #oi9,pointer
key$=Input$(#oi9,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
getfirst=adress
globalinf$(1)=indexname$
globalinf$(2)=Str$(i)
globalinf$(3)=adress$
globalinf$(4)=key$
Close #oi9
End Function
'-------------------------------------------------------------------------------
' function getlast
'searches For the last key in the index
'with Name=indexname and keylength=keylength
' returns recordnr of record in masterfile
Function getlast(indexname$,keylength)
Open indexname$ For Binary As #oi9
'get nr of records
qtyBytes = Lof(#oi9)
i=qtyBytes/(5+keylength)
pointer =(i-1)*(5+keylength)
Seek #oi9,pointer
key$=Input$(#oi9,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
getlast=adress
globalinf$(1)=indexname$
globalinf$(2)=Str$(i)
globalinf$(3)=adress$
globalinf$(4)=key$
Close #oi9
End Function
'-------------------------------------------------------------------------------
' function getnext
'searches For the next key in the index from present position in globalinf$(2)
'with Name=indexname and keylength=keylength
' returns position in masterfile of next
Function getnext(indexname$,keylength)
Open indexname$ For Binary As #oi9
'get nr of records
qtyBytes = Lof(#oi9)
nrrec=qtyBytes/(5+keylength)
i=Val(globalinf$(2))+1
If i>nrrec Then
Notice"eof reached"
i=0:getnext=0
Else
pointer =(i-1)*(5+keylength)
Seek #oi9,pointer
key$=Input$(#oi9,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
getnext=adress
globalinf$(1)=indexname$
globalinf$(2)=Str$(i)
globalinf$(3)=adress$
globalinf$(4)=key$
End If
Close #oi9
End Function
'-------------------------------------------------------------------------------
' function getprev
'searches For the previous key in the index from present position in globalinf$(2)
'with Name=indexname and keylength=keylength
' returns position in masterfile of previous
Function getprev(indexname$,keylength)
Open indexname$ For Binary As #oi9
i=Val(globalinf$(2))- 1
If i < 1 Then
Notice"bof reached"
i=0:getprev=0
Else
pointer =(i-1)*(5+keylength)
Seek #oi9,pointer
key$=Input$(#oi9,5+keylength )
adress$=Mid$(key$,keylength+1):adress=Val(adress$)
key$=Left$(key$,keylength)
key$=Trim$(key$)
getprev=adress
globalinf$(1)=indexname$
globalinf$(2)=Str$(i)
globalinf$(3)=adress$
globalinf$(4)=key$
End If
Close #oi9
End Function
'-------------------------------------------------------------------------------
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