Custom Database Applications
Despite having no built-in, standard database support, several of the file and string functions can be used to create simple, fast database applications where the database consists of records/lines of string data.
For example, suppose a database record includes a name, state and zip code and that a file "data.txt" contains the following three records.
Bob:::Texas:::75300 Mary:::Arkansas:::77001 Helen:::Maine:::45622
Note that any separating character string can be used as long as it will not be used as data in any of the records. In this example, ":::" was used because because no Name/State/Zip will never be that value.
A simple database application using this basic file structure would be as follows. The basic technique is to put each text line into a string array, then use PowerBASIC functions to pull out fields from each record as needed. When all changes are made to the array, simply write it back out to the file, overwriting any prior content.
1. Open Database (read text lines into array): Open "data.txt" For Input as #1 Dim MyData() as String 'first way to create array with 1 record per element 'resizes array each time it reads a line of text While NOT eof(1) Line Input #1, MyData(Ubound) if NOT eof(1) then REDIM Preserve MyData(Ubound(MyData)+1) end if Wend 'second way to crate array with 1 record per element 'uses filescan to count number of lines FILESCAN #1, RECORDS to iCount REDIM MyDATA(iCount-1) For i = 0 to UBound(MyData) Line Input #1, MyData(i) Next i 'third way to create array with 1 record per element 'if all records contain same number of characters iCount = LOF(1) / iRecordSize REDIM MyDATA(iCount-1) For i = 0 to UBound(MyData) Line Input #1, MyData(i) Next i Close #1 2. Get/Set Name/State/Zip from any array element Dim RecordData(2) As String '3 elements Dim iRecord as Long For i = 0 to Ubound(MyArray) 'first way to get Name/State/Zip PARSE MyData(iRecord), RecordData 'separates data Name$ = MyData(0) 'optional, for convenience only State$ = MyData(1) 'optional, for convenience only Zip$ = MyData(2) 'optional, for convenience only 'second way to get Name/State/Zip Name$ = Parse$(MyData(iRecord), ":::", 1) State$ = Parse$(MyData(iRecord), ":::", 2) Zip$ = Parse$(MyData(iRecord), ":::", 3) 'now use Name/State/Zip (including setting their values) .... program statements using values .... assign values to Name$, State$, Zip$ 'save results MyData(iRecord) = Build$(Name$, ":::", State$, ":::", Zip$) Next i 2A. 'Use ARRAY INSERT to add records 'Use ARRAY DELETE to delete records 'Use ARRAY SCAN to search 'Use ARRAY SORT to sort records 3. Write changed array to file: Open "data.txt" for Output as #1 For i = 0 to Ubound(MyArray) Print #1, MyArray(i) Next i
For syntax and examples, follow the links to FILESCAN, PARSE and REDIM. These functions were used in the above approaches to treating a text file as a database.
If you have any suggestions or corrections, please let me know.