Random Access File

Tutorial 8

• Terminology
• Field – single item of information(attribute) about an object(person, place, thing)
• Record – group of related fields, that contain all the attributes of an object
• Data File – collection of related records
• Sequential access – records can only be retrieved or stored in order
• Random access file – records can be retrieved in any order
• Each record has a unique record number which is used to access the record
• All records are the same size – fixed length records
• Spaces used to pad
• No comma as separators, no quotation marks around strings
• New Statements
• TYPE
• Type {structure name}
•     Field1 as datatype
•     Field2 as datatype
• end type
• example

Type addrrec

            StrName as string * 30

            StrAddr as string *30

            StrCity as string 40

            StrState as string * 2

End type

Dim addressEntry as addrec                                             

·        Relative file

o       Open {filename} for random as #1 len= len(adddressEntry)

o       Writing to a relative file

§         Put #filenumber, {recnumber}, {record}

§         File written in binary

o       Reading from a relative file

§         Get #1, {recnumber}, {{record}

·        User Define Procedure

o       Sub {routineName} ( {{byval},byref} {}varname} as {Variable type} ,….)

o       Byref is default

§         Byref – variable actual address passed, contents of variable can be cahnged

§         Byval – copy of variable made, changes made to copy, original variable left unchanged

·        Trim – function that removes both leading and trailing spaces and returns the new string leaving original string unchanged

o       Trim({string variable})

·        Forms

o       Load {formname} – load form into memory, form not displayed

o       {formname}.show – show form, load into memory if not previously loaded

o       {formname.hide} – removes form from screen, form still in memory

o       unload {formname} – removes form from memory