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ZBasic Language Reference
84
ZX Microcontroller Family
Structure MyTimeStamp
Public tdate as MyDate
Public ttime as MyTime
Private isCurrent as Boolean
End Structure
Sub Main()
Dim ts as MyTimeStamp
Call GetTimeStamp(ts.tdate.year, ts.tdate.month, ts.tdate.day, _
ts.ttime.hour, ts.ttime.minute, ts.ttime.seconds)
End Sub
The example above illustrates how members of an instance of a structure are referenced. The variable
ts is an instance of the MyTimeStamp structure. A member is referenced by appending the member
name to the variable name, separating them with a period. For members that are structures, members of
the subordinate structure are referred to similarly. No spaces are allowed in this construction. In cases
where a variable or a member is an array, the index list directly follows the variable/member name,
preceding the period.
Structure foo
Dim b as Byte
Dim ai(1 to 10) as Integer
Dim ts(1 to 4) as MyTimeStamp
End Structure
Dim yr as UnsignedInteger
Dim i as Integer
Dim f as foo
Dim b as Byte
i = f.ai(b)
yr = f.ts(3).tdate.year
The address of a member of a variable that is a structure may be obtained by appending the
.DataAddress property identifier to the reference or by using the MemAddress() function.
Dim addr as UnsignedInteger
addr = ts.tdate.DataAddress
addr = MemAddressU(ts.tdate)
Structures may be used in Alias and Based variable definitions. However, in these cases the structures
may not contain members that are any of the string types. Structures may be passed to subroutines and
functions either by reference or by value. If a structure is passed by value, the structure will be read-only
within the procedure.
A variable that is a structure may be assigned to another variable that is the same type of structure using
the standard assignment operator. In most cases, the compiler produces code to implement the copy
operation using a simple memory-to-memory copy operation. However, in cases where the structure
contains one or more members that are of the allocated string type (or has members that are structures
which have such members), the compiler uses a special copy procedure that ensures the correct result.
Moreover, two variables that are the same type of structure may be compared for equality or inequality
using the standard comparison operators, = and <>. The equality/inequality test is implemented using a
byte-by-byte comparison of the content of two structures. If one or more members of the structure are the
BoundedString type, the byte-by-byte comparision may result in a False value even though the strings are
identical. This is because the currently-unused portion of the string store may contain byte values that
are different between the two instances being compared. Similarly, comparison of structures containing
allocated strings, while allowed, is not recommended because of the likelihood of resulting in false
negatives.
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