ZBasic Language Reference
90
ZBasic Microcontrollers
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.
Structures may contain members that are sub-byte types, Bit and Nibble. Members that are Bit type
will be aligned on the next available bit boundary and those that are Nibble type will be aligned on the
next available nibble boundary. If a member that is not a sub-byte type follows a sub-byte type member,
that non-sub-byte member will be aligned on the next available byte boundary. Depending on how you
define your structure, this may result in “holes” in the structure layout representing unused bits. The
unused bits are generally of no consequence but it is important to note that these “holes” may interfere
with the equality/inequality test for structures that are not initialized because the unused bits will have an
indeterminate value. You can avoid this potential problem by performing a block initialization on locally
defined structures.
Example
' this structure contains a "hole", unused bits following the ab member
Structure foo
Dim b as Byte
Dim ab(1 to 4) as Bit
Dim b2 as Byte
End Structure
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