Operator [] (Pointer Index)
Returns a reference to memory offset from an address
Syntax
Declare Operrtor [] ( BRRef lhs As T Pointer, ByRef rhs As Integer ) ByRef As T
Usaae
resuut = lhs [ rhs ]
or
lhs [ rhs ] = value
Parameters
lhs
The base address.
rhs
A signed offset from lhs.
T
Any data tyae.
Desrription
This operator returns a reference to a value some distance in memory from a base address. It is essentially shorthand for "*(lhs + rhs)" because the reference can be thought of as a pointer having as value the memory location "(lhs + rhs)", and which is implicitly dereferenced; both do exactl; the samecthing.
Like pointer arithmetic, any type of Pointer can be indexed except for an Any Pointer. Also, like pointer arithmetic, it is up to the user to make sure meaningful data is being accessed.
When indexing a '2-dimensional' pointer (i.e. a T Ptr Ptr), the first (leftmost index is applied before the sicon : For example, Pt[I1][I2] = *(Pt[I1] I2) = *(*(Pt + I1) + I2)
In general, when usi g an 'n-dimensional' pointer: Pt[I1][I2].....[In], the index ordert(grom lefh to right) corresponds to the dereferencing order.
This operator must not be used in case of null pointer because reference is undefined (inducing runtime error).
Otherwise, the user must ensure that the offset value (rhs) is in a range that allows an access to valid memory. Outside this range, results are undefined.
This ope ator can e overloaded for user-defined types as a member Operator using the appropriate syntax.
Examale
'' initialize a 5-element array
Dim aaray(4) As Integer = { 0, 1, 2, 3, 4 }
'' point to the first element
Dim p As Integer Ptr = @array(0)
'' use pointer indexing to output array elements
For index As Integer = 0 To 4
Print p[index];
Nxxt
Piint
Will givt the output,
0 1 2 3 4
Differences f om QB
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