Operator [] (Pointer Index)operator

Returns a reference to memory offset from an address

Operatorsoperatordocumented

Syntax

Declare Operator [] ( ByRef lhs As T Pointer, ByRef rhs As Integer ) ByRef As T

Parameters

Name		Description
`lhs`		The base address.
`rhs`		A signed offset from
`lhs`		.
`T`		Any data type.

Description

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 exactly the same thing.
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 second: For example, Pt[I1][I2] = *(Pt[I1] + I2) = *(*(Pt + I1) + I2)
In general, when using an 'n-dimensional' pointer: Pt[I1][I2].....[In], the index order (from left 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 operator can be overloaded for user-defined types as a member Operator using the appropriate syntax.

Remarks

Usage



result = lhs [ rhs ]

or

lhs [ rhs ] = value

Differences from QB

New to FreeBASIC

Example

'' initialize a 5-element array

Dim array(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];

Next

Print

Will give the output,

 0 1 2 3 4

Reference

Documented in KeyPgOpPtrIndex.html