Operator [] (Pointer Index)
Returns a reference to memory offset from an address
Syntax
`
Declare Operator [] ( ByRef lhs As T Pointer, ByRef rhs As Integer ) ByRef As T
`
Usage
`
result = lhs [ rhs ]
or
lhs [ rhs ] = value
`
Parameters
`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.
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

Differences from QB

- New to FreeBASIC

See also

- Pointer Arithmetic
- `Operator * (Value Of)`
- `Operator [] (String Index)`
- `Operator () (Array Index)`
- `Operator + (Add)`
- `Operator - (Subtract)`
- Pointer Operators