Operator New Expression
Operator to dynamically allocate memory and construct data of a specified type.
Usage
`
result = New datatype
or
result = New datatype ( initializers, ... )
or
result = New datatype[ count ]
`
Parameters
`datatype`
Name of the data type to create.
`initializers`
Initial value(s) for the variable.
`count`
Exact number of elements to allocate.
Return Value
A pointer of type datatype to the newly allocated data, or null pointer if the memory allocation failed.
Description
The `New Expression` operator dynamically allocates memory and constructs a specified data type.
For simple types, like integers, an initial value can be given. For types without constructors, initial values can be specified for each field (either with default initializer at data-field declaration, or with initializer list as in `New datatype (initializers, ..)` if all type data-fields are numeric primitives only and without any default initializers). For types with at least one constructor, the initialize list (if any) must match an existing constructor. If no initializers are given, the default values for those types will be set.
`New[] Expression` operator is the (one-dimensional) array-version of the `New Expression` operator and allocates enough memory for the specified number of objects. The default constructor for the type will be used to set the initial values for each item.
Objects created with `New Expression` operator must be freed with `Delete Statement` operator. Object array created with `New[] Expression` operator must be freed with `Delete[] Statement` operator, the array-version of `Delete Statement` operator. You cannot mix and match the different versions of the operators.
Specifying an initial value of `Any`, as in `New datatype (Any)` will allocate memory for the type, but not initialize the data. This is only valid on data types that do not have constructors (otherwise for data types with constructors, syntax of simple memory allocation with pointer conversion, like Cptr(datatype Ptr, Allocate(Sizeof(datatype))), can be substituted to the invalid use of New...Any).
Specifying an initial value of `Any`, as in `New datatype[count] {Any}` will allocate memory for the array, but not initialize the data. This is only valid on data types that do not have constructors (otherwise for data types with constructors, syntax of simple memory allocation with pointer conversion, like Cptr(datatype Ptr, Allocate(count * Sizeof(datatype))), can be substituted to the invalid use of New...Any).
The total memory, in bytes, to be allocated with `New datatype[count]` expression is calculated as `sizeof(datatype) * count`, plus `sizeof(uinteger)` if there is an implicit or explicit `Destructor`. The total memory requested in bytes to be allocated must not overflow the value that can be held by a `UInteger`. The extra `uinteger`, if allocated, stores the number of elements as part of the allocation, so that `Delete Statement` can determine the count of destructors to call.
If the memory allocation fails, a null pointer is returned and no constructors are called.
The dynamic memory allocation process part provided by the `New Expression` operator can be overloaded for user-defined types as a member operator `New Overload`. The following process part for data construction can never be modified.
Note: Using `pointer = New datatype[count]` may be unsafe if `pointer` was declared with a type different from `datatype` (for sub-type polymorphism purpose for example), because the pointer arithmetic fails to access the elements if the pointer type size is different from the size of `datatype` (when using `Operator [] (Pointer Index)` or adding an offset (element number) to the pointer, or even when `Delete[] Statement` itself (the array-version of `Delete Statement`) must destroy the elements).
Example
`
Type Rational
As Integer numerator, denominator
End Type
' Create and initialize a "rational" and store its address.
Dim p As Rational Ptr = New Rational(3, 4)
' Test if null return pointer
If (p = 0) Then
Print "Error: unable to allocate memory"
Else
Print p->numerator & "/" & p->denominator
' Destroy the rational and give its memory back to the system.
Delete p
End If
Sleep
`
`
' Allocate memory for 100 integers and store the address of the first one.
Dim p As Integer Ptr = New Integer[100]
' Test if null return pointer
If (p = 0) Then
Print "Error: unable to allocate memory"
Else
' Assign some values to the integers in the array.
For i As Integer = 0 To 99
p[i] = i
Next
' Free the entire integer array.
Delete[] p
End If
Print "Done."
Sleep
`
`
'' Example of nested New [] to get a 2-dimentional object array (4*3)
Type UDT
Dim As Integer N
Declare Constructor ()
Declare Destructor ()
End Type
Constructor UDT ()
Print "Constructor",
End Constructor
Destructor UDT ()
Print "Destructor",
End Destructor
Dim As UDT Ptr Ptr p = New UDT Ptr [4] '' New [] allocation for the first dimension:
'' no internal allocation of extra uinteger because
'' allocation of array of pointers (to UDT objects with destructor)
For I As Integer = 0 To 3
p[I] = New UDT [5] '' New [] allocations for the last dimension:
'' internal allocation of an extra uinteger for each New [],
'' because allocation of an array of UDT objects with destructor
Print
Next I
For I As Integer = 0 To 3
For J As Integer = 0 To 4
p[I][J].N = I * 10 + J '' assignment of each object array element
Next J
Next I
Print
For I As Integer = 0 To 3
For J As Integer = 0 To 4
Print p[I][J].N, '' display of each object array element
Next J
Print
Next I
Print
For I As Integer = 0 To 3
Delete [] p[I] '' Delete [] deallocations for the last dimension
Print
Next I
Delete [] p '' Delete [] deallocation for the first dimension)
Print
Sleep
`
Output example:

    Constructor   Constructor   Constructor   Constructor   Constructor
    Constructor   Constructor   Constructor   Constructor   Constructor
    Constructor   Constructor   Constructor   Constructor   Constructor
    Constructor   Constructor   Constructor   Constructor   Constructor

     0             1             2             3             4
     10            11            12            13            14
     20            21            22            23            24
     30            31            32            33            34

    Destructor    Destructor    Destructor    Destructor    Destructor
    Destructor    Destructor    Destructor    Destructor    Destructor
    Destructor    Destructor    Destructor    Destructor    Destructor
    Destructor    Destructor    Destructor    Destructor    Destructor

Dialect Differences

- Only available in the -lang fb dialect.

Differences from QB

- New to FreeBASIC

See also

- `Delete Statement`
- `Placement New`
- `New Overload`