struct Pointer(T)
Overview
A typed pointer to some memory.
This is the only unsafe type in Crystal. If you are using a pointer, you are writing
unsafe code because a pointer doesn't know where it's pointing to nor how much memory
starting from it is valid. However, pointers make it possible to interface with C and
to implement efficient data structures. For example, both Array
and Hash
are
implemented using pointers.
You can obtain pointers in four ways: #new
, #malloc
, pointerof
and by calling a C
function that returns a pointer.
pointerof(x)
, where x
is a variable or an instance variable, returns a pointer to
that variable:
x = 1
ptr = pointerof(x)
ptr.value = 2
puts x # => 2
Note that a pointer is falsey if it's null (if it's address is zero).
When calling a C function that expects a pointer you can also pass nil
instead of using
Pointer.null
to construct a null pointer.
For a safe alternative, see Slice
, which is a pointer with a size and with bounds checking.
Included Modules
- Comparable(Pointer(T))
Defined in:
pointer.crprimitives.cr
Class Method Summary
-
.malloc(size : UInt64)
Allocates
size * sizeof(T)
bytes from the system's heap initialized to zero and returns a pointer to the first byte from that memory. -
.malloc(size : Int = 1)
Allocates
size * sizeof(T)
bytes from the system's heap initialized to zero and returns a pointer to the first byte from that memory. -
.malloc(size : Int, &block : Int32 -> T)
Allocates
size * sizeof(T)
bytes from the system's heap initialized to the value returned by the block (which is invoked once with each index in the range0...size
) and returns a pointer to the first byte from that memory. -
.malloc(size : Int, value : T)
Allocates
size * sizeof(T)
bytes from the system's heap initialized to value and returns a pointer to the first byte from that memory. -
.new(address : UInt64)
Returns a pointer that points to the given memory address.
-
.new(address : Int)
Returns a pointer that points to the given memory address.
-
.null
Returns a pointer whose memory address is zero.
Instance Method Summary
-
#+(other : Int)
Returns a new pointer whose address is this pointer's address incremented by
other * sizeof(T)
. -
#+(offset : Int64) : self
Returns a new pointer whose address is this pointer's address incremented by
other * sizeof(T)
. -
#-(other : self) : Int64
Returns how many T elements are there between this pointer and other.
-
#-(other : Int)
Returns a new pointer whose address is this pointer's address decremented by
other * sizeof(T)
. -
#<=>(other : self)
Returns -1, 0 or 1 if this pointer's address is less, equal or greater than other's address, respectively.
-
#[](offset)
Gets the value pointed at this pointer's address plus
offset * sizeof(T)
. -
#[]=(offset, value : T)
Sets the value pointed at this pointer's address plus
offset * sizeof(T)
. -
#address : UInt64
Returns the address of this pointer.
-
#appender
Returns a
Pointer::Appender
for this pointer. -
#clear(count = 1)
Clears (sets to "zero" bytes) a number of values pointed by this pointer.
- #clone
-
#copy_from(source : Pointer(T), count : Int)
Copies count elements from source into self.
-
#copy_to(target : Pointer, count : Int)
Copies count elements from self into target.
-
#hash
Returns the address of this pointer.
-
#map!(count : Int, &block)
Sets count consecutive values pointed by this pointer to the values returned by the block.
-
#memcmp(other : Pointer(T), count : Int)
Compares count elements from this pointer and other, byte by byte.
-
#move_from(source : Pointer(T), count : Int)
Copies count elements from source into self.
-
#move_to(target : Pointer, count : Int)
Copies count elements from self into source.
-
#null?
Returns true if this pointer's address is zero.
-
#realloc(size : UInt64) : self
Tries to change the size of the allocation pointed to by this pointer to size, and returns that pointer.
-
#realloc(size : Int)
Tries to change the size of the allocation pointed to by this pointer to size, and returns that pointer.
-
#shuffle!(count : Int, random = Random::DEFAULT)
Shuffles count consecutive values pointed by this pointer.
-
#swap(i, j)
Swaps the contents pointed at the offsets
i
andj
. -
#to_s(io : IO)
Appends a string representation of this pointer to the given
IO
, including its type and address in hexadecimal. -
#to_slice(size)
Returns a
Slice
that points to this pointer and is bounded by the given size. -
#value : T
Gets the value pointed by this pointer.
-
#value=(value : T)
Sets the value pointed by this pointer.
Instance methods inherited from module Comparable({"T", T})
<(other : T)
<,
<=(other : T)
<=,
<=>(other : T)
<=>,
==(other : T)
==,
>(other : T)
>,
>=(other : T)
>=
Instance methods inherited from struct Value
==(other)
==,
dup
dup
Instance methods inherited from class Object
!=(other)
!=,
!~(other)
!~,
==(other)
==,
===(other)===(other : YAML::Any)
===(other : JSON::Any) ===, =~(other) =~, class class, crystal_type_id crystal_type_id, dup dup, hash hash, inspect(io : IO)
inspect inspect, itself itself, not_nil! not_nil!, tap(&block) tap, to_json to_json, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ") to_pretty_json, to_s
to_s(io : IO) to_s, to_yaml
to_yaml(io : IO) to_yaml, try(&block) try
Class methods inherited from class Object
==(other : Class)
==,
===(other)
===,
cast(other) : self
cast,
clone
clone,
dup
dup,
from_json(string_or_io) : selffrom_json(string_or_io, root : String) : self from_json, from_yaml(string : String) : self from_yaml, hash hash, inspect(io) inspect, name : String name, nilable? nilable?, to_s(io) to_s, |(other : U.class) forall U |
Class Method Detail
Allocates size * sizeof(T)
bytes from the system's heap initialized
to zero and returns a pointer to the first byte from that memory.
The memory is allocated by the GC
, so when there are
no pointers to this memory, it will be automatically freed.
# Allocate memory for an Int32: 4 bytes
ptr = Pointer(Int32).malloc(1_u64)
ptr.value #=> 0
# Allocate memory for 10 Int32: 40 bytes
ptr = Pointer(Int32).malloc(10_u64)
ptr[0] #=> 0
...
ptr[9] #=> 0
Allocates size * sizeof(T)
bytes from the system's heap initialized
to zero and returns a pointer to the first byte from that memory.
The memory is allocated by the GC
, so when there are
no pointers to this memory, it will be automatically freed.
# Allocate memory for an Int32: 4 bytes
ptr = Pointer(Int32).malloc
ptr.value #=> 0
# Allocate memory for 10 Int32: 40 bytes
ptr = Pointer(Int32).malloc(10)
ptr[0] #=> 0
...
ptr[9] #=> 0
Allocates size * sizeof(T)
bytes from the system's heap initialized
to the value returned by the block (which is invoked once with each index in the range 0...size
)
and returns a pointer to the first byte from that memory.
The memory is allocated by the GC
, so when there are
no pointers to this memory, it will be automatically freed.
# An Int32 occupies 4 bytes, so here we are requesting 16 bytes.
# i is an index in the range 0 .. 3
ptr = Pointer.malloc(4) { |i| i + 10 }
ptr[0] # => 10
ptr[1] # => 11
ptr[2] # => 12
ptr[3] # => 13
Allocates size * sizeof(T)
bytes from the system's heap initialized
to value and returns a pointer to the first byte from that memory.
The memory is allocated by the GC
, so when there are
no pointers to this memory, it will be automatically freed.
# An Int32 occupies 4 bytes, so here we are requesting 8 bytes
# initialized to the number 42
ptr = Pointer.malloc(2, 42)
ptr[0] # => 42
ptr[1] # => 42
Returns a pointer that points to the given memory address. This doesn't allocate memory.
ptr = Pointer(Int32).new(5678_u64)
ptr.address # => 5678
Returns a pointer that points to the given memory address. This doesn't allocate memory.
ptr = Pointer(Int32).new(5678)
ptr.address # => 5678
Returns a pointer whose memory address is zero. This doesn't allocate memory.
When calling a C function you can also pass nil
instead of constructing a
null pointer with this method.
ptr = Pointer(Int32).null
ptr.address # => 0
Instance Method Detail
Returns a new pointer whose address is this pointer's address incremented by other * sizeof(T)
.
ptr = Pointer(Int32).new(1234)
ptr.address # => 1234
# An Int32 occupies four bytes
ptr2 = ptr + 1
ptr2.address # => 1238
Returns a new pointer whose address is this pointer's address incremented by other * sizeof(T)
.
ptr = Pointer(Int32).new(1234)
ptr.address # => 1234
# An Int32 occupies four bytes
ptr2 = ptr + 1_u64
ptr2.address # => 1238
Returns how many T elements are there between this pointer and other.
That is, this is (self.address - other.address) / sizeof(T)
.
ptr1 = Pointer(Int32).malloc(4)
ptr2 = ptr1 + 2
ptr2 - ptr1 # => 2
Returns a new pointer whose address is this pointer's address decremented by other * sizeof(T)
.
ptr = Pointer(Int32).new(1234)
ptr.address # => 1234
# An Int32 occupies four bytes
ptr2 = ptr - 1
ptr2.address # => 1230
Returns -1, 0 or 1 if this pointer's address is less, equal or greater than other's address, respectively.
See Object#<=>
.
Gets the value pointed at this pointer's address plus offset * sizeof(T)
.
ptr = Pointer.malloc(4) { |i| i + 10 }
ptr[0] # => 10
ptr[1] # => 11
ptr[2] # => 12
ptr[3] # => 13
Sets the value pointed at this pointer's address plus offset * sizeof(T)
.
ptr = Pointer(Int32).malloc(4) # [0, 0, 0, 0]
ptr[1] = 42
ptr2 = ptr + 1
ptr2.value # => 42
Returns the address of this pointer.
ptr = Pointer(Int32).new(1234)
ptr.address # => 1234
Clears (sets to "zero" bytes) a number of values pointed by this pointer.
ptr = Pointer.malloc(6) { |i| i + 10 } # [10, 11, 12, 13, 14, 15]
ptr.clear(3)
ptr # [0, 0, 0, 13, 14, 15]
Copies count elements from source into self.
If source and self overlap, behaviour is undefined.
Use #move_from
if they overlap (slower but always works).
ptr1 = Pointer.malloc(4) { |i| i + 1 } # [1, 2, 3, 4]
ptr2 = Pointer.malloc(4) { |i| i + 11 } # [11, 12, 13, 14]
# ptr2 -> [11, 12, 13, 14]
# ^---^ <- copy this
# ptr1 -> [1, 2, 3, 4]
# ^---^ <- here
ptr1.copy_from(ptr2, 2)
ptr1[0] # => 11
ptr1[1] # => 12
ptr1[2] # => 3
ptr1[3] # => 4
Copies count elements from self into target.
If self and target overlap, behaviour is undefined.
Use #move_to
if they overlap (slower but always works).
ptr1 = Pointer.malloc(4) { |i| i + 1 } # [1, 2, 3, 4]
ptr2 = Pointer.malloc(4) { |i| i + 11 } # [11, 12, 13, 14]
# ptr1 -> [1, 2, 3, 4]
# ^---^ <- copy this
# ptr2 -> [11, 12, 13, 14]
# ^---^ <- here
ptr1.copy_to(ptr2, 2)
ptr2[0] # => 1
ptr2[1] # => 2
ptr2[2] # => 13
ptr2[3] # => 14
Sets count consecutive values pointed by this pointer to the values returned by the block.
ptr = Pointer.malloc(4) { |i| i + 1 } # [1, 2, 3, 4]
ptr.map!(4) { |value| value * 2 }
ptr # [2, 4, 6, 8]
Compares count elements from this pointer and other, byte by byte.
Returns 0 if both pointers point to the same sequence of count bytes. Otherwise returns the difference between the first two differing bytes (treated as UInt8).
ptr1 = Pointer.malloc(4) { |i| i + 1 } # [1, 2, 3, 4]
ptr2 = Pointer.malloc(4) { |i| i + 11 } # [11, 12, 13, 14]
ptr1.memcmp(ptr2, 4) # => -10
ptr2.memcmp(ptr1, 4) # => 10
ptr1.memcmp(ptr1, 4) # => 0
Copies count elements from source into self. source and self may overlap; the copy is always done in a non-destructive manner.
ptr1 = Pointer.malloc(4) { |i| i + 1 } # ptr1 -> [1, 2, 3, 4]
ptr2 = ptr1 + 1 # ^--------- ptr2
# [1, 2, 3, 4]
# ^-----^ <- copy this
# ^------^ <- here
ptr2.move_from(ptr1, 3)
ptr1[0] # => 1
ptr1[1] # => 1
ptr1[2] # => 2
ptr1[3] # => 3
Copies count elements from self into source. source and self may overlap; the copy is always done in a non-destructive manner.
ptr1 = Pointer.malloc(4) { |i| i + 1 } # ptr1 -> [1, 2, 3, 4]
ptr2 = ptr1 + 1 # ^--------- ptr2
# [1, 2, 3, 4]
# ^-----^ <- copy this
# ^------^ <- here
ptr1.move_to(ptr2, 3)
ptr1[0] # => 1
ptr1[1] # => 1
ptr1[2] # => 2
ptr1[3] # => 3
Returns true if this pointer's address is zero.
a = 1
pointerof(a).null? # => false
b = Pointer(Int32).new(0)
b.null? # => true
Tries to change the size of the allocation pointed to by this pointer to size, and returns that pointer.
Since the space after the end of the block may be in use, realloc may find it necessary to copy the block to a new address where more free space is available. The value of realloc is the new address of the block. If the block needs to be moved, realloc copies the old contents.
Remember to always assign the value of realloc.
ptr = Pointer.malloc(4) { |i| i + 1 } # [1, 2, 3, 4]
ptr = ptr.realloc(8_u8)
ptr # [1, 2, 3, 4, 0, 0, 0, 0]
Tries to change the size of the allocation pointed to by this pointer to size, and returns that pointer.
Since the space after the end of the block may be in use, realloc may find it necessary to copy the block to a new address where more free space is available. The value of realloc is the new address of the block. If the block needs to be moved, realloc copies the old contents.
Remember to always assign the value of realloc.
ptr = Pointer.malloc(4) { |i| i + 1 } # [1, 2, 3, 4]
ptr = ptr.realloc(8)
ptr # [1, 2, 3, 4, 0, 0, 0, 0]
Shuffles count consecutive values pointed by this pointer.
ptr = Pointer.malloc(4) { |i| i + 1 } # [1, 2, 3, 4]
ptr.shuffle!(4)
ptr # [3, 4, 1, 2]
Swaps the contents pointed at the offsets i
and j
.
ptr = Pointer.malloc(4) { |i| i + 1 }
ptr[2] # => 3
ptr[3] # => 4
ptr.swap(2, 3)
ptr[2] # => 4
ptr[3] # => 3
Appends a string representation of this pointer to the given IO
,
including its type and address in hexadecimal.
ptr1 = Pointer(Int32).new(1234)
ptr1.to_s # => Pointer(Int32)@0x4D2
ptr2 = Pointer(Int32).new(0)
ptr2.to_s # => Pointer(Int32).null
Returns a Slice
that points to this pointer and is bounded by the given size.
ptr = Pointer.malloc(6) { |i| i + 10 } # [10, 11, 12, 13, 14, 15]
slice = ptr.to_slice(4) # => [10, 11, 12, 13]
slice.class # => Slice(Int32)
Gets the value pointed by this pointer.
ptr = Pointer(Int32).malloc(4)
ptr.value = 42
ptr.value # => 42
Sets the value pointed by this pointer.
ptr = Pointer(Int32).malloc(4)
ptr.value = 42
ptr.value # => 42