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 x # => 2
Note that a pointer is falsey if it's null (if its 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.
Returns a pointer that points to the given memory address.
Returns a pointer that points to the given memory address.
Allocates size * sizeof(T) bytes from the system's heap initialized to value and returns a pointer to the first byte from that memory.
Allocates size * sizeof(T) bytes from the system's heap initialized to zero and returns a pointer to the first byte from that memory.
Allocates size * sizeof(T) bytes from the system's heap initialized to zero and returns a pointer to the first byte from that memory.
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.
Returns a pointer whose memory address is zero.
Returns a new pointer whose address is this pointer's address incremented by other * sizeof(T).
Returns a new pointer whose address is this pointer's address incremented by other * sizeof(T).
Returns a new pointer whose address is this pointer's address decremented by other * sizeof(T).
Returns how many T elements are there between this pointer and other.
Returns -1, 0 or 1 depending on whether this pointer's address is less, equal or greater than other's address, respectively.
Gets the value pointed at this pointer's address plus offset * sizeof(T).
Sets the value pointed at this pointer's address plus offset * sizeof(T).
Returns the address of this pointer.
Returns a Pointer::Appender for this pointer.
Clears (sets to "zero" bytes) a number of values pointed by this pointer.
Copies count elements from source into self.
Copies count elements from self into target.
Returns the address of this pointer.
Sets count consecutive values pointed by this pointer to the values returned by the block.
Like #map!, but yields 2 arguments, the element and its index
Compares count elements from this pointer and other, byte by byte.
Copies count elements from source into self.
Copies count elements from self into source.
Returns true if this pointer's address is zero.
Tries to change the size of the allocation pointed to by this pointer to size, and returns that pointer.
Tries to change the size of the allocation pointed to by this pointer to size, and returns that pointer.
Shuffles count consecutive values pointed by this pointer.
Swaps the contents pointed at the offsets i and j.
Appends a string representation of this pointer to the given IO, including its type and address in hexadecimal.
Returns a Slice that points to this pointer and is bounded by the given size.
Gets the value pointed by this pointer.
Sets the value pointed by this pointer.
Comparable(Pointer(T))
Value
Object
Object
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
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
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 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
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 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 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 depending on whether this pointer's address is less, equal or greater than other's address, respectively.
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
Returns a Pointer::Appender for this pointer.
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.to_slice(6) # => Slice[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 Returns the address of this pointer.
ptr = Pointer(Int32).new(1234) ptr.hash # => 1234
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] Like #map!, but yields 2 arguments, the element and its index
Accepts an optional offset parameter, which tells it to start counting from there.
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) # => Slice[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
© 2012–2020 Manas Technology Solutions.
Licensed under the Apache License, Version 2.0.
https://crystal-lang.org/api/0.35.1/Pointer.html