REALLOCATE
Reallocates storage for an existing reserved block of memory
Syntax:
Usage:
result = Reallocate( pointer, count )
Parameters:
pointer
The address of allocated memory to be reallocated.
count
The number of bytes, in total, to be reallocated.
Return Value:
The address of the reallocated memory. A null (0) pointer is returned if reallocation was unsuccessful, and the original memory pointed to by pointer remains unchanged.
Description:
Reallocates memory previously allocated with Allocate or Callocate. The contents of the buffer are preserved, although if count is less than the original size of the memory block, the buffer will be truncated. If the size is increased, the added memory range is not initialized to anything.
The reallocation first attempts to resize the memory already allocated without moving its starting address in order to avoid recopying the data to be kept (returned pointer value unchanged). If this is not possible, a new separate memory area is allocated with recopy of the data to be kept before deallocating the old memory area (returned pointer value modified).
When using Reallocate, the result pointer must be saved to prevent a potential memory leak, because the original pointer may no longer be valid after reallocation. The value of the new pointer should be checked - if it is 0, the reallocation has failed - the original pointer remains valid, and the amount of memory allocated to it has not changed.
Reallocated memory must be freed with Deallocate when no longer needed.
If pointer is null (0), then ReAllocate behaves identically to Allocate. If pointer is valid and count is null (0), then ReAllocate behaves similar to Deallocate and a null (0) pointer is returned.
If the memory has previously been deallocated by a call to Deallocate or ReAllocate, the behavior is undefined.
When manually allocating memory for String descriptors (or UDTs that contain one), if count is larger than the original size of the memory block, the new extra memory range must be explicitly cleared to zeroes before the first string use (for example, using Clear). Otherwise accessing the string will cause undefined results (trying to write or read at a random place in memory, or trying to deallocate a random pointer).
Note:
The reallocation first attempts to resize the memory already allocated without moving its starting address in order to avoid recopying the data to be kept (returned pointer value unchanged). If this is not possible, a new separate memory area is allocated with recopy of the data to be kept before deallocating the old memory area (returned pointer value modified).
When using Reallocate, the result pointer must be saved to prevent a potential memory leak, because the original pointer may no longer be valid after reallocation. The value of the new pointer should be checked - if it is 0, the reallocation has failed - the original pointer remains valid, and the amount of memory allocated to it has not changed.
Reallocated memory must be freed with Deallocate when no longer needed.
If pointer is null (0), then ReAllocate behaves identically to Allocate. If pointer is valid and count is null (0), then ReAllocate behaves similar to Deallocate and a null (0) pointer is returned.
If the memory has previously been deallocated by a call to Deallocate or ReAllocate, the behavior is undefined.
When manually allocating memory for String descriptors (or UDTs that contain one), if count is larger than the original size of the memory block, the new extra memory range must be explicitly cleared to zeroes before the first string use (for example, using Clear). Otherwise accessing the string will cause undefined results (trying to write or read at a random place in memory, or trying to deallocate a random pointer).
Note:
Reallocate cannot be used inside a member procedure if pointer points to the instance itself of the object, because that could cause horrible crashes:
- If pointer is modified by Reallocate (object data moved into memory), the passed This reference becomes inconsistent, in the same way as a dangling pointer.
- In that case, all subsequent accesses to any non-static member field from this member procedure will be erroneous, except if the passed This reference would be readjusted (by means of @This = new pointer value) immediately after executing Reallocate in the body of this member procedure.
Examples:
Dim a As Integer Ptr, b As Integer Ptr, i As Integer
a = Allocate( 5 * SizeOf(Integer) ) ' Allocate memory for 5 integers
If a = 0 Then Print "Error Allocating a": End
For i = 0 To 4
a[i] = (i + 1) * 2 ' Assign integers to the buffer
Next i
b = Reallocate( a, 10 * SizeOf(Integer) ) ' Reallocate memory for 5 additional integers
If b <> 0 Then
a = b ' Discard the old pointer and use the new one
For i = 5 To 9
a[i] = (i + 1) * 2 ' Assign more integers to the buffer
Next i
For i = 0 To 9 ' Print the integers
Print i, a[i]
Next i
Print
Else '' Reallocate failed, memory unchanged
Print "Error Reallocating a"
For i = 0 To 4 ' Print the integers
Print i, a[i]
Next i
Print
End If
Deallocate a ' Clean up
a = Allocate( 5 * SizeOf(Integer) ) ' Allocate memory for 5 integers
If a = 0 Then Print "Error Allocating a": End
For i = 0 To 4
a[i] = (i + 1) * 2 ' Assign integers to the buffer
Next i
b = Reallocate( a, 10 * SizeOf(Integer) ) ' Reallocate memory for 5 additional integers
If b <> 0 Then
a = b ' Discard the old pointer and use the new one
For i = 5 To 9
a[i] = (i + 1) * 2 ' Assign more integers to the buffer
Next i
For i = 0 To 9 ' Print the integers
Print i, a[i]
Next i
Else '' Reallocate failed, memory unchanged
Print "Error Reallocating a"
For i = 0 To 4 ' Print the integers
Print i, a[i]
Next i
End If
Deallocate a ' Clean up
- Not available in the -lang qb dialect unless referenced with the alias __Reallocate.
Differences from QB:
- New to FreeBASIC
See also:
Back to Memory Functions
