REALLOCATE


Reallocates storage for an existing reserved block of memory

Syntax:
declare function Reallocate cdecl ( byval pointer as any ptr, byval count as uinteger ) as any ptr

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:
Attempts to reallocate, or resize, 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.

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).

This function is not part of the FreeBASIC runtime library, it is an alias for the C runtime library's realloc, so it's not guaranteed to be thread safe in all platforms.

NOTE: Reallocating a pointer inside an object function, when that pointer contains the parent object of the function, is undefined, and will likely result in horrible crashes.

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


Dialect Differences:
Differences from QB:
See also:
Back to Memory Functions
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