Delphi in a Nutshell

Name

ReallocMem Procedure

Syntax

procedure ReallocMem(var P: Pointer; NewSize: Integer);

Description

ReallocMem changes the size of a dynamically allocated block, preserving as much of the previous contents as possible.

If P is nil, ReallocMem is just like GetMem. If NewSize is zero, it is just like FreeMem, which means P is not changed, so it contains an invalid pointer after ReallocMem returns.

When possible, ReallocMem tries to adjust the size of the current memory block, but if it cannot, it allocates an entirely new block of the desired size and copies the old data into the new block. In either case, if NewSize is bigger than the current size, the extra memory is not initialized.

ReallocMem is not a real procedure.

Tips and Tricks

• If you have a block that grows incrementally, anticipate future growth. Instead of frequently increasing the block size in small steps, increase the size by larger steps less often. Try to call ReallocMem as little as possible because ReallocMem often fails to reuse the current block. As the block size grows, the performance penalty for copying the old block to the new block also grows.

• ReallocMem in Delphi’s default memory manager is thread-safe, that is, you can call ReallocMem from multiple threads simultaneously, but only if IsMultiThread is True.

• Delphi’s memory manager assumes that the program will frequently allocate and free blocks of varying sizes. Most programs fit this pattern, but a few don’t. If your program often calls ReallocMem to incrementally ...