byte[] buffer = new byte[500000];
initializes buffer with 0 values. As it is a buffer, I dont want any initialization, is it possible in C# as in C?
3 Answers
I don't think it is possible... Even FormatterServices.GetUninitializedObject that doesn't run constructors:
Because the new instance of the object is initialized to zero and no constructors are run, the object might not represent a state that is regarded as valid by that object.
Note that if you want unmanaged (memory taken from the OS that isn't GC-managed), that can be allocated without zeroing it, but it wouldn't be a byte[].
4 Comments
I just found a question that points out some differences between "reserved" and "committed" memory when initializing 2D arrays in .NET. See stackoverflow.com/questions/13039379/…. Do you think this extends to regular, 1D arrays?
xanatos
@Asad Yes, just checked... But if you are thinking of using unsafe code with
fixed to access the memory before it is initialized, I don't think it works :-) I think that it is the OS that allocates the memory when requested (and cleans it), not the .NET .xanatos
@Asad I'm not sure of this... There is the possibility that GC doesn't returns blocks of memory that aren't used anymore to the OS... it probably keeps them and so the first init is OS-based, while next ones are CLR done.
A way in C# to do what malloc does in C is to use Marshal.AllocHGlobal in an unsafe context:
unsafe
{
var ptr = Marshal.AllocHGlobal(50000 * sizeof(int));
int* values = (int*)ptr;
// lists uninitialized ints
for (int i = 0; i < 50000; i++)
Console.WriteLine(values[i]);
Marshal.FreeHGlobal(ptr);
}
2 Comments
Panagiotis Kanavos
Note the warnings in the method's page: it exposes LocalAlloc which applications aren't supposed to use. It is also slower than heap allocation methods
Panagiotis Kanavos
In fact, the OP should probably use BufferManager to allocate reusable buffers from one initial block of memory rather than allocate new buffers, even if they aren't initialized
Fill it with random numbers or use DllImport and VirtualAlloc from Win32 API.
3 Comments
xanatos
From VirtualAlloc: Reserves or commits a region of memory within the virtual address space of a specified process. The function initializes the memory it allocates to zero, unless MEM_RESET is used., and for MEM_RESET: Indicates that data in the memory range specified by lpAddress and dwSize is no longer of interest. so it can't be used on first call.
i486
Ok, there is
GlobalAlloc + GlobalLock to alloc uninitialized memory. It can be used as source of "random" memory. I suspect the author want to catch values in RAM from other processes...xanatos
There is even the
HeapAlloc to do it.
bufferto benull?0is the default value forbyte, what would you actually want to happen?malloc) I don't think it is possible.