This question already has answers here:
What is the Maximum Size that an Array can hold?
(6 answers)
Closed 4 years ago.
I have some folder that might contain a lot of files, I want to know what's the maximum size that string array can hold, I mean how many file names the array:
string[] files=Directory.GetFiles(#"c:\Dir\"); can hold?
Note that I'm asking about string array, not something else please.
Array Class
By default, the maximum size of an Array is 2 gigabytes (GB). In a
64-bit environment, you can avoid the size restriction by setting the
enabled attribute of the gcAllowVeryLargeObjects configuration element
to true in the run-time environment. However, the array will still be
limited to a total of 4 billion elements, and to a maximum index of
0X7FEFFFFF in any given dimension (0X7FFFFFC7 for byte arrays and
arrays of single-byte structures).
Very useful comment by Ňuf
But is should be noted that strings themself do not count towards the
2GB size limit, because the array contains only references to these
strings. So the maximal number of elements in string array is approx.
500M in 32bit process and 2G in 64bit process. Also this limit only
applies to .NET CLR, other implementations may have different limits
(e.g. Mono on 64bit supports even larger arrays with
–enable-big-arrays option)
Related
This question already has answers here:
C# reference of 2nd dim array to 1d array
(1 answer)
What is the most efficient way of storing data between a multi-dimension array, and a single array?
(3 answers)
Closed 2 years ago.
I know that there is already a question about converting a multidimensional array into a one dimensional one, but all of the answers to it are inefficient. All of them are based around making a copy of the array, which is unnecessary. A multidimensional array (not jagged) is stored in a contiguous block of memory, so converting back and forth between a one dimensional interpretation of this block and a multidimensional interpretation should not involve copying the whole array, but instead should be essentially free. It should actually be possible to have the two arrays share the same memory, so that when one gets updated, the other one also does.
Can this be done in C#?
No, you cannot. Quite apart from anything else, arrays, like many things in .NET are objects. That means that they have an object header positioned immediately before other memory used for storing their representation.
Logically, you cannot have two different object headers, for two different types of objects, occupying the same location in memory.
Well, the data itself if pretty much stored the same way, but the wrapping around that - the managed array type - is what's stopping you from accessing it directly.
The managed array, as Damien pointed out, has different headers for one or multidimensional kinds, for example, multidimensional array's header has more fields - to store the dimension values.
The arrays themselves are maintained by IL and GC and their "data memory" part could not be "frozen" so that the headers could be swapped from one to another, if you'd want to write directly to RAM to switch them.
I'm also concerned that there is an XY problem. Why indeed are you trying to convert one array to another? Is there a reason you cannot just use this instead?
public static T Get<T>(this T[] array, int x, int y, int maxX)
{
return T[x + y * maxX];
}
Or even write your own wrapper around an array and provide both Get[index/indices] methods from there?
This question already has answers here:
What is the maximum possible length of a .NET string?
(8 answers)
Closed 4 years ago.
I know in C# you can do int.MaxValue or long.MaxValue to get the maximum for these two types, I was wondering if there are similar ways to get the maximum length for the string.
I don't see it here.
Also, I am aware that there are already questions being asked on max string length. Max string length in C#
I am asking if there is an existing function that comes in handy where you can use it to set the condition when and when not to truncate your string to avoid program crashing.
Or what is the normal approach?
E.g. Maybe something as easy as Max(string.length)?
No. In the same way that there is no known method to find the max length of an array you can allocate. Until you try to allocate the memory, you can't know if there is enough virtual address space and enough physical memory to contain it. Theorically you could VirtualAlloc (Windows API) greater and greater memory blocks until it fails, deallocate the block and then try to allocate the same amount of memory in .NET, knowing that the memory is there so the .NET should be able to allocate it.
Note that this is true at 32 bits... I haven't ever seen an out-of-memory error at 64 bits.
This question already has answers here:
What is the Maximum Size that an Array can hold?
(6 answers)
Closed 4 years ago.
byte[] buffer2 = new byte[4294743227]; // string with System.OverflowException
The number 4294743227 is uint.
Why do i get exception?
According to this question, the maximum size of an array is System.Int32.MaxValue, which is 2,147,483,647.
See also the documentation on System.Array:
By default, the maximum size of an Array is 2 gigabytes (GB). In a
64-bit environment, you can avoid the size restriction by setting the
enabled attribute of the gcAllowVeryLargeObjects configuration element
to true in the run-time environment. However, the array will still be
limited to a total of 4 billion elements, and to a maximum index of
0X7FEFFFFF in any given dimension (0X7FFFFFC7 for byte arrays and
arrays of single-byte structures).
This question already has an answer here:
How to allocate arrays on the stack for performance gains?
(1 answer)
Closed 7 years ago.
I am writing a program in C#. Everything centers around a static 2D int array which is 400x6 elements. Just a few values will be updated just once every minute. But after each minute's updates, dozens of functions will read the values millions of times to compute "pattern scores". The faster the calculations, the more distinct functions I can cram in there. Realistically I can allow 30 seconds for this scoring process. Is there a way to allocate the static array to the stack, and if so, would this help the speed? Thanks.
Yes, you can alloc arrays on the stack in C# using "stackalloc" in "unsafe mode", but benchmarks shows a limited performance gain and the risk is that you hit the 1Mb stack size limit... which will give you a... StackOverflow(tm)!
Here is a good article on the subject:
http://blogs.microsoft.co.il/sasha/2013/10/17/on-stackalloc-performance-and-the-large-object-heap/
You can use "stackalloc" to alloc array directly on the stack.
Some documentation about :
https://msdn.microsoft.com/en-us/library/aa664785(v=vs.71).aspx
You can also use an implementation of Hamming weight which is describe here :
How to allocate arrays on the stack for performance gains?
This question already has answers here:
How do you deal with numbers larger than UInt64 (C#)
(8 answers)
Closed 8 years ago.
Hi all I am having a numeric digit with 20 characters as follows 34432523434234423434, I tried this converting using long,UInt64 but still I am getting an exception Value was either too large or too small so can some one help me out how can I convert this value
Your value is actually 65 bits long, so doesn't matter HOW you change its type, it will not fit into a 64bit variable.
2**64 = 18446744073709551616
your value = 34432523434234423434
Big integers aren't actually limited to 20 digits, they're limited to the numbers that can be expressed in 64 bits (for example, the number 99,999,999,999,999,999,999 is not a valid big integer despite it being 20 digits long).
The reason you have this limitation is that native format integers can be manipulated relatively fast by the underlying hardware whereas textual versions of a number (tend to) need to be processed one digit at a time.
If you want a number larger than the largest 64-bit unsigned integer 18,446,744,073,709,551,615 then you will need to store it as a string (or other textual field) and hope that you don't need to do much mathematical manipulation on it.
Alternatively, you can look into floating point numbers which have a larger range but less precision, or decimal numbers which should be able to give you 65 digits for an integral value, with decimal(65,0) as the column type.