Associative Arrays max length? 32bit/64bit

[FG via Digitalmars-d]

On 2014-05-17 12:46, sdvcn wrote:
> int main(string[] argv)
> {
> auto flog = File("results.txt", "w");
>
>      size_t[string] bary;
>
>      for(size_t i=0;i<(size_t.max -1);i++)
>      {
>          bary["Key:" ~  to!(string)(i)] = i;
>          flog.write("stop i=" ~text(i));
>          flog.seek(0);
>          flog.flush();
>      }
>      return 0;
> }
>
> results:
> start i=0
> stop i=36495998
> ---------------
> start i=0
> stop i=36495992
> ----------------
> start i=36495998
> stop i=72991099
>
> I guess not see why Overflow.


This code will always make you run out of memory. Why are you surprised?

Each key in the hash table is a string in the form "Key: 1234", so at stop (i = 36495998) the string has 13 bytes. Add to that 16 bytes for slice of that string (assuming 64-bit architecture), 8 bytes for the value, some space wasted on alignment, and don't forget the extra memory needed to store the tree for fast key look-up in the hash array.

You said that you have 16 GB of memory. At i = 36495998 that means at most 470 bytes per item.

As for capturing the problem, you can catch the Out-of-memory error but you cannot do that by catch(Exception e). OutOfMemory is not an Exception. It is an Error. Here is the updated example:


     import std.stdio, std.string, std.conv, core.exception;

     int main(string[] argv) {
         size_t[string] bary;
         size_t i = 0;
         try {
             for (; i < (size_t.max - 1); i++)
                 bary["Key:" ~  to!(string)(i)] = i;
         } catch (OutOfMemoryError e) {
             writeln(e);
         }
         writefln("Last index was: %d", i);
         return 0;
     }