Array offset through end

Question

In C++ I could use pointer arithmetic to grab everything from a start position to the end of an array. What do you do in C# to accomplish the same thing?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static string GetText(byte[] value, uint startPos)
        {
            // TODO - What goes here?
            return "";
        }

        static void Main(string[] args)
        {
            byte[] value = new byte[] { 0x41, 0x42, 0x42, 0x42 };
            string result = GetText(value, 1);
            Console.WriteLine(result);
        }
    }
}

Expecting output: BBB

`.Length` - 1 will give you the last indexed value in an array. So if you are trying to convert bytes to characters and append it to a string, you could use a `for loop` starting at uint startPos and loop until `value.Length - 1` — Ryan Wilson, Aug 16 '18 at 16:55
@jdweng he wants to skip the characters until index is startPos, in this case 1, skipping the A — clcto, Aug 16 '18 at 16:55
Do you expect the 1 to refer to a byte offset, or a character offset? They may very well be different. — Jon Skeet, Aug 16 '18 at 17:03
In general, you might want to become familiar with LINQ, which has methods like `Skip` and `ToArray()` and `ToList()`. In this case : `value.Skip(startPos)` would return an enumerable of bytes from `startPos` to the end, then you would use standard byte-to-text conversion. — BurnsBA, Aug 16 '18 at 17:59

Attersson · Accepted Answer · 2018-08-16T17:05:26.837

5

string result =System.Text.Encoding.UTF8.GetString(value);
return result.Substring(startPos,result.Length-startPos);

(check that startPos is within 0 and length-1)

Or with GetString

return System.Text.Encoding.UTF8.GetString(value, startPos, startPos-value.Length);

edited Aug 16 '18 at 17:05

answered Aug 16 '18 at 16:56

Attersson

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5

you can also use the `GetString` override that accepts `index` and `count` arguments – St. Pat Aug 16 '18 at 16:58
Point made, edited. – Attersson Aug 16 '18 at 17:05
startPos-value.Length looks backwards, but I get the point. – Christopher Pisz Aug 16 '18 at 19:04

score 0 · Answer 2 · answered Aug 16 '18 at 16:59

I believe that you can achieve what you need with

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static string GetText(byte[] value, int startPos)
        {
            if(startPos >= 0 && startPos <= value.Length)
            {
               return System.Text.Encoding.UTF8.GetString(value).Substring(startPos);
            }
            else
            {
               return string.Empty;
            }
        }

        static void Main(string[] args)
        {
            byte[] value = new byte[] { 0x41, 0x42, 0x42, 0x42 };
            string result = GetText(value, 1);
            Console.WriteLine(result);
        }
    }
}

Array offset through end

2 Answers2