Adding new items to string array

Question

I am trying to add 2 new array items to existing string array. I achieved the result but I am sure this is not the right way to do .

How can I add items to a string array.

string[] sg = {"x", "y" };    
string[] newSg = {"z", "w"};

string[] updatedSg = new string[sg.Length+newSg.Length];
for (int i = 0; i < sg.Length; i++)
{
    updatedSg[i] = sg[i];
}
for (int i = 0; i < newSg.Length; i++)
{
    updatedSg[sg.Length+i] = newSg[i];
}

Why don't you use `List`, or Linq `string[] updatedSg = sg.Concat(newSg).ToArray();` — L.B, Nov 01 '16 at 19:05

score 5 · Answer 1 · answered Nov 01 '16 at 19:11

You cannot add items to an array. You can use another container type, like a List, or you can create a new array with more elements and copy the old elements over. But you cannot add elements to an array and you cannot remove elements from an array. The number of elements in an array is fixed.

Dmitry Bychenko · Accepted Answer · 2016-11-01T19:16:24.953

You can Concat two arrays into one by using Linq:

 string[] updatedSg = sg
   .Concat(newSg)
   .ToArray();

An alternative is using List<String> for updatedSg collection type instead of array:

 List<string> updatedSg = new List<string>(sg);

 updatedSg.AddRange(newSg);

If you insist on updating an existing array then in general case you can have:

 // imagine we don't know the actual size 
 string[] updatedSg = new string[0];

 // add sg.Length items to the array
 Array.Resize(ref updatedSg, sg.Length + updatedSg.Length);

 // copy the items
 for (int i = 0; i < sg.Length; ++i)
   updatedSg[updatedSg.Length - sg.Length + i - 1] = sg[i]; 

 // add updatedSg.Length items to the array
 Array.Resize(ref updatedSg, newSg.Length + updatedSg.Length);

 // copy the items 
 for (int i = 0; i < newSg.Length; ++i)
   updatedSg[updatedSg.Length - newSg.Length + i - 1] = newSg[i];

In this case, how can be the scenarios where I have to update an item in the string array dealt? — Kurkula, Nov 01 '16 at 19:10

score 0 · Answer 3 · edited May 23 '17 at 10:27

0

Using CopyTo()

var updatedSg  = new string[sg.Length + newSg.Length];
sg.CopyTo(updatedSg, 0); 
sgNew.CopyTo(updatedSg, sg.Length);

As answered here https://stackoverflow.com/a/1547276/7070657

Or per somebody's suggestion:

var temp = x.Length;
Array.Resize(ref x, x.Length + y.Length); 
y.CopyTo(x, temp); // x and y instead of sg and sgNew

edited May 23 '17 at 10:27

Community

1
1

answered Nov 01 '16 at 19:10

brakeroo

1,407
13
24

In that case using [Array.Resize](https://msdn.microsoft.com/en-us/library/bb348051(v=vs.110).aspx) would be shorter code – UnholySheep Nov 01 '16 at 19:12
Also this should be `new string[]` not `new int[]` – UnholySheep Nov 01 '16 at 19:13
With Array.Resize it will still be 3 lines of code I believe. Can u do it in 2 lines of code? – brakeroo Nov 01 '16 at 19:15
`Array.Resize(ref sg, sg.Length + newSg.Length); newSg.CopyTo(sg, sg.Length);` is only two lines of code (reuses `sg` instead of creating a new variable) – UnholySheep Nov 01 '16 at 19:18
Did you try the above, you're changing the length of sg, exception is thrown "Destination array was not long enough. Check destIndex and length, and the array's lower bounds" This is how you fix it : var temp = x.Length; Array.Resize(ref x, x.Length + y.Length); y.CopyTo(x, temp); – brakeroo Nov 01 '16 at 19:25

score 0 · Answer 4 · answered Nov 01 '16 at 19:13

If i have to add items to an array dynamically, i would use a List instead of an Array (Lists have an Add() method very useful). You could even convert it to an array at the end of the process (with ToArray() method). But you can also use methods like Concat() as mentioned above.

Adding new items to string array

4 Answers4