C# | Copy StringCollection at the specified index of array

StringCollection class is a new addition to the .NET Framework class library that represents a collection of strings. StringCollection class is defined in the System.Collections.Specialized namespace.

StringCollection.CopyTo(String[], Int32) method is used to copy the entire StringCollection values to a one-dimensional array of strings which starts at the specified index of the target array.

Syntax:

public void CopyTo (string[] array, int index);

Parameters:

• array : It is the one-dimensional array of strings that is the destination of the elements copied from StringCollection. The Array must have zero-based indexing.
• index : It is the zero-based index in array at which copying begins.

Exceptions:

• ArgumentNullException : If the array is null.
• ArgumentOutOfRangeException : If the index is less than zero.
• InvalidCastException : If the type of the source StringCollection cannot be cast automatically to the type of the destination array.
• ArgumentException : If the array is multidimensional or the number of elements in the source StringCollection is greater than the available space from index to the end of the destination array.

Note:

• The specified array must be of a compatible type.
• This method is an O(n) operation, where n is Count.

Below given are some examples to understand the implementation in a better way:

Example 1:

// C# code to copy StringCollection to array,
// starting at the specified index of
// the target array
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // creating a StringCollection named myCol
        StringCollection myCol = new StringCollection();

        // creating a string array named myArr1
        String[] myArr1 = new String[] { "A", "B", "C", "D", "E" };

        // Copying the elements of a string
        // array to the end of the StringCollection.
        myCol.AddRange(myArr1);

        // creating a String array named myArr2
        String[] myArr2 = new String[myCol.Count];

        // Copying StringCollection to array myArr2
        // starting from index 0
        myCol.CopyTo(myArr2, 0);

        // Displaying elements in array myArr2
        for (int i = 0; i < myArr2.Length; i++) {
            Console.WriteLine(myArr2[i]);
        }
    }
}

Output:

A
B
C
D
E

Example 2:

// C# code to copy StringCollection to array,
// starting at the specified index of
// the target array
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // creating a StringCollection named myCol
        StringCollection myCol = new StringCollection();

        // creating a string array named myArr1
        String[] myArr1 = new String[] {"1", "2", "3",
                                       "4", "5", "6"};

        // Copying the elements of a string
        // array to the end of the StringCollection.
        myCol.AddRange(myArr1);

        // creating a String array named myArr2
        String[] myArr2 = new String[myCol.Count];

        // Copying StringCollection to array myArr2
        // starting from index -1
        // This should raise exception "ArgumentOutOfRangeException"
        // as index is less than 0
        myCol.CopyTo(myArr2, -1);

        // Displaying elements in array myArr2
        for (int i = 0; i < myArr2.Length; i++) {
            Console.WriteLine(myArr2[i]);
        }
    }
}

Output:

Unhandled Exception:
System.ArgumentOutOfRangeException: Value has to be >= 0.
Parameter name: destinationIndex

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.specialized.stringcollection.copyto?view=netframework-4.7.2