What is the difference between IEnumerable and Foreach loop

Khaja Moizuddin

Can anyone explain me the difference between the both, when should I use IEnumerable and Foreach loop, as both are used for looping the collections.

9 Replies

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Nitin Sontakke9y ago
Hello,

I am not the expert on the subject, however, to the best of my knowledge when you start iterating, your pointer is NOT at the first element but before that. Which you can say is a ghost position. You cannot access any data at that time.

This is similar to SqlDataRead.Read() where the first call reads the first record, if found otherwise returns false.

So in this case first .MoveNext() reads the first element, second second and third third. After that it returns false and loop terminates. The execution of first .MoveNext method makes the first element Current.

To gain excellent understanding of this (and many other) concepts, please do see Jamie King's C# videos on YouTube. Really very good and helpful.
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Khaja Moizuddin9y ago
Gnanavel I have a little confusion in Movenext method, see the below code using System.Collections.Generic; class Program { static void Main() { List list = new List(); list.Add(1); list.Add(5); list.Add(9); List.Enumerator e = list.GetEnumerator(); Write(e); } static void Write(IEnumerator e) { while (e.MoveNext()) { int value = e.Current; Console.WriteLine(value); } } } We are getting output as 1,5,9 If in a list we have 3 elements say 1,5,9. When performing e.MoveNext(), it will check the next element in the collection,on first element it will check 2ND element ie.5, on 2ND element it will check next element ie.9, on 3rd element it will check next element in the collection hence condition fails, then how we are getting output as 1,5,9 Can anyone explain me this.
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Saravanan Ponnusamy9y ago
Simple

IEnumerable is a Collection of data

foreach is a iteration of data's or iteration of collection's

eg:

foreach (string File in Directory.EnumerateFiles(FilePath, "*.csv"))//enum is a collection and foreach for iteration
{

}

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Gnanavel Sekar9y ago
Hi Khaja,
The cost of allocating the enumerator object by entityList.GetEnumerator().
The cost of two virtual methods calls (MoveNext and Current) for each element of the list.
IEnumerable.GetEnumerator() returns an enumerator object (which implements IEnumerator). This has a property "Current" which returns the current item, and a method "MoveNext()" which advances the enumerator on to the next item.

This is all the foreach loop needs to perform the foreach. It simply assigns the "Current" property to a variable then executes .MoveNext() each time.

Usually, when you implement IEnumerable on a class, you know where the source is coming from. So if you had a class such as this
public class MyEnumerable { private List items; }
The implementation of IEnumerable would look like this
public class MyEnumerable : IEnumerable
{
private List items;
public IEnumerator GetEnumerator()
{
return items.GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return items.GetEnumerator();
}
}
Notice that the enumerator is coming from the list object so you don't have to worry about creating an enumerator (though you can if you need to by implementing IEnumerator)

For More

https://stackoverflow.com/questions/21470793/what-is-the-link-between-foreach-and-ienumerable
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Sundaram Subramanian9y ago
IEnumerable is used to hold the Data (Collect Data)

Foreach is used to Iterate the Collected Data.
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Gokhul Varman9y ago
Refer the link for more detailed explantion you can get a clear solution:https://stackoverflow.com/questions/44220/difference-between-foreach-and-for-loops-over-an-ienumerable-class-in-c-sharp
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Amit Gupta9y ago
Long and detailed answer can be found on the below link
http://www.c-sharpcorner.com/UploadFile/0c1bb2/ienumerable-interface-in-C-Sharp/

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/foreach-in

Hope you understand the difference
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Khaja Moizuddin9y ago
Hello Amit gupta , i am not clear with your answer can you explain me with your small example , in which situation i need to use IEnumerator / IEnumerable compared to Foreach loop ?
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Amit Gupta9y ago
Short answer
IEnumerable is a collection of data

Whereas foreach loop is used to iterate the collection in a foreward only process.
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