C# foreach iterating rule for collections

How .NET decides for order of items when iterating through collections ?

For example:

list<string> myList = new List<string>();

myList.Add("a");
myList.Add("b");
开发者_开发技巧myList.Add("c");

foreach (string item in myList)
{
    // What's the order of items? a -> b -> c ?
}

I need this order (accessing collection members):

for (int i = 1; i < myList.Count; i++)
{
    string item = myList[i - 1]; // This is the order I need
}

Can I safely use foreach with List? What about other types of collections?

.NET doesn't decide it - the class implementing IEnumerable decides how it is being done. For List that is from index 0 to the last one. For Dictionary it depends on the hash value of the key I think.

List indexes are 0 based, so you can do this:

for (int i = 0; i < myList.Count; i++)
{
    string item = myList[i]; // This is the order I need
}

and is the same result as foreach. However if you want to be explicit about it then just stick to the for loop. Nothing wrong with that.

I believe foreach starts at the first index and steps though until the last item in the list.

you can safely use foreach although I think it is a little slower than the for i=1; i < myList.count method.

Also, I would say you usually start at index 0. eg:

for (int i = 0; i < myList.Count -1 ; i++)
{   
 string item = myList[i]; // This is the order I need
}

foreach is fine . You should only look into the internals of how a loop works if you are looking for perfomance ( eg a number cruncher ) .

Don't worry, use foreach.

list myList = new List();

myList.Add("a");
myList.Add("b");
myList.Add("c");

foreach (string item in myList)
{
    // It's in right order! a -> b -> c !
}

A generic List will enumerate in the order of addition, as you suggest. Other implementations of Enumerator may vary, If its important you could consider a SortedList.