Passing in null values to a recursive method

I have a method which I want to call itself if a certain condition is true. Initially the method accepts one parameter whose value changes before said condition is reached.

public static void Build(string str)
{
    var tree = XmlBuilder.Load();
    foreach (var section tree.Sections)
    {
        str += section.Name;
        foreach (var variable in tree.Sections[section].Variables)
        {
            //
        }
    }
    if (tree.Sections[section].Sections.Count >开发者_如何学Python 0)
    {
        // here I want to call Build(null)
    }
}

I'm not checking for a null value yet - just wanna know if this is possible first? If I say if (str==null) { } that wouldn't work because str has a value, correct? Is there any way of checking what value was PASSED IN to the method rather?

String is a reference type, so it can be null. Be aware that:

string str = null;
str += "foo";

// Now str == "foo"

If you do something like this you can preserve the original value passed into the method:

public static void Build(string str)
{
    string localStr = str;

    var tree = XmlBuilder.Load();
    foreach (var section tree.Sections)
    {
        localStr += section.Name;
        foreach (var variable in tree.Sections[section].Variables)
        {
            //
        }
    }
    if (tree.Sections[section].Sections.Count > 0)
    {
        // here I want to call Build(null)
    }
}

Just save it into another variable, before changing it. .NET has no way to get the passed in value of a parameter after it has been changed.

ou could send a 'null' to that function where str = null or you could check if it is = "" or String.Empty

Yes, you can pass in null as the parameter.

Then yo ucan check in the code if str == null, and put the required logic.