C# - Using Memory Streams with XML [modified]

[Ostrich22]

I have come across an interesting problem. If I have a DataSet which I've read from an XML file. Then I call WriteXML to my memory stream. If I try read it back into a dataset I get the following error "Root Element is missing" here is some example code. DataSet ds = new DataSet(); ds.ReadXmlSchema(@"C:\Foo\FooSchema.xsd"); ds.ReadXML(@"C:\Foo\Foo.xml"); MemoryStream ms = new MemoryStream(); ds.WriteXml(ms); ds.ReadXml(ms); //Error occurs. Does anyone know why? or how I can use a DataSet to read directly from a MemoryStream?

modified on Tuesday, October 20, 2009 9:58 AM

[Keith Barrow]

The current position pointer of the memory stream is left at the end when you do the ds.WriteXml. You have to do something (apologies, no access to IDE right now) like ms.CurrentPosition = 0; before the the ReadXml to move it back to the start.

CCC solved so far: 2 (including a Hard One!)

[Covean]

In your example you try to read after the written data (MemoryStream position != 0). You have to reset the read position of the memory stream.

MemoryStream ms = new MemoryStream();
ds.WriteXml(ms);
ms.Seek(0, SeekOrigin.Begin);
ds.ReadXml(ms);

[Ostrich22]

Aah yes, silly me, I forgot about the pointer. Thank you!

[OriginalGriff]

Keefb is coirrect, you have to rewind the stream, using:

if (ms.CanSeek)
{
ms.Seeek(0,SeekOrigin.Begin);
}

But be aware it may not work! You may well need ms.FlushFinalBlock() to ensure that last bit of data is written.

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[Mirko1980]

If you look at the value of ms.Position after you have wrote in it, you'll see that has the same value of ms.Length. That is because you have just written into the stream and the stream cursor is located at the end. Due to that, if you try to read the stream content, the reader doesn't found anything to read, giving the "Root Element is missing" exception. Call ms.Seek(0, SeekOrigin.Begin) (or set ms.Position = 0) to move the cursor back to the beginning of the stream after writing and before reading.

[Luc Pattyn]

if all else fails, maybe try and set ms.Position=0; :laugh:

Luc Pattyn

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