C# string won't concatenate

Question

// Reads NetworkStream into a byte buffer.

NetworkStream ns;
System.Net.Sockets.TcpClient client = new TcpClient();

byte[] receiveBytes = new byte[client.ReceiveBufferSize];
ns.Read(receiveBytes, 0, (int)client.ReceiveBufferSize);
String returndata = Encoding.UTF8.GetString(receiveBytes);

I am successfully reading from a client and storing the result into a string called returndata. However, when I try to concatenate returndata with anything, no concatenation occurs. Ex: String.Concat(returndata, "test") returns returndata, as does returndata + "test".

Does anyone know why this is happening?

Edit: Steve W is correct; i found out later that returndata.Length was always returning 8192.

Would be better if you showed the actual code you are having trouble with. You've posted the code you've got working and neglected the code you haven't. — AnthonyWJones
– AnthonyWJones, Commented Feb 13, 2009 at 19:59
Agree with Anthony and Zach: why would you leave out the code that is causing the problems! — abelenky
– abelenky, Commented Feb 13, 2009 at 20:13

jhunter · Accepted Answer · 2009-02-13 19:56:03Z

5

Are you assigning it to a string or back to itself?

returndata = string.Concat(returndata, "test");
returndata += "test";

answered Feb 13, 2009 at 19:56

jhunter

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1 Comment

ShuggyCoUk Over a year ago

Psychic debugging - gotta love it :)

Mike Powell · Accepted Answer · 2009-02-13 20:22:46Z

5

To expand on jhunter's answer, the Concat method doesn't alter the contents of the original string variable, it just returns the concatenated result. If you want returndata to contain the result of the concatenation, you need to use returndata = string.Concat(returndata, "test").

edited Feb 13, 2009 at 20:22

answered Feb 13, 2009 at 19:59

Mike Powell

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2 Comments

abelenky Over a year ago

Its not just the Concat method, NO method directly modifies strings in C#. Every string is a unique, immutable object. If you change a string, it makes a new copy.

Mike Powell Over a year ago

That's true--bad choice of words on my part.

Steve Wranovsky · Accepted Answer · 2009-02-13 20:19:03Z

I believe the problem is related to not keeping track of the total number of bytes read. Your byte buffer, set to ReceiveBufferSize, is more than likely larger than the actual number of bytes read. By taking into account the actual bytes read, and then passing it to the Encoding.UTF8.GetString() method, you should get a valid string that can be concatenated. Here's an example:


NetworkStream ns;
System.Net.Sockets.TcpClient client = new TcpClient();

byte[] receiveBytes = new byte[client.ReceiveBufferSize];
int bytesRead = ns.Read(receiveBytes, 0, receiveBytes.Length);
String returndata = Encoding.UTF8.GetString(receiveBytes,0,bytesRead);
returndata = returndata.Trim(new char[] {'\0'});

Note also the other suggestion about reading a null terminator and including it in the bytes read also could be an issue. I've included a Trim of the string to make sure null terminators are removed.

Henk Holterman · Accepted Answer · 2009-02-13 19:58:57Z

3

I'll have a guess:

The received string includes a '\0' terminator. You ought to be able to check that with the debugger.

answered Feb 13, 2009 at 19:58

Henk Holterman

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4 Comments

Mike Powell Over a year ago

Excellent suggestion, considering the context. +1

Tanveer Badar Over a year ago

Wrong. Only C strings are null terminated.

Henk Holterman Over a year ago

@Tanveer: Yes, so what if the sender is a C/C++ program, that includes the '\0' ? .NET doesn't need the EOS char but can handle it - with results like tacogordito describes.

ShuggyCoUk Over a year ago

.net strings actually include a nul terminator, it's just that (by virtue of the length value) it can also include nulls as well (though it will no longer function as expected when passed to old style C functions via marshalling)

Frederik Gheysels · Accepted Answer · 2009-02-13 19:58:23Z

2

Strings are immutable. this means that, when you add (concatenate) another string to your string, you'll receive a new string instance.
The original string itself won't be changed.

answered Feb 13, 2009 at 19:58

Frederik Gheysels

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