How much bytes are my data - TCP-String

[krivan]

Hi,

I have a 40960 elements long 1D array of SGL data type. I flatten it and I send it through TCP. The receiver gets it but certainly slower than it is sent. It makes me think that I read in much more bytes than needed. For the TCP read I use the CRLF option.

After flattening the 40960 long SGL 1D array should become a 40960 long string that would be 40960 bytes. Now, the TCP includes its data as well but I don't know how much, i.e. I don't know how much data [in bytes] I really send and so don't know how much to receive.

Thanks for the advices.

[GregFreeman]

Set up a header packet of a constant size, as shown below, which includes the length of the array you are sending. You get this length by typecasting the data to a string, then using the string length function to determine the array size in bytes. Using this method makes your code expandable, rather than using a constant for the number of bytes read on the host side.

Send 

Receive

[krivan]

Thanks!

After I posted I realised that the TCP Write contains a "byte written" output. That actually solved my problem.

[GregFreeman]

if you are using that to get the number of bytes then hardcoding this value, I would not recommend doing that. It will cause expandability issues for your code, and make it much more difficult if you change the data type you are typecasting to a string.

[altenbach]

I don't undrstand how the "bytes written" can solve your problem. The receiving end needs to know that, and that's elsewhere.

[GregFreeman]

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@altenbach wrote:
I don't undrstand how the "bytes written" can solve your problem. The receiving end needs to know that, and that's elsewhere.

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I believe what was done is the OP used an indicator to see the number of bytes written, then hardcoded this value as a constant on the host side. Bad, bad, bad, bad....,bad...........bad...............bad............

[PhillipBrooks]

A Single is 32 bits long. 

If you convert the array of single to a string using Type Cast, you should get 4 characters per single, or 163,840 characters.

If you write the contents of the array to a binary file, the file will also be 163,840 bytes in size.

Why do you think that the TCP string transmitted would be 40960 bytes long?

[GregFreeman]

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@Phillip Brooks wrote:

Why do you think that the TCP string transmitted would be 40960 bytes long?

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Single = single byte?

[krivan]

Hi,

yes, the hardcoding kills the expandability, true. And that it is bad bad bad is true as well, I'll change my code using the solution you suggested [very clever by the way!] a bit later however for the application at the moment all I needed was a quick fix.

So I got the "byte written" value of the sent TCP packet and hardcoded the value into the receiver side. 

Actually I knew that SGL is 4 bytes large but I somehow forgot that 4 bytes are 4 bytes in a flattened way as well. Hmm...