Which ASCII character to send

[MasterDucky]

I want to send only one character to the other side to signal that there was an error.

I'm looking for a character that never appears in a file.

I looked at the ASCII chart and I thought maybe:

- 127 177 7F 01111111  Delete
or
- 129 201 81 10000001

http://www.ascii-code.com/

[VictorN]

ASCII character 0x81 is the small u umlaut. See http://www.theasciicode.com.ar/
DEL character (127) can be used by some OS for special purposes. See http://en.wikipedia.org/wiki/ASCII and http://en.wikipedia.org/wiki/Delete_character

[MasterDucky]

Thank you Victor.

Looks like the DEL character should be OK on Windows.

[2kaud]

I'm looking for a character that never appears in a file.

Depends somewhat upon whether a file is type 'text' or 'binary'. In a binary ASCII file any of the characters from 0 to 255 may appear. In a 'text' file 1 - 6, 14 - 26, 28 - 31 and 255 are unlikely to occur.

[MasterDucky]

It's for binary too so maybe just one character is not the best solution.

Thanks Kaud, that's what I wanted to know.

[Codeplug]

You could base64 encode the file contents, then use a NAK (21) (or whatever) in your protocol.

gg

[2kaud]

It's for binary too so maybe just one character is not the best solution.

Thanks 2Kaud, that's what I wanted to know.

What are you trying to achieve? If you are using binary files then any sequence of one or more characters could possibly occur in any file.

[MasterDucky]

What are you trying to achieve? If you are using binary files then any sequence of one or more characters could possibly occur in any file.

Thats true.

I would like to signal to the other side that an error occurred and dont wait for the file.

[MasterDucky]

You could base64 encode the file contents, then use a NAK (21) (or whatever) in your protocol.

Base64 doesnt use all the ASCII characters?

[VictorN]

I want to send only one character to the other side to signal that there was an error.
I'm looking for a character that never appears in a file.

How do you "send" your file?

[MasterDucky]

How do you "send" your file?

Windows TCP/IP Send() function.

[2kaud]

If all you want to do is to signal an error from the send side, what about just closing the connection? This will be picked up by recv() as an error for which you can test. If you want to resend then the sender can re-open the connection etc.

[MasterDucky]

You could base64 encode the file contents, then use a NAK (21) (or whatever) in your protocol.

gg

This looks like the best solution.

[VictorN]

Also look at the shutdown function in MSDN.

Besides, this thread is a very good example of how one should NOT ask the question.
The more reliable question about your problem should have looked like:

I send a file through a TCP socket.
If some error occured on the sender side, what should I do or what should I send to the receiver to inform that send operation is broken?

Then you would have got the valuable answer in some minutes, not in 11 hours!

[MasterDucky]

Yes, but I want to know if it was an error with the connection or with some other operation, like couldn't open a file I asked for or anything else.