jermore

When sending an integer using MScomm's .Output function I'm assuming it sends the entire length of the data type, is that correct?

For example,

Dim X As Integer
Dim Y As Long

X = 3
Y = 3

comPort.Output = X 'sends 00000000 00000011
comPort.Output = Y 'sends 00000000 00000000 00000000 00000011

Or is the value truncated? I am trying to read in a binary file and send it using the code below, but I need to send the file size first and the receiver end will be expecting 4 bytes regardless of whether the file size is 1 or 10,000 bytes. Any suggestions? Feel free to critique the code below in regards to sending the file.

Dim FF As Integer
Dim strOpen As String
Dim strBuff As String

dlgOpenFile.ShowOpen
strOpen = dlgOpenFile.FileName
FF = FreeFile()

Open strOpen For Binary As FF

strBuff = String(LOF(FF), " ")

Get FF, , strBuff
frmMain.comPort.Output = strBuff

Close FF

mkaras

Using either of these sequences is NOT the way to send the length of the file. The comPort.Output function accepts a String or a Byte Array as its output value. So one of the assignments that you show is not allowed.

In order to get a string value and to work out getting the converted number value into a string that is always the same length you could consider something like this:

Here I show how you intentionally convert the Y variable value to a string that has a length of 12. So you know you will send 12 characters out the comm port.

By the way, if you were to range check the value of Y to be less than the full range of the value stored in a Long you could use a shorter template string in the Format statement. For example if you made sure that 0 <= Y <= 255 then the template string could be "000" with length 3 and you would know you send 3 bytes.

There are ways to manipulate sending the actual binary value of the Long variable. It involves separating the 32-bits of the variable into four bytes and then sending each of those bytes as a string byte to the port. However I would recommend the method shown here here for a couple of reasons. First off it is easy be able to read the file length in transmitted data sequence if it has been formatted to human readable format. Secondly, you only send the value once so there is little or no performance issue if you send four bytes or twelve. And on the receiving end it is very easy to accumulate the first 12 bytes into a string and convert that back into a long value using the CLng() function.

passel

If you have a binary file you need to send, you wouldn't normally read it into a string array, as it will be converted into unicode (two bytes in the string for each byte read from the file). When transmitted out the serial port, it will probably be serialized as ASCII (one byte per char), but I haven't worked with string data in or out of a serial port in a long time, only binary data structures, so can't say definitively.
It is much faster (and half the memory), to read the file into a binary array, and send that through the port. The CopyMemory API call is what I usually use to copy structures (user defined types) to and from byte arrays.
It can also copy a Long, to the first 4 bytes of a byte array, to be sent out the port.