Need a Dummies Guide to Parsing Data

normschaef

All:

I know my long-time friend and colleague Eric Medley may jump in and answer this question, but all answers are welcome.

After many years away from control systems, I've moved positions and now need to maintain some in our Engineering College. In December I was in Chicago for Programmer 1 which I thoroughly enjoyed.

I could use some help in parsing text. I want to get the position information from my cameras in a distance classroom. I'm using a Buffer to dump the data coming from the codec (Cisco C90). My question is how to get started pulling out the PTZF information. I need to populate an array of camera positions because a puny 15 presets in the codec won't cut it. I need to turn it up.

Here's what my buffer shows me:

xStatus Camera 1 Position *s Camera 1 Position Focus: 4608 *s Camera 1 Position Pan: 352 s* Camera 1 Position Tilt: 34 *s Camera 1 Position Zoom: 687 ** end

I need each of those integers for my table.

From my search of the forum, I headed to TechNote 616, but I'm still baffled as to how to pull those PTZ numbers out.

And Eric.... It's fun to be back programming and overseeing distance learning classrooms again

Norm Schaeffer
Learning Spaces Project Manager
University of Nebraska - College of Engineering

DHawthorne

I'm not familiar with that codec, so anyone who is can chime in with corrections if I made any invalid assumptions.

It looks to me like the * character is pretty consistent and an end-of-field. You can tokenize it with a loop that breaks out each segment before the star. I'd do it something like this:

DEFINE_FUNCTION fnCodecParse()
{
     STACK_VAR sToken[255] // Adjust size up or down based on the maximum field size, or assign it to a constant
    
     WHILE(FIND_STRING(sBuffer, "'*'",1))
     {
          sToken = REMOVE_STRING(sBuffer, "'*'",1)) ;
          // Process sToken here
     }    
}

For your process token segment, it's going to matter how the codec spits out the feedback. If it sends the same data every time, in the same order, you can put a counter on your loop that just assigns the values based on what order it came in. If the fields vary, you can use a SELECT...ACTIVE to search for an identifier and break it out that way. In either case, you can just do a series of ATOI's on your sToken string; it will ignore the non-numeric values and make an integer out of the rest. First pass would give you your camera number. Then do a REMOVE_STRING built on the camera number to strip that out, and your second pass will be the actual parameter value.

ericmedley

Hey Norn! I'm so very excited to hear you're programming again and better yet on the forum. This is a great group of people who love programming and are extremely helpful. Dave is awesome!

To amplify on Dave's comment...

I'd think of the string this way, almost like an XML file:

xStatus // This is a status message
  Camera 1 Position *s  // This is a Status message of type: Position from Camera 1
    Camera 1 Position Focus: 4608 *s 
    Camera 1 Position Pan: 352 s* 
    Camera 1 Position Tilt: 34 *s 
    Camera 1 Position Zoom: 687 
** end

So, I might do something like this. I'm leaving out a buch of stuff I wo0uld also do - but this hopefully will cover enough to explain.

DEFINE_DEVICE

dvCam_01=5001:01:0

DEFINE_CONSTANT

integer cam_ct=3;  // for 3 cameras
(***********************************************************)
(*              DATA TYPE DEFINITIONS GO BELOW             *)
(***********************************************************)
DEFINE_TYPE

structure _MyCams{
integer	Focus
integer	Pan
integer	Tilt
integer	Zoom
	}
(***********************************************************)
(*               VARIABLE DEFINITIONS GO BELOW             *)
(***********************************************************)
DEFINE_VARIABLE

volatile _MyCams MyCams[cam_ct];

volatile char MyCam_Buffer[200];

volatile char Cam_Return_Name[][25]={
	{'xStatus'} // all the different possible return types.
	,{'xSomethingElse2'}
	,{'xSomethingElse3'}
	}



define_function fn_Parse_The_String(char buffer[200]){
	stack_var integer command_id;
	stack_var integer nloop;
	stack_var integer cam_id;
	// this section checks what type of return - in this case xStatus
	for(nloop=length_array(Cam_Return_Name);nloop;nloop--){ // finds the return type
		if(find_string(buffer,Cam_Return_Name[nloop],1)){
			command_id=nloop;
			break // we've found the command
			} // if
		} // for(
	
	// this section parses
	switch(command_id){
		case 1:{  // xStatus return
			remove_string(buffer,'Camera',1) // strips off string up to first "Camera"
			cam_id=atoi(buffer);  // get which cam it is.
			if(cam_id){ // if we do indeed have a cam id
				remove_string(buffer,'Focus:',1);
				MyCams[cam_id].Focus=atoi(buffer);
				remove_string(buffer,'Position Pan:',1);
				MyCams[cam_id].Pan=atoi(buffer);
				remove_string(buffer,'Position Tilt:',1);
				MyCams[cam_id].Tilt=atoi(buffer);
				remove_string(buffer,'Zoom:',1);
				MyCams[cam_id].Zoom=atoi(buffer);
				// now go do something with all these new values.
				} // if cam _id
			} // case
		case 2:{  // xSomethingElse2 return
			// parse for this return type
			} // case
		case 3:{  // xSomethingElse3 return
			// parse for this return type
			} // case
		} // swithc(command_id)

	}

DEFINE_EVENT

data_event[dvCam_01]{
	string:{
		MyCam_Buffer="MyCam_Buffer,data.text"
		while(find_string(MyCam_Buffer,'**',1)){ // or whatever the end of message is
			fn_Parse_The_String(remove_string(MyCam_Buffer,'**',1));
			}
		}
	}

So, first - In the data_event we keep building the string up until we get the end charactors. You will probably get all this in one chunk anyway. But, it's always a good idea to build it yourself just in case the message gets broken up into more than one data_event. There are many ways to do this kind of thing. This is just one. Once we hafve our whole message in MyCam_Buffer we pass it into the function's buffer, clear out our main buffer and run off to parse.

Next - we run up to our function called fn_Parse_The_String() with our message in its buffer. The first thing we do is determine what type of return it is. In our case it is a Status message, but it could be other things. I made up silly names for the other things but you'd put the real names there. The for loop runs through our array of possible return names looking for a match. Once it finds it we populate the variable command_id with the id number of the array. (in our case it's list item (1) so nloop will equal `1. We're done int he loop so we break out. No point in continuing. bear in mind that if we don't find the type of message return we just command_id will equal zero. so we won't parse and will fall through the next section without parsing anything.

Next (step 3) - we go to the Switcch/Case stack and search for the code to parse a xStatus message (case 1).
First thing is to determine whichc camera we're getting the message from (Camera 1 in this case). we just remove the text in front of the first "Camera 1" by remvoe_string "Camera" that will leave the 1 which we can convert to an integer by ATOI(bufffer)

The If(cam_id) statemnet is a catchall to prevent us from trying to do a Camera 0 if we get goofy data or whatnot.

the remove_string(buffer,'Focus:',1); statement takes up to the space just after the "Focus:' in the buffer which leaves the buffer saying "4608 *s Camera 1 Position Pan: 352 s* Camera 1 Position Tilt: 34 *s Camera 1 Position Zoom: 687 ** end"

we just need to do another atoi() to get the value into our structure.
MyCams[cam_id].Focus=atoi(buffer);
so MyCams[1].Focus=4608

We just need to keep chopping our way through the string until we have all our values. Once done we can then do something with them like update feedback or make evaluations about what to do with the values, etc...

There's a whole host of stuff on managing the buffer/queue, command structures and all that. but, this example, hopefully, expalins the basics of it. For esxample, I would really try and granularize the individual value returns since they all contatin the Camera 1 header. it's more than likely you'd get several cameral IDs stomping all over each other at once. This example assumes that the message comes in nice order one cam at a time.

I will try and call you soon!
Be well and God bless!
Eric