State machine parser

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December 7th, 2012, 10:57 PM

ChokolAwt

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Join Date: Jan 2007

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State machine parser

Hello all,

For my final homework assignment our instructor has us writing a simple byte parser. the attached file (which needs to be renamed *.bin) is the input. For some reason, my parser seems to be grabbing something at the end of the file and passing it to my parse() method thus outputting junk at the end.

The input has a standard format of

Code:

Start->Type->Size(low)->Size(high)->Payload->Checksum

Theres 4 different Types for the input file (ASCII, Integer, Float and Double) but I'm just working on ASCII right now.

my parser class:

Code:

#include "parser.h"

parser::parser()
{
	this->State = start;
	i = 0;
	j = 0;
}

parser::~parser()
{

}

bool parser::parse(unsigned char byte)
{
	switch(this->State)
		{
			case start:
				if (byte = 170)
					{
						Chk = 170;
						State = type;
						break;
					}
				
				
			case type:
				Type = byte;
				Chk += byte;
				State = size_low;
				break;
					
			case size_low:
				Size = byte;
				Chk += byte;
				State = size_high;
				break;	
				
			case size_high:
				Size += (byte << 8);
				Chk += byte;
				State = payload;
				break;
				
			case payload:
				if (i == Size)
					{
						State = checksum;
						break;
					}
					
				Data[i] = byte;
				Chk += byte;
				i++;
				break;
				
			case checksum:
				if (byte = Chk) 
					{
						State = start;
						return true;
					}
				else 
					{
						State = start;
						break;
					}
		}
	return false;
}


void parser::process(void)
{
	switch(Type)
		{
			case 0:
				char *pa;
				pa = (char*)(Data);
					for(j; j < Size; j++)
						{
							std::cout << *pa << std::endl;
							*pa++;
						}
					
			case 1:
				int *pb;
				pb = reinterpret_cast<int *>(Data);
				for(j; j < Size; j++)
						{
							std::cout << *pb;
							*pb++;
						}
						
			case 2:
				float *pc;
				pc = reinterpret_cast<float *>(Data);
				std::cout << *pc;

			case 3:
				double *pd;
				pd = reinterpret_cast<double *>(Data);
				for (j; j < Size; j++)
					{
						std::cout << *pd;
						*pd++;
					}	
		}
}

my header file:

Code:

#include <iostream>
#include <string>

// Definition for Magic numbers
#define MAX_SIZE 1024

// ParseState are the different states in your parser 
enum ParseState{start, type, size_low, size_high, payload, checksum};

// The different types of payload
enum TypeID{asciiType, integerType, floatType, doubleType};

// Parser class definition
class parser{

	private:
		
		ParseState State;				// Holds the current state of the parser
		int i;
		int j;
		unsigned int Size; 				// Holds the size of the payload
		unsigned char Type;				// Holds the type of the payload
		unsigned char Chk;				// Holds the running checksum
		unsigned char Data[MAX_SIZE];	// Holds the payload data
		
		
	public:
		// Constructor
		parser();
		
		// Destructor
		~parser();
		
		// Parse function, 
		// Argument is a byte out of the input file
		// Return value is true when packet has been completely parsed and checksum is correct
		bool parse(unsigned char);
		
		// Process payload function
		void process(void);
		
};

and my main:

Code:

#include <fstream>
#include "parser.h"

using namespace std;


int main (int argc, char *argv[])
{
	ifstream filename;
	parser funk;
	unsigned char byte;
	
	//if user calls program from cmd prompt incorrectly
		if((argc < 2)) 
			{
				cout << "This program will parse a .bin file and print payload\n";
				cout << "\n";
				cout << "Usage: hw8 [input filename].bin\n";
				exit(0);
			}
	
	filename.open(argv[1], ios::binary); //open file in binary mode
		if ( !filename )
			{
				cout << "File does not exist.\n";
				exit(0);
			}
	
	while (!filename.eof())
		{
			byte = filename.get();
			//cout << "byte :" << hex << (int)byte << endl;
			if (funk.parse(byte) == true)
				funk.process();
		}
	filename.close();
}

When you run it at command line with

Code:

hw8 testASCII.bin

The output is

Code:

Hello World!1.14314e+027

The only thing I can think is that my while loop in my main is passing something to parse() that it shouldn't but I haven't been able to figure out why. Am I not using reinterpret_cast correctly?

Attached Files

testASCII.txt (17 Bytes, 22 views)

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December 7th, 2012, 11:34 PM

ChokolAwt

The bad and the ugly...

Join Date: Jan 2007

Location: Oz... No??? Neverland then?

Posts: 142

Time spent in forums: 1 Day 6 h 21 m 2 sec
Reputation Power: 0

headway!

Okay, so if i modify my while loop in main to print out byte each time through

Code:

while (!filename.eof())
		{
			byte = filename.get();
			
			cout << "byte :" << hex << (int)byte << endl;
			if (funk.parse(byte) == true)
				funk.process();
		}

The output is

Code:

 
byte :aa
byte :0
byte :c
byte :0
byte :48
byte :65
byte :6c
byte :6c
byte :6f
byte :20
byte :77
byte :6f
byte :72
byte :6c
byte :64
byte :21
byte :13
byte :ff
c
Hello world!1.14314e+027