BCD conversion

[dyingatmidnight]

Hello all, I'm trying to modify some code but I'm having some difficulty - probably because I don't really understand the function in the first place. Its one my supervisor found online that seemed to work fine for the purposes of our test code. However; after some poking around its not working entirely as I need it to, so I was going to modify it. Only to find I really have no idea how to modify it to accomplish what I need.

Here's the downloaded function:

////////////////////////////////////////////////////////////////////////////////
// FUNCTION : atobcd
// ARGUMENTS: pBcd      - (output) void pointer to location where the encoded
//                                 text number will be written.
//            nBcdLen   - (input)  usable length of the pBcd variable.
//            pszNumber - (input)  pointer to a char array containing the text
//                                 representation of the number to encode.
//            nNumLen   - (input)  length of the input pszNumber char array.
// RETURNS  :  0 - Success
//            !0 - Error
// PURPOSE  : Converts an ASCII (text) representation of a number to BCD. 
//            (Binary Coded Decimal)
////////////////////////////////////////////////////////////////////////////////
int CTestDPDlg::atobcd(void* pBcd, int nBcdLen, char* pszNumber, int nNumLen)
{
	int nError = 0;
	int i      = 0;  //INDEX TO INPUT ASCII REPRESENTATION OF THE NUMBER
	int j      = 0;  //INDEX TO BCD REPRESENTATION OF THE NUMBER

	

	

	char szSingleNumberAscii[2]  = {0};
	char nSingleNumberBinary     = 0;

	char* pBcdVal = reinterpret_cast<char*>(pBcd);
	
	
	

	//LOOP UNTIL END OF ASCII NUMBER OR END OF BCD REACHED
	while(i < nNumLen && j < nBcdLen)
	{
		memset(szSingleNumberAscii, 0, sizeof(szSingleNumberAscii));
		nSingleNumberBinary = 0;

		szSingleNumberAscii[0] = pszNumber[i];
		nSingleNumberBinary    = atoi(szSingleNumberAscii);
		
		
		if(!(i%2))
		{
			pBcdVal[j] = nSingleNumberBinary << 4;
		}
		else
		{
			pBcdVal[j] += nSingleNumberBinary;
			j++; //INCREMENT EVERY OTHER ITERATION OF THE LOOP
		}
		
		
		i++; //INCREMENT EVERY ITERATION OF THE LOOP
		
	}

	return nError;
}

And we're using it in this fashion:

value.Remove('.');
atobcd(positionSSBL->zPosRawByteArray, 3, value.GetBuffer(),  value.GetLength());

if zPosRaw = 1234.5 the array looks like this:

zPosRawByteArray[0] = 0x12
zPosRawByteArray[1] = 0x34
zPosRawByteArray[2] = 0x50

and what I need is:

zPosRawByteArray[0] = 0x01
zPosRawByteArray[1] = 0x23
zPosRawByteArray[2] = 0x45

The digit in the tens position needs to be the LSB. I think its just a matter of changing the atobcd so it goes backwards? But I'm afraid I'm so new to C++ that I'm not really grasping the function properly, even stepping through it I find its hard to really understand what's happening.

[Narue]

Have you tried prepending a '0' to the string before converting it?

[dyingatmidnight]

umm, oooh! why didn't I think of that. Or well actually I had but in the non-mfc version of this I did myself I was using integers and totally forgot this version of the application is using strings, so adding a zero shouldn't be hard. *tries*

[dyingatmidnight]

Actually having looked it all over again I realize that, while that solution works for this particular example it won't for others. My arrays are fixed. Like for the position values x, y and z they are supposed to take up 3 bytes. Basically if the value of x were 50.0 then the resulting array should be:

[0] = 0x00
[1] = 0x05
[2] = 0x00

instead I get

[0] = 0x50
[1] = 0x00
[2] = 0x00

[Narue]

That makes no difference. If the arrays are fixed, the strings should be fixed as well to conform to your arbitrary idea of how bytes should be distributed. The same solution of zero padding will work.

[dyingatmidnight]

Yes, thank you, that does work. Had to give it more than a moments thought :D

[m4ster_r0shi]

Excuse me, this is not homework, right? Why not do it the STL way?

#include <iostream>
#include <string>
#include <bitset>

using namespace std;

string atobcd(const string & ascii)
{
    string ret;

    string::const_iterator cur_it = ascii.begin();
    string::const_iterator end_it = ascii.end();

    for ( ; cur_it != end_it; ++cur_it)
        ret += bitset<8>(*cur_it - '0').to_string(); // uncompressed representation
     // ret += bitset<4>(*cur_it - '0').to_string(); //       packed representation

    return ret;
}

int main()
{
    string ascii;

    while (true)
    {
        cout << "enter a number: ";

        getline(cin, ascii);

        if (ascii == "") break;

        cout << atobcd(ascii) << endl;
    }
}