Having a mental block....need help

Projects Programming
1

Guys I am having the mother of all mental blocks.

I am trying to base64 encode a string with this code:

void CSerialManager::encodeASCII(CString &strData)
{
CBuff<128> buffEncoded;
CBuff<4> buffHex;
CString strEncoded(buffEncoded), strHex(buffHex);
uint8_t nHex = 0;
debug.log(F(""));
for (uint8_t nI = 0; nI < strData.length(); nI++)
{
if (isAlphaNumeric(strData[nI]))
{

if (isUpperCase(strData[nI]))
{
nHex = uint8_t(strData[nI]) - uint8_t('A');
}
else if (isLowerCase(strData[nI]))
{
nHex = uint8_t(strData[nI]) - uint8_t('a') + 26;
}
else if (isDigit(strData[nI]))
{
nHex = uint8_t(strEncoded[nI]) - uint8_t('0') + 52;
}
strHex.format("%02X", nHex);
strEncoded += strHex;
debug.log(strData[nI]);
debug.log(uint8_t(strData[nI]) - uint8_t('0') + 52);
debug.log(nHex);
debug.log(strEncoded);
debug.log(F("-------"));
}
else
{
strEncoded += strData[nI];
}
debug.log(strData[nI]);
debug.log(strEncoded);
debug.log(F("-------"));
}
strData = strEncoded;
}

Here is my debug output in Serial monitor:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Serial Communication Out

Sending to HC-05 = 1/6
1.........debug.log(strData[nI]); from "1/6"
53.......debug.log(uint8_t(strData[nI]) - uint8_t('0') + 52) CORRECT FROM THE BASE64 ALPHABET
4.........debug.log(nHex); HOW DID 53 decimal end up as 4 decimal?
04.......debug.log(strEncoded);
-------.. debug.log(F("-------"));
1
04

/
04/

6
58
51
04/33

6
04/33

~
04/33~

04/33~
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

1/6 is the input string.

I am using the base64 alphabet from here:
https://www.garykessler.net/library/base64.html

53 decimal is the result of converting an ascii '1' to a base64 alphabetic string using the above table.
And it is correct - 53 is the code for ASCII '1' in base64

What I can't get my head around is HOW 53 decimal ends of as 4 decimal with this

nHex = uint8_t(strEncoded[nI]) - uint8_t('0') + 52;

2

boylesg:
else if (isDigit(strData[nI]))
{
nHex = uint8_t(strEncoded[nI]) - uint8_t('0') + 52;
}

3

IT appears to be something to do with the way I have implemented the string indexing function my class CString:

class CString
{   

     inline char& operator [](const int16_t nI)
    {
      return m_pBuff->m_strBuffer[nI];
    }
};

Essentially the following is doing something strange: uint8_t(char&).

But for the life of me I still don't understand it!

m_strBuffer is a regular 'C' string.

My class CString code is attached.

CString.cpp (26.7 KB)

CString.h (9.86 KB)

4

arduarn:

That won't help - I am building strEncoded from nHex

strHex.format("%02X", nHex);
strEncoded += strHex;

5

boylesg:
That won't help - I am building strEncoded from nHex

strHex.format("%02X", nHex);
strEncoded += strHex;

Oh what an idiot! What you pointed out just dawned on me! Thanks