Converting Between Different Number Bases

Environment: Win32, C++

Recently I was working on a project to store binary data to a text file and read it again. The solution I thought to be simple and fast was to convert each byte into hexadecimal format and then again convert it to binary format. There are other methods such as Base64 encoding to do it but I was short of time. So I created two functions fully UNICODE compatible.

The following functions convert to any number basis such as binary, octal, decimal, hex or in range of 2 to 36.

int
StrToNum(const TCHAR
*udata, int datalen,
int base) : 
Convert any string to relevant numerical  base.

TCHAR*
__fastcall NumToStr(TCHAR
*RetData, long number,
int base)  :
Converts any number to string in the desired base.

Here is the complete code with examples

#include <windows.h>
#include <iostream.h>
#include <tchar.h>

//convert the string to number
//udata is string
//udatalen is length of string
//base is numerical base eg. for decimal it is 10
// for hex it is 16
//largest base supported here is upto 36

int __fastcall StrToNum(const TCHAR *udata, int udatalen,  int base)
{
  long index;
  const TCHAR numdigits[] =   TEXT("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ");
  long digitValue = 0;
  long RetVal = 0;
  TCHAR digits[sizeof(numdigits)+1];
  TCHAR *dataVal;
  TCHAR data[512] ;

  //copy the data to our variable
  _tcscpy(data, udata);
  //convert it to upper case
  _tcsupr(data);
  ZeroMemory(digits, sizeof(digits));

  //copy the number of digits supported by          //base in digits
  _tcsncpy(digits, numdigits, base);

  for(index = 0; index < udatalen; index++)
  {
    //is the number there
    dataVal = _tcschr(digits, data[index] );
    if(dataVal != 0 )
    {
      //if it is subtract where to start point
      digitValue = long(dataVal - digits);
      //increment Retval with digitvalue
      RetVal = RetVal * base + digitValue;

    }
  }

  //return the result
  return RetVal;
}

TCHAR* __fastcall NumToStr(TCHAR *RetData, long number, int base)
{

  long index = 0;
  const TCHAR numdigits[] =  TEXT("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ");
  long digitValue = 0;
  TCHAR digits[sizeof(numdigits) + 1];
  TCHAR RetVal[512];
  TCHAR CurVal = 0;  

  ZeroMemory(RetVal, sizeof(RetVal));

  // only base supported are from 2 to 36
  if(base < 2 || base > 36 ) return NULL;

  ZeroMemory(digits, sizeof(digits));
  _tcsncpy(digits, numdigits, base);

  while(number)
  {
    digitValue = number % base;
    number = number base;
    RetVal[index++] = digits[digitValue];
  }

  //since string we have got is in reversed format
  //eg 100 will be 001 so we have to reverse it
  //and put the value in our variable

  ZeroMemory(RetData, _tcslen(RetVal)+1);

  int i = 0;
  for(index = _tcslen(RetVal) - 1; index > -1; index--)
  {
    //start reversing
    RetData[i++] = RetVal[index];
  }

  //return the result
  return RetData;

}

//our main function

int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{

  TCHAR Data[128];
  ZeroMemory(Data, sizeof(Data));

  //convert a number to string
  NumToStr(Data, 1123, 10);

  //now again convert string to number and see         //the result
  cout << StrToNum(Data, _tcslen(Data), 10) << endl;

  return 0;

}

Note: This code can also be used as a simple form of encryption. Here is a
simple eg.:-

//convert string "1024" to a number of base 10;
_tcscpy(Data, TEXT("1024") );
int Number = StrToNum(Data, _tcslen(Data), 10);
//convert the number to a different base 27;
NumToStr(Data, Number, 27);
//now check the number
cout << TEXT("Modified String is ") << Data << endl;
//now again get back our original number
Number = StrToNum(Data, _tcslen(Data), 27);
NumToStr(Data, Number, 10);
cout << TEXT("Original Number is ") << Data << endl;

That's All.

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