Convert a base 60 ID stored as string back to int : C++, string

May 9, 2008 06:23am pdt

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03.26.2008 at 07:47AM PDT, ID: 23270567

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9.3

Convert a base 60 ID stored as string back to int

Zones: C++ Programming Language, C Programming Language, Microsoft Visual C++

Tags: C++, string

Hi,

See the attached function. I would like to have another function that will reverse the process - it would ignore the first nInitials chars, and then compute the correct int value of the remaining string, 0's being ignored (place holders).

The function below takes a string, a numeric value and a length and returns a string assembled with them. So if I will pass "DK", 3, and 8 it will return "DK000003", and for "DK", 10, and 8 "DK00000a".

I would want to avoid the use of STL/MFC.

Stilgar.

         
           
           
             LPCTSTR GenerateArticleID(LPCTSTR pInitial,DWORD dwNum, DWORD dwSize, LPTSTR pBuf) {
		TCHAR buf[64];
		DWORD dwPad = dwSize - _tcslen(pInitial);
		_itot(dwNum,buf,36);
		DWORD dwLen = (DWORD)_tcslen(buf);
		if (dwLen + _tcslen(pInitial) > 8) return NULL;
		_stprintf(pBuf,_T("%s%0*.*s"),pInitial,dwPad,dwPad,buf);
		return pBuf;
	}

           
         

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Question Stats

Zone: Programming

Question Asked By: _Stilgar_

Solution Provided By: itsmeandnobodyelse

Participating Experts: 1

Solution Grade: A

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03.26.2008 at 09:27AM PDT, ID: 21213380

Rank: Genius

itsmeandnobodyelse:

You may take the below. It compiles but I didn't tested it.

         
           
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             bool getArticleNumAndSizeFromId(LPCTSTR szArticleId, 
                                LPTSTR szArticle, DWORD dwArticleSiz, 
                                DWORD & dwNum, DWORD & dwSiz)
{
   dwSiz        = _tcslen(szArticleId);
   DWORD dwOff  = _tcscspn(szArticleId, "0123456789abcdef");
   if (dwOff == 0 || dwOff >= dwSiz) 
         return false;   // no hex digits
   char* sentinel = NULL;
   dwNum = _tcstol(&szArticleId[dwOff], &sentinel, 16);
   if (sentinel == NULL || *sentinel != '\0') 
      return false;  // non-digits stopped conversion
   if (dwArticleSiz <= dwOff)
      return false;  // buffer given is too small
   _tcsncpy(szArticle, szArticleId, dwOff);
   szArticle[dwOff] = TCHAR(0);
   return true;
}
           
         

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03.26.2008 at 09:33AM PDT, ID: 21213462

_Stilgar_:

Err... This is not a base 60 code (my bad) but rather base 36 (10 digits + 26 letters). My intention is to have g-z computed as well. So this is not a Hex value as well....

Will this work for my case?

Stilgar.

03.26.2008 at 10:19AM PDT, ID: 21214024

Rank: Genius

itsmeandnobodyelse:

>>>> Err... This is not a base 60 code (my bad)
No, it was my fault. I didn't recognize the base60.

You may use the following code

...
dwSiz = _tcslen(szArticleId);
LPTSTR ptsz = _tcschr(szArticleId, TCHAR('0'));
if (ptsz == NULL) return false;
DWORD dwOff = (DWORD)(ptsz - szArticleId);
if (dwOff == 0 || dwOff >= dwSiz)
return false; // no '0' character
char* sentinel = NULL;
_tcstol(&szArticleId[dwOff], &sentinel, 36);
...

though I actually never used a base greater 16.

Note, checking for a range of 36 'digits' doesn't make so much sense as the article code is alpha as well. Hence I checked for a '0' char only cause you can't restore the tokens if not at least one '0' was inserted as a filler.

03.26.2008 at 01:37PM PDT, ID: 21215938

_Stilgar_:

I'm not sure why you are looking for a 0? What if I have a code of length 3, which has 2 letters as initials, so it looks like "DKc" ? What I need is to pass an int value which will be used to skip over the initials (I will normally pass 2, but this might change), and then the code should skip all 0's until the first alphanumeric char, and then begin conversion.

Also, can you please post the full function? I'm not sure where to paste the above (not that noob, just not to concentrated atm...).

Thanks.

03.27.2008 at 12:51AM PDT, ID: 21219301

Rank: Genius

itsmeandnobodyelse:

>>>>> I'm not sure why you are looking for a 0?
If both the 'number' and the prefix consist of alphabetic letters, how will you decide where the one begins and the other ends?

If the base 36 digits were small letters only (is it?) and the prefix only has capital letters we could go for that?

03.27.2008 at 02:47AM PDT, ID: 21219741

_Stilgar_:

>>>> If both the 'number' and the prefix consist of alphabetic letters, how will you decide where the one begins and the other ends?

By using nInitials. If >0, then skip the nInitials first letters and start converting from there. I will always know how many initials were used, by definition (and even if I didn't, I could do the scan for the first 0 on my own before calling this function).
Anyway, the article ID is case insensitive.

I hope this makes sense to you now. If not please let me know.

Stilgar.

03.27.2008 at 02:52AM PDT, ID: 21219760

_Stilgar_:

The function signature should be something like:

int GetArticleNumber (int nInitials, LPCTSTR szArticleID)

szArticleID is the string holding the ID, nInitials would be the number of characters to skip (the initials) in the string.

Stilgar.

03.27.2008 at 04:32AM PDT, ID: 21220222

Rank: Genius

itsmeandnobodyelse:

int GetArticleNumber (int nInitials, LPCTSTR szArticleID)
{
char* sentinel = NULL;
int num = (int)_tcstol(&szArticleID[nInitials], &sentinel, 36);
if (sentinel == NULL || *sentinel != TCHAR('\0'))
return -1; // non-digits stopped conversion
return num;
}

Accepted Solution

03.27.2008 at 08:35AM PDT, ID: 21222505

_Stilgar_:

Thanks, that seems to do the job (still testing). How could the sentinel == NULL after _tcstol (it should be TCHAR* btw)?

Stilgar.

03.27.2008 at 10:40AM PDT, ID: 21223962

Rank: Genius

itsmeandnobodyelse:

>>>> How could the sentinel == NULL
It shouldn't. But I generally was testing pointers returned by functions on NULL before accessing them. In case of a NULL pointer dereferencing by *sentinel would cause an access violation.

03.27.2008 at 10:52AM PDT, ID: 21224088

_Stilgar_:

In that case, you should have made the if statement to be a two-stage check; in its current form it will AV as well if the pointer was NULL...

Sorry about digging into this, but I'm new to _tcstol :)

Stilgar.

03.27.2008 at 10:58AM PDT, ID: 21224154

Rank: Genius

itsmeandnobodyelse:

>>>> in its current form it will AV as well

No, an if condition is guaranteed to be processed from left to right. If the left expression of a logical or (||) is true, the right expression will not be evaluated.

03.27.2008 at 11:06AM PDT, ID: 21224222

Rank: Genius

itsmeandnobodyelse:

>>>> but I'm new to _tcstol :)
The _tcstol is the "T" version of strtol, i. e. it either was mapped to strtol in case of ANSI strings or to wcstol in case of UNICODE strings.

strtol - contrary to atoi - can convert numbers of different bases *and* checks for the character that terminates conversion. The sentinel would point to the first position within the char array passed in which wasn't a valid digit (within the range of digits defined by the base given). That should be the terminating zero character or something was wrong.

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