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Convert a "Hex String" to an Integer

By , 15 Jan 2001
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    Convert a "Hex String" to an Integer

    Sometimes I have had a string containing a Hex Value like char s[10] = "0xFDE8"; that I would like to convert to an integer (in this case it would of course get the value 65000). I have not been able to find any standard C or C++ functions to do that, so I decided to write my own. It's declared as _httoi(const TCHAR *value) and is coded using TCHAR so it works both with and without UNICODE defined

    It's possible it could be done smarter and faster, but it works and if you like it it's yours to use for free.

    Here is the code to a small console application that uses the function, and demostrates its use.

    #include "stdafx.h"
    #include <tchar.h>
    #include <malloc.h>
    
    int _httoi(const TCHAR *value)
    {
      struct CHexMap
      {
        TCHAR chr;
        int value;
      };
      const int HexMapL = 16;
      CHexMap HexMap[HexMapL] =
      {
        {'0', 0}, {'1', 1},
        {'2', 2}, {'3', 3},
        {'4', 4}, {'5', 5},
        {'6', 6}, {'7', 7},
        {'8', 8}, {'9', 9},
        {'A', 10}, {'B', 11},
        {'C', 12}, {'D', 13},
        {'E', 14}, {'F', 15}
      };
      TCHAR *mstr = _tcsupr(_tcsdup(value));
      TCHAR *s = mstr;
      int result = 0;
      if (*s == '0' && *(s + 1) == 'X') s += 2;
      bool firsttime = true;
      while (*s != '\0')
      {
        bool found = false;
        for (int i = 0; i < HexMapL; i++)
        {
          if (*s == HexMap[i].chr)
          {
            if (!firsttime) result <<= 4;
            result |= HexMap[i].value;
            found = true;
            break;
          }
        }
        if (!found) break;
        s++;
        firsttime = false;
      }
      free(mstr);
      return result;
    }
    
    int main(int argc, char* argv[])
    {
      TCHAR *test[4] = {_T("0xFFFF"), _T("0xabcd"), _T("ffff"), _T("ABCD")};
      for (int i = 0; i < 4; i++)
        _tprintf(_T("Hex String: %s is int: %d\n\r"), test[i], _httoi(test[i]));
      return 0;
    }
    

    Well, that's all there is to it. You can either copy the code from your browser, or download the project for Visual C++ 6.0.

    License

    This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

    A list of licenses authors might use can be found here

    About the Author

    Anders Molin
    Software Developer (Senior)
    Denmark Denmark
    Huh! Wink | ;-)

    Comments and Discussions

     
    QuestionLicense? PinmemberMember 896106510-Jul-12 2:50 
    GeneralInteger string (64bit) to hex having only 32 bit PinmemberRomanoScuri13-Sep-10 22:41 
    GeneralOh my god- so much code and for what??? Something that is already done with one line using "strtol" PinmemberTheBishop7-May-09 5:39 
    Generalefficient & no library dependencies: Pinmembertektor15-Dec-08 12:04 
    Generaldead horse Pinmemberc. leamon11-Sep-07 4:08 
    QuestionWhy re-invent the wheel ? Pinmemberdamnedyankee8-Dec-06 1:10 
    AnswerRe: Why re-invent the wheel ? PinmemberFrancesco Pratolongo4-Apr-07 9:22 
    GeneralShorter Code Pinmembernfalabi29-Oct-06 19:08 
    GeneralRe: Shorter Code Pinmemberas_sound_as6-May-07 6:56 
    'swscanf' was declared deprecated
     
    you can use also
     
    CString s = _T("1A");
    long k = wcstol( _T("0x") + s , 0, 0 );
     
    Smile | :)

    General:) nice but... Pinmembernicekr14-Aug-06 4:12 
    Generalgreat!! PinmemberKIM HyunJoong3-Jul-06 19:05 
    Generalsscanf will do too ... PinsussAnonymous27-Sep-05 3:08 
    GeneralRe: sscanf will do too ... Pinmemberspinoza4-Jan-06 15:53 
    GeneralThanks PinmemberCodin' Carlos16-Oct-02 19:58 
    GeneralRe: Thanks PinsussAnonymous17-Nov-04 5:00 
    GeneralRe: Thanks Pinmemberc4l23-Apr-06 11:26 
    General;P If you speaking about C++ then this is the solution for converting a hexadecimal string to an integer PinmemberAnonymous12-Jun-02 2:19 
    GeneralUse strtol. PinsussAnonymous25-Jul-02 11:00 
    GeneralString to Int PinmemberKomtiki21-Apr-02 22:01 
    GeneralRe: String to Int PinmemberAnders Molin8-May-02 11:33 
    GeneralTry This also PinmemberNMS10-Aug-01 0:45 
    GeneralUsing CString again... PinmemberLiqo14-Mar-01 5:03 
    GeneralSlooooooow lookup PinmemberOz Solomonovich17-Jan-01 6:33 
    GeneralAnother way -- using CString PinmemberPaul Wolfensberger14-Jan-01 5:32 
    Generalstd::stringstream PinmemberWilka12-Jan-01 12:33 

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