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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.

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Oh my god- so much code and for what??? Something that is already done with one line using "strtol" TheBishop 6:39 7 May '09   The whole concept of code reuse has been trampled upon. And for what??? What advantages does it bring? Here is one line solution: strtol({HEX_NUMBER_STRING}, NULL, 16) Sign In·View Thread·PermaLink 3.00/5 efficient & no library dependencies: tektor 13:04 15 Dec '08   unsigned int HexStringToUInt(char* s) { unsigned int v = 0; while (char c = *s++) { if (c < '0') return 0; //invalid character if (c > '9') //shift alphabetic characters down { if (c >= 'a') c -= 'a' - 'A'; //upper-case 'a' or higher if (c > 'Z') return 0; //invalid character if (c > '9') c -= 'A'-1-'9'; //make consecutive with digits if (c < '9' + 1) return 0; //invalid character } c -= '0'; //convert char to hex digit value v = v << 4; //shift left by a hex digit v += c; //add the current digit } return v; } Most of the branches can be eliminated (and thus any cost of their potentially failed prediction) with 'select' operations, depending on your processor. Sign In·View Thread·PermaLink dead horse c. leamon 5:08 11 Sep '07   not to beat a dead horse, but if you want to use this rather than some of the slower methods suggested by others, you can eliminate the use of the variable 'firsttime', since it's only used to eliminate shifting (<<4) on the first hex digit. That one shift is probably faster than the test for firsttime (occurs for every digit), and it's OK to shift unconditioinally since shifting those zeros has no affect on the results. Sign In·View Thread·PermaLink Why re-invent the wheel ? damnedyankee 2:10 8 Dec '06   stringstream ss; long val; ss << setbase(16) << "0xFDE8"; ss >> val; Sign In·View Thread·PermaLink 5.00/5 Re: Why re-invent the wheel ? Francesco Pratolongo 10:22 4 Apr '07   How beautyful is the Standard Library!!!!! Thank you, you save me a lot of time (and lines of code...) Sign In·View Thread·PermaLink 4.00/5 Shorter Code nfalabi 20:08 29 Oct '06   It can also be done like this: UINT HexToDec(const TCHAR *szValue) { UINT iValue; _stscanf(szValue, _TEXT("%x"), &iValue); return iValue; } I think it's much cleaner and simpler Sign In·View Thread·PermaLink 5.00/5 Re: Shorter Code as_sound_as 7:56 6 May '07   'swscanf' was declared deprecated you can use also CString s = _T("1A"); long k = wcstol( _T("0x") + s , 0, 0 ); Sign In·View Thread·PermaLink :) nice but... nicekr 5:12 14 Aug '06   what about 0x0000ea64 style? i try to convert hex string but return 0... nicekr Sign In·View Thread·PermaLink great!! KIM HyunJoong 20:05 3 Jul '06   good~~ gogogo!! Sign In·View Thread·PermaLink sscanf will do too ... Anonymous 4:08 27 Sep '05   CString hex_num("FDE8"); int dec_num; sscanf(hex_num,"%x",&dec_num); Sign In·View Thread·PermaLink 5.00/5 Re: sscanf will do too ... spinoza 16:53 4 Jan '06   this will also do but it is to slow.. bool CCoder::HexEncode(BYTE*pData,TCHAR*pCode) { TCHAR buffer[3]; BYTE b=*pData; if (b<16) { buffer[0]='0'; _itoa(b,buffer+1,16); }else _itoa(b,buffer,16); memcpy(pCode,buffer,2); return true; } bool CCoder::HexDecode(TCHAR*pCode,BYTE*pData) { TCHAR nr[3]; BYTE i; nr[2]='\0'; memcpy(nr,pCode,2); sscanf(nr,"%x",&i); *pData=i; return true; } //Spinoza Sign In·View Thread·PermaLink Thanks Codin' Carlos 20:58 16 Oct '02   It's 2am here. This converter did the trick. I didn't think about strtol either, but i can tell you i chaff at doing cstring.GetBuffer's etc, esp in unicode CE. Thanks for saving me a headache! Sign In·View Thread·PermaLink Re: Thanks Anonymous 6:00 17 Nov '04   Yep good job, remember that strtol only returns a long so easy to overflow! Change your _httoi to return dword/unsigned long, cheers! Sign In·View Thread·PermaLink Re: Thanks c4l 12:26 23 Apr '06   Thanks Anders, It works !!!!!!! Sign In·View Thread·PermaLink ;P If you speaking about C++ then this is the solution for converting a hexadecimal string to an integer Anonymous 3:19 12 Jun '02   I look on the net by 2 hours ago for thsi but I didn't found anything. Then I tried this: -char Str[]={"0x00f"}; -int n; -sscanf(Str,"%x",&n); now n is 15 And work. So simple. for converting a string to int then use atoi forint or atof for float SilverStar Sign In·View Thread·PermaLink 1.00/5 Use strtol. Anonymous 12:00 25 Jul '02   You guys ever try strtol.. Check it out.. you didn't have to write anything. Sign In·View Thread·PermaLink String to Int Komtiki 23:01 21 Apr '02   Nice peace of work. I found it very helpfull. Now can you tell me how can I can I convert a normal string to an integer. I have tried StrToInt but I cant get it to work. I don't know maybe I'm stupid but it says StrToInt Undeclared identifier. Can you help. Sign In·View Thread·PermaLink Re: String to Int Anders Molin 12:33 8 May '02   int i = atoi("55"); That does the trick... - Anders Money talks, but all mine ever says is "Goodbye!" Sign In·View Thread·PermaLink Try This also NMS 1:45 10 Aug '01   long BinfromHex(CString sz) { // This code is used to get the decimal value from given hexadecimal string long m_nbinVal=0; // stores the decimal value int cnt=0; for (int i = sz.GetLength()-1; i>=0; i--) { TCHAR psz; int val; lstrcpy(&psz,(LPCTSTR)sz.Mid(i,1)); // gets the one by one each character or numeric value and assign the according no switch (psz) { case 'A' : case 'a' : val = 10; break; case 'B' : case 'b' : val = 11; break; case 'C' : case 'c' : val = 12; break; case 'D' : case 'd' : val = 13; break; case 'E' : case 'e' : val = 14; break; case 'F' : case 'f' : val = 15; break; default : val = atoi(&psz); } m_nbinVal = m_nbinVal + long(pow(16,cnt) * val); // gets the according decimal value of hexadecimal value cnt++; } return m_nbinVal; // return s the converted value } Sign In·View Thread·PermaLink 5.00/5 Using CString again... Liqo 6:03 14 Mar '01   CString szHex = "FF"; int i = (int)strtol(szHex+'\n',(char **)NULL,16); Sign In·View Thread·PermaLink Slooooooow lookup Oz Solomonovich 7:33 17 Jan '01   You're using a lookup structure, but with a for() loop to scan through it! This is very inefficient. If you are already using a lookup, why not go all the way? Create a 256 entry lookup (actually less - you need only to go up to "f"), so, given a character you can do value = lookup[ch]; Another, more efficient way than you present is: if (isdigit(ch)) { value = ch - '0'; } else { value = (ch | 0x20) - 'a' + 10; } This is assuming valid input (i.e. no "g"'s in the input, etc.) -Oz --- Grab WndTabs from http://www.wndtabs.com to make your VC++ experience that much more comfortable... Sign In·View Thread·PermaLink 5.00/5 Another way -- using CString Paul Wolfensberger 6:32 14 Jan '01   // Convert a hexencode string to a "long" value // Only pass the hex "digits"...no symbols like "0x..." static long HexToLong(CString& szHexValue) { // Make the string a set of upper case, spaceless values szHexValue.MakeUpper(); szHexValue.TrimLeft(); szHexValue.TrimRight(); // Convert the digits number to values long lDigitCount = szHexValue.GetLength(); for (long lDigit=0, lValue=0; lDigit < lDigitCount; ++lDigit) { // Make a "space" for the next hex value lValue *= 16; // Now convert a single digit to a number TCHAR cDigit = szHexValue.GetAt(lDigit); if (cDigit >= '0' && cDigit <= '9') lValue += cDigit - '0'; else if (cDigit >= 'A' && cDigit <= 'F') lValue += 10 + cDigit - 'A'; else throw "Bad digit in Hex value string\nCStringConvert::HexToLong()"; } return lValue; } Sign In·View Thread·PermaLink std::stringstream Wilka 13:33 12 Jan '01   You could use std::stringstream, e.g. const char* str = "0xFF"; std::stringstream stream; stream << str; int n; stream >> std::hex >> n; assert(n == 255); Sign In·View Thread·PermaLink 3.50/5 Why don't you use strtol()? Nicolas P 12:07 12 Jan '01   There is a function in c to do that: #include long strtol(const char *nptr, char **endptr, int base); atoi(nptr) does the same as (int) strtol(nptr,(char **)NULL, 10). so just change the base (10 by 16) see the man page at: http://www.datafocus.com/docs/man3/strtol.3.asp Sign In·View Thread·PermaLink 5.00/5 Re: Why don't you use strtol()? William E. Kempf 12:35 12 Jan '01   Or sscanf or stringstream set for hex translation or... There are a million ways to skin this cat. Sign In·View Thread·PermaLink

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