Buffer to integers

Posted on 2003-10-28
Last Modified: 2013-12-14
I have a buffer which contains hex numbers

e.g ff 22 5f 4f 4f ff 4a 6a aa ff 9a 9b af .....etc

I want to copy each of the hex numbers from the buffer in turn, to an integer.
int numa = 0xff;
int numb = 0x22;
int numc = 0x5f;
int numd = 0x4f;  
int nume = 0x4f; ...and so forth

I need the code to be efficient please,

Question by:XPUSR
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Expert Comment

ID: 9637329
This buffer is a array of hex numbers? or is a string?

Post the declaration of that buffer please.


Author Comment

ID: 9637502
char * buffer;
buffer = (char*) malloc (10000);
fgets ( buffer, 1000,"file.txt" );
the buffer is a string of hex values(without the 0x) "ff 22 5f 4f 4f ff 4a 6a aa ff 9a 9b af ". These values are taken from a text file "file.txt" and copied to the buffer.

sorry for being so ambiguous...

LVL 19

Assisted Solution

Dexstar earned 75 total points
ID: 9637764

> I want to copy each of the hex numbers from the buffer in turn, to an integer.

Try this:

      int GetHexValue( char chr )
            switch( toupper(chr) )
            case '0': return 0x00;      break;
            case '1': return 0x01;      break;
            case '2': return 0x02;      break;
            case '3': return 0x03;      break;
            case '4': return 0x04;      break;
            case '5': return 0x05;      break;
            case '6': return 0x06;      break;
            case '7': return 0x07;      break;
            case '8': return 0x08;      break;
            case '9': return 0x09;      break;
            case 'A': return 0x0A;      break;
            case 'B': return 0x0B;      break;
            case 'C': return 0x0C;      break;
            case 'D': return 0x0D;      break;
            case 'E': return 0x0E;      break;
            case 'F': return 0x0F;      break;
            default:  return 0;            break;

      // lpszChars = Array of Chars to Convert
      // pInts = Array of Ints to Hold Converted Values
      // nSize = # of Ints to Convert
      void ConvertHex( char* lpszChars, int* pInts, size_t nSize )
            char*      lpCurrent = lpszChars;
            for ( unsigned register nCounter = 0 ; nCounter < nSize ; ++nCounter )
                  pInts[nCounter] = (GetHexValue(*(lpCurrent++)) << 8) |

Just allocate the array of integers that you want to convert, and then ConvertHex().

Hope that helps,
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LVL 15

Expert Comment

ID: 9638446
Or you could let the library do more of the work:

#include <sstream>

using namespace std;

istringstream iss(buffer);
// Tell iss to interpret numbers as hexadecimal.
iss.setf(ios::hex, ios::basefield);

iss >> numa;
iss >> numb;
//  etc.


Accepted Solution

EarthQuaker earned 75 total points
ID: 9638754
Developping efn's path of stopping wheel's reinvention :

#include <algorithm>
#include <sstream>
#include <vector>

const char* buffer="ff 22 5f 4f 4f ff 4a 6a aa ff 9a 9b af";
istringstream ss(buffer);
ss >> hex;
vector<int> v;
copy(istream_iterator<int>(ss), istream_iterator<int>(), back_inserter(v));

cout << "Item 1 is " << v[0] << endl;
LVL 19

Expert Comment

ID: 9643280
Well, those are good too... I just wanted to give him a solution where it was very clear what was going on and how it worked.  You start invoking the STL like that on someone who doesn't know it, and they will find it difficult to learn how you did what you did.


Expert Comment

ID: 9644031
Dex : Nothing wrong with your solution, it's prolly faster.

I just tend to use something premade & robust & fast instead of doing all by hand.

Author Comment

ID: 9708505
Thanks both solutions work 100%, appreciate that you were trying to explain it....


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