String To Hex

[Bengi]

hi all,

is there a fast way to make a String, ie: chat str[]="2E5F1D"
transform to an hex number with same value, i.e: DWORD hexnum=0x2E5F1D, ?
thnx all

[cup]

There is a fast way but it is *VERY* expensive in terms of space.

// initialization
DWORD lookup[256];
memset (lookup, 0, sizeof (lookup));
lookup['0'] = 0;
lookup['1'] = 1;
..
lookup['A'] = 10;
...
lookup['F'] = 15;
lookup['a'] = 10;
...
lookup['f'] = 15;

// conversion of str
DWORD value = 0;
for (int i = 0; str[i]; i++)
    value = (value << 4) | lookup[str[i]];

Basically anything outside the range is 0. So 123XYAF would convert to 12300AF. I only use it if time is a critical issue.

[zdf]

I'm sure the code below is not the best solution. However is faster than others. I hope it'll help you.

//-------------------------------------------------------------------------
/*
No white
No checking: the string must be a hex number
*/
unsigned int htoi(const char* s)
{
  static unsigned int h[256] = { 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  0,  0,  0,  0,  0,  0, 
    0, 10, 11, 12, 13, 14, 15,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0, 10, 11, 12, 13, 14, 15,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0
  };
  unsigned int t = 0;
  while ( *s ) 
  {
    t <<= 4;
    t += h[*s++];
  }
  return t;
}

int main()
{
  unsigned int i = htoi("2E5F1D");
  return 0;
}

Regards,

[cup]

Both zdf and I have the same solution: it is just the initialization that is different.

[stober]

The simple solution is to use sscanf()


char str[]="2E5F1D";
DWORD hexnum;
sscanf(str, "%x", &hexnum);