really got stuck with unsigned chars

Hi,
I have program that converts 16 hex chars to 8-ascii characters
while testing, i have noted that the program generates a large unsigned chars figures such 266,239, 160...
How can I get the corresoonding ascii characters from above unsigned chars ?
here is the snippet:

Code:

---

code
 
/* prototype */
ByteType ASCIZ(ByteType *Addr);   

ByteType ASCIZ(ByteType *Addr)
{
        int i, v1, v2;
ByteType a1, a2, v,y;


        /* Convert 16-HEXA-character key to be 8-ASCII-character key. */
        for (i = 0; i < 8; i++)
        {
                a1 = *Addr++;
                if (i == 7)
                        a2 = *Addr;
        else
                        a2 = *Addr++;
                /* Convert two HEXA characters into their decimal value. */
                v1 = Convert(a1);
                v2 = Convert(a2);

       
      /* Convert the two decimal value to be one ASCII character. */
                v = ((v1 * 16) + v2);
        }
       
          return  v;
}



int Convert(ByteType val )
{
  if ((val >= 0  ) && (val <= '9' ))
       
      return val;         
 
  else ...
}

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Quote:

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Originally posted by Abdi
i have noted that the program generates a large unsigned chars figures such 266,239, 160...

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Unsigned char is 8 bits (0-255)...

Sorry, monster
it is 166 not 266, that was my error

That's right. 0-255. If the byte (char) is signed, then it is -127 to +127. That's because the high-bit is used to give sign. Otherwise, unsigned bytes (unsigned chars) are assumed positive.

What is the type of ByteType?

--

Testing can be done as follows, create a variable like this:

ByteType X [9] = "FFFFFFFF";

Then pass this to the function ASCIZ as follows:

ASCIZ (X);

--

In the function you are increasing the pointer. This is dangerous, better would be to have a local pointer in the function, called X_ptr or something, which points to the elements of the array. Or just use the indices of the array.

--

It seems you're having two hexadecimal values, like 0x05 and 0x06, which you want to combine into one ASCII character. 0x05 and 0x06 are between 0 and 9, so you add them to 16*5+6 = 86.
And that value is returned.

I do not really understand the purpose of the function. Can you give an example input with the correct output?

Hi shiro,

here is the desired effect.

if X = "3132333446474849", then I expect an output something like:

the corresponding characters are 0
the corresponding characters are 1
the corresponding characters are 2
the corresponding characters are 3
the corresponding characters are F
the corresponding characters are G
the corresponding characters are H
the corresponding characters are I

shiro you said use a local pointer X_ptr , I don't get what you mean ?

What Shiro means is: use a local pointer called X_ptr and let it point to Addr.
Then work with the X_ptr in stead of Addr.
This way the original pointer (Addr) is not changed.

Code:

---

ByteType ASCIZ(ByteType *Addr)
{
  ByteType *X_ptr = Addr;
  int i, v1, v2;
  ByteType a1, a2, v,y;

  /* Convert 16-HEXA-character key to be 8-ASCII-character key. */
  for (i = 0; i < 8; i++)
  {
    a1 = *X_ptr++;
    if (i == 7)
      a2 = *X_ptr;
    else
      a2 = *X_ptr++;
   
    /* Convert two HEXA characters into their decimal value. */
    v1 = Convert(a1);
    v2 = Convert(a2);

    /* Convert the two decimal value to be one ASCII character. */
    v = ((v1 * 16) + v2);
  }
  return  v;
}

---

The easiest way to solve this problem would be with a simple lookup table. Define a table of strings and hex-numbers like:

Code:

---

typedef struct
{
    char *string;
    int  hexvalue;
} string_hex_s;

string_hex_s string_hex_table [..] =
  {
  {"30", 0x30},
  {"31", 0x31},
  {"32", 0x32},
  {"33", 0x33},
  {"34", 0x34}
  ....
  };

---

Each time read two chars of the original string into a string, search for the string in the table and you find the hex-value immediately.

Another method, comparable to your method. Read two characters at once. Then use atoi to convert the string to integer and finally convert to hex-value.

Converting from decimal to hex can be done like the following example, the way you calculate it is not correct:

445 / 16 = 27 R 13
27 / 16 = 1 R 11
1 / 16 = 0 R 1

1= 1, 11 = B and 13 = D, so 445 = 1BD