Hex to ASCII in c

Question

Here is my logic, to convert HEX to ASCII conversion in C:

for (i=0;i<ArraySize;i++)
    {
        /*uses a bitwise AND to take the top 4 bits from the byte,
         0xF0 is 11110000 in binary*/
        char1 = Tmp[i] & 0xf0;
        char1 = char1 >> 4;
        /*bit-shift the result to the right by four bits (i.e. quickly divides by 16)*/
        if (char1 >9)
        {
            char1 = char1 - 0xa;
            char1 = char1 + 'A';
        }
        else
        char1 = char1 + '0';
        Loc[j]=char1;
        j++;
        /*means use a bitwise AND to take the bottom four bits from the byte,
        0x0F is 00001111 in binary*/
        char1 = Tmp[i] & 0x0f;
        if (char1 >9)
        {
            char1 = char1 - 0xa;
            char1 = char1 + 'A';
        }
        else
        char1 = char1 + '0';
        Loc[j]=char1;
        j++;
        Loc[j]=0;
    }

Temp and Loc are string buffers. Defined and has data. It is not working properly. I am reading data in temp from some file (sample fread). It stop reading file at particular point. If I change first

0xf0

to

0x0f

Here is how file is being read:

BytesRead = fread (Tmp,1,Bytes,PrcFile);

Then it reads whole file. I am not able to find what is missing. Can you please help me in this regards. Thanks

Can you show the code that does the file reading/writing? The algorithm looks correct. — , Feb 10 '12 at 11:46
Add the code for reading the file and for the constuction of the arrays. — Ed Heal, Feb 10 '12 at 11:47
Your question is too confusing: ASCII is a number, and thus already an hex, no need to convert anything. Also in your title you put hex to ASCII, and in the heading ASCII to Hex... Can you please explain with an example what you want to do... — m0skit0, Feb 10 '12 at 11:49
I want to read a hex file and show its information in ASCII. — QMG, Feb 10 '12 at 11:55
Loc is like this 'char unsigned loc[4000];' and 'char unsigned temp [2500];' — QMG, Feb 10 '12 at 12:03
To explore further possibilities i think we need your whole code. As in a sscce.org — Bernd Elkemann, Feb 10 '12 at 12:44
Thanks eznme.But me prepare sample and then I will see what is sscce. We will further explore there. — QMG, Feb 10 '12 at 12:51

Ed Heal · Answer 1 · 2012-02-10T12:36:44.893

2

This is not an answer but an observation - using this since it formats code

static char lookup[] = { '0', '1', '2','3','4','5','6','7','8','9','A','B','C','D','E','F' };
int j = 0;
for (i=0; i<ArraySize; ++i)
{
   loc[j++] = lookup[(Tmp[i] & 0xf0) >> 4];
   loc[j++] = lookup[Tmp[i] & 0xf];
}
loc[j] = 0;

makes the code a lot quicker and simpler.

edited Feb 10 '12 at 12:36

answered Feb 10 '12 at 11:57

Ed Heal

59,252
17
87
127

Thanks Ed for your input. let me do in this way and may be something change. – QMG Feb 10 '12 at 11:59
1

Ooh - make sure that the length of `loc` is (at least) 2 * ArraySize + 1 – Ed Heal Feb 10 '12 at 12:04

score 0 · Answer 2 · answered Feb 10 '12 at 12:08

0

Even though Ed already provided a shorter solution, i tried to figure out what was wrong because your code "looked" correct.

Let me guess: char1 is signed (e.g. type "char").

It then happens, that:

a byte in your file that is >127 keeps its sign during &0xf0,
and >> 4 is a signed shift which makes the bit-pattern keep the bit set in the most significant bit
then you compare >9 which is not the case because the sign-bit is still set
then you add +'0' which can now lead to you having a byte with value 0 instead of something between '0'-'9' or 'A'-'F'.
which terminates the string while printing

answered Feb 10 '12 at 12:08

Bernd Elkemann

23,242
4
37
66

Yes, that seemed to be the problem. Try your code and change the declaration of `char1` to `unsigned char`. – Bernd Elkemann Feb 10 '12 at 12:23
I tried to run it on different files but it reads same number of bytes from files and them stop. No matter file size is 30 K or 100K – QMG Feb 10 '12 at 12:23
How many characters are read? Is the two arrays of the correct lengths? – Ed Heal Feb 10 '12 at 12:33
Ed, I have run you code it is also behaving the same as my old code. It reads exactly 16384 bytes no matter what is the size of file. [for sure file should be greater than this number of bytes]. Actually I have setup to read different number of bytes base upon setup defined. It reads 16382 characters correctly and then it reads only 2 character, although I asked to read 29 characters. – QMG Feb 10 '12 at 12:45

Hex to ASCII in c

2 Answers2

Linked