binary comparison

This is a discussion on binary comparison within the C Programming forums, part of the General Programming Boards category; hi all... i have a small program that reads an image char by char in binary mode. so the output ...

  1. #1
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    binary comparison

    hi all...

    i have a small program that reads an image char by char in binary mode. so the output looks like :

    <FF> 1
    <D8> 2
    <FF> 3
    <E1> 4
    ^W 5
    { 6
    E 7
    x 8
    i 9
    f 10
    ^@ 11
    ^@ 12
    M 13
    M 14
    ^@ 15
    * 16
    ........

    i need to make sure that the first char - here above as <FF> - is always at the start of the file. sometimes it isn't. so i need to look for the <FF>. in order to find it i was told to look for 0xFF. but when i do the comparison as in (c == 0xFF ) is not doing it.

    here is what i got:
    Code:
    int main (int argc, char *argv [])
        {
          FILE * fhin = fopen (argv[1], "rb");
            char c;
            int i = 1;
    
          while (fread (&c, 1, 1, fhin) ) {
            if ( c == 0xFF) printf("%s\t", "moo");
             printf("%c\t%d\n", c, i++);
          }
         
          fclose (fhin);
    
    
          return (0);
        }

    what would be the correct way?

    thanks..

  2. #2
    Registered User whiteflags's Avatar
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    Signed chars have a sign bit, which is either on when the byte, interpreted as a number, is negative. When the sign bit doesn't matter you should be using unsigned chars. Of course, all signed chars fit in an unsigned char, so that is not a problem to worry about, either.

  3. #3
    ATH0 quzah's Avatar
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    The problem here is that char can be either signed or unsigned. It's implementation specific. If you need an unsigned value, then use an unsigned type.


    Quzah.
    Hope is the first step on the road to disappointment.

  4. #4
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    Quote Originally Posted by quzah View Post
    The problem here is that char can be either signed or unsigned. It's implementation specific. If you need an unsigned value, then use an unsigned type.


    Quzah.
    got it. thanks...

  5. #5
    Algorithm Dissector iMalc's Avatar
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    Just make sure that the things on both sides of the equals sign are the same type.
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