comparison is always true due to limited range of data type BUT ITS NOT ALWAYS TRUE

[a1drich]

smartCryptor.cpp: In function `void Char2Hex(unsigned char, char*)':

smartCryptor.cpp:188: warning: comparison is always true due to limited range of data type

void Char2Hex(unsigned char ch, char* szHex)
{
 
   unsigned char byte[2];
   byte[0] = ch/16;
   byte[1] = ch%16;
 
   for(int i=0; i<2; i++)
   {
      if(byte[i] >= 0 && byte[i] <= 9)
         szHex[i] = '0' + byte[i];
      else
         szHex[i] = 'A' + byte[i] - 10;
   }
 
   szHex[2] = 0;
 
   }

may somebody explain why compiler gives this even though its not always true. or am i missing something?

thanks,
Aldrich

[Ganon11]

In your if statement, you write:

if (byte[i] >= 0 && byte[i] <= 9)

but perhaps you should be comparing with the characters '0' and '9' rather than the values 0 and 9:

if (byte[i] >= '0' && byte[i] <= '9')

[AdrianH]

In your if statement, you write:

if (byte[i] >= 0 && byte[i] <= 9)

but perhaps you should be comparing with the characters '0' and '9' rather than the values 0 and 9:

if (byte[i] >= '0' && byte[i] <= '9')

No, what the OP posted is correct. This has to do with the byte being unsigned. An unsigned variable cannot be less than zero. Thus your expression byte[i] >= 0 will always be true.

Signed and unsigned values mess up a lot of people. I'm not special, I've just had a lot of exposure with them. Had to write a library that did things like sign extention and not depending on the type it was assigned in a C DB, just because of this reason (long story).


Adrian