Comparing byte array with Hex values

[Shurikn]

this is pretty simple really... what i need is to compare some byte array obtain from the header of a file, to decimal value (to verify the signature) and unfortunatly, the 4 first byte of a jpg are not chars... they are plain hex value, wich Is why i need to do this, here's what I go so far:

if(entete.SOI!=0xFFD8)
		{
			return 0;
		}
		if(entete.JFIFMarker!=0xFFE0)
		{
			return 0;
		}

 

but the problem is that 0xFFD8 is seen as an integer and entete.SOI is a byte[2] so he wont compare them, so is there a way to:

1-change a byte array into integers

2-change an int into a byte array...

3 something else

[IngisKahn]

Sure there's a number of ways to do it. You can shift and or them together or better yet use a pointer to copy the value.

 

But the real question is why is SOI a byte array in the first place? It seems better suited to be an int or short. Generally you shouldn't expose arrays publically anyway.

[Shurikn]

well it's a structure so everything is just public in it...

puting it as a short is a good idea... that's what i'll do.

but just for my personal (and others) knowledge, how would you do it?

You can shift and or them together or better yet use a pointer to copy the value.

[IngisKahn]

Are you reading this from a stream? Just use BinaryReader.ReadInt16() in that case.

But anyway, here's 2 ways to convert a byte[2] array into a short:

short s = (short)((b[1] << 8) | b[0]);

or in an unsafe block:

fixed (byte* pb = b) s = *(short*)pb;

[Shurikn]

thanks, but just so someone reading this thread dont do mistake, using a short here wont work, because the value of 0xFFD8 =65496 and a shot stop at 32767, so a ushort (unsigned short) need to be used Edited June 9, 2005 by Shurikn

[IngisKahn]

Using short or ushort dosen't really make a difference. The short will just show up as a two's compliment negative number.