Help! Reading in hex values from file to unsigned char in C.

[JonTheBaller]

I have a file called "input.txt". Within input is a string of hexadecimal values:

a7b38fd9cb24a38de31729... (etc)

I want to read in the values as bytes, rather than ASCII characters. So for the example above, I would want to read in the form:

{ 0xa7, 0xb3, 0x8f, 0xd9, 0xcb, ... }

This seems like a pretty simple thing to do, but I'm stuck. Please help!

Thanks!

 

[JonTheBaller]

Maybe I should be specifying that the file is a binary file? Or should I be using %x in my fscanf() line?

 

[JonTheBaller]

help! 🙁

 

[EmperorRob]

What functions are you using to open/close/read from this file?

 

[Barnaby W. Füi]

Use c++ and boost::lexical_cast 😉

I googled and within 10 seconds (this is why STFW is in my sig 😉) found this

 

[JonTheBaller]

Originally posted by: BingBongWongFooey
Use c++ and boost::lexical_cast 😉

I googled and within 10 seconds (this is why STFW is in my sig 😉) found this

Well I'm using C, not C++.

 

[JonTheBaller]

Originally posted by: EmperorRob
What functions are you using to open/close/read from this file?

Rob, I figured out my problem. I simply read in the characters as ASCII, and if it was in the range 0-9 I subtracted 48 (48 == '0'); if it was in the range a-f I subtracted 87 (97 == 'a'). That gets me two half bytes (nybble?). Then I bit shift the first half-byte 4 bits, and or it with the second half-byte.

I thought there might be a more "seamless" method of doing this.

 

[Barnaby W. Füi]

Originally posted by: johnnytightlips

Originally posted by: BingBongWongFooey
Use c++ and boost::lexical_cast 😉

I googled and within 10 seconds (this is why STFW is in my sig 😉) found this

Well I'm using C, not C++.

That's what the winky face is for.

Seriously, I found that solution in a few seconds of googling; I'm sure you can find a nice solution with a little more searching.

 

[EmperorRob]

Originally posted by: johnnytightlips


Rob, I figured out my problem. I simply read in the characters as ASCII, and if it was in the range 0-9 I subtracted 48 (48 == '0'); if it was in the range a-f I subtracted 87 (97 == 'a'). That gets me two half bytes (nybble?). Then I bit shift the first half-byte 4 bits, and or it with the second half-byte.

I thought there might be a more "seamless" method of doing this.

I would read the file as text. I just got through figuring out how to do this in perl so I got curious. What I wound up having to do is read the hex values in as strings and prepend an 'x' to them then sprintf with %x.