Thread: Converting Numeric Characters to Hex

Also, a character its just a 2 byte (or 1 byte) variable. It has to do with size. Hex is just how you translate a value from the basic binary format (maybe not a good terminology here).
So you have to know what type of variables Wii uses. I am saying this because a file will just be a 00101010010101010...1000101 thing. If you read one, one byte or two two bytes or whatever depends the type you tell it to read. If you tell to read an 4 byte int it will read 4 bytes and store them in a memory space and tag them as a int.

So you can do as suggested and substract '0'. Also a char uses ' ' and not " "

And isn't char 1 byte?

And I have no idea how you get 0x30 from casting it to an int

Thanks for your help.

Hmm, well I tried the subtract '0' thing, but I got an error "cannot convert char to char". Here is the code I was trying to use:

Code:

         ofstream output ( argv[argc-1], ios::out | ios::trunc | ios::binary );
         PacHeader[0] = '\0';
         strcat ( PacHeader, "ARC" );
         output.write (PacHeader, 3);
         output.seekp( 0x07 );
         argv[2] = argv[2] - '0';
         output.write ( argv[2], 1);
         output.seekp( 0x40 );

As for what the Wii will read, the file is pretty basic.

Main header:
0x00 [4] = 'ARC\0'
0x06 [2] = Number of files (3 = 0x0003, 15 = 0x000F, etc)
0x10 [48] = File name

File header:
0x04 [4] = Size of file
0x20 = File data

Anything else isn't important and can just be filled with null bytes. I can get it to write everything else, since it is all either copied from another file or is already a string of characters, however since this one byte must be user entered, it can't be written as entered since it will give the hex value of 3 (0x33) rather than the byte 0x03. I know I'm still not explaining it well, but I don't know how else to put it.

Code:

         PacHeader[0] = '\0';
         strcat ( PacHeader, "ARC" );

can bet written as

Code:

         strcpy ( PacHeader, "ARC" );

Code:

         output.write (PacHeader, 3);

Does not match:

Code:

0x00 [4] = 'ARC\0'

as the latter is 4 bytes, and you write 3 bytes.

My guess is that:
"cannot convert char to char"
should be
"cannot convert char* to char"
since you are trying to do that in this line:

Code:

         FileAmount = argv[2] - '0';

argv[2] is a char * (that is, a text string), not a single char.

You probably want to use strtol() to convert argv[2] to an integer value (it does not at all have to be a hex value - you need a short integer).

--
Mats

Originally Posted by Pharrox

As for only writing three bytes instead of four, the fourth will always be null so it doesn't really need to be specified by the program.

Yes, but you NEED to store the null byte, otherwise the code reading the information will read some other byte when it reads the 4 bytes in to check the value.

--
Mats

You need to pass the ADDRESS of your integer (which should be of the type short or unsigned short), and then cast that to char *.

--
Mats

Just another take on the problem: it seems to me that you have a null terminated string that is the textual input of the number of files. You want to write this to the output file in hexadecimal notation.

This suggests a two step process: first, convert the null terminated string to an integer, and then write that integer to file file output stream formatted in hexadecimal, e.g.,

Code:

const char num_files_as_text[] = "3";
std::stringstream ss(num_files_as_text);
int num_files;
ss >> num_files;
output << "0x" << std::setfill('0') << std::setw(4)
    << std::hex << std::noshowbase << num_files;

where output is the ofstream in your own example, and you need to #include <iomanip> and <sstream>.

Originally Posted by Pharrox

Okay, one more quick question.

How can I write a stream of bytes in reverse? There are four bytes I need to write but they always output as 4321 instead of 1234.

You either have to do lots of seekp() or reverse it before you write it. The latter is huge number of times faster than the former.

--
Mats

Actually I'm trying to write another integer (the size of the file). If I typecast that the same way as my previous problem it will write in reverse. I tried putting it into another character array, reversing that, and writing to the file, but all the data got changed. Since it's actually writing an integer, how would I reverse it before writing?

EDIT: I just tested it again and it seems like it messes up the data on the first pass but the rest are fine. I think I may just have to change the order in which it does some things.