Thread: Reading a file in hexidecimal

Im haveing trouble reading a file in hexidecimal. Lets say I have a file called "something.txt" which goes as follows:

Hello
1234567890
©§¥
!@#$%^&*()

My program display lines 1,2, and 4 correctly but I get some strange errors on line 3. This is my code:

Code:

#include <iostream.h>
#include <fstream.h>
#include <stdio.h>

int main()
{
	char charVal[1] = "";
	char hexVal[3]  = "";
	char charSingle = ' ';
	int  intVal     =  0;
	ifstream file("something.txt", ios::binary);
	while(!file.eof())
	{
		file.read(charVal, 1);
		charSingle = charVal[0];
		intVal = (unsigned int)charSingle;
		sprintf(hexVal,"%X", intVal);
		cout << hexVal << " ";
	}
	return 0;
}

On the third line my program outputs: "FFFFFFA9 FFFFFFA7 FFFFFFA5"

If I replace the last line in my code to "cout << intVal << " ";" Then it outputs: "-87 -89 - 91". Why am I getting negatives? If I put this code:

Code:

intVal = (unsigned int)'©';
sprintf(hexVal,"%X", intVal);
cout << hexVal << " ";

outside of the while loop it displays "FFFFFA9". However if I were to replace it with this code:

Code:

intVal = 169; // 169 is the decimal value for ©
sprintf(hexVal,"%X", intVal);
cout << hexVal << " ";

it displays "A9" instead of "FFFFFFA9" which is what the -87 value was doing.

I looks like when you convert your signed char to an unsigned int, It's not "throwing-away" the sign bit. Which makes sense.

This seems to work:

Code:

#include <iostream.h>
#include <fstream.h>
#include <stdio.h>

int main()
{
	unsigned char charVal[1] = "";
	char hexVal[3]  = "";
	unsigned char charSingle = ' ';
//	int  intVal     =  0;
	ifstream file("c:\\C++ Programs\\something.txt", ios::binary);
	while(!file.eof())
	{
		file.read(charVal, 1);
		charSingle = charVal[0];
//		intVal = (unsigned int)charSingle;
		sprintf(hexVal, "%X", charSingle);
		cout << hexVal << " ";
	}
	return 0;
}