Thread: Reading Hex Values From A File

That's because you end up printing what EOF is, which is typically -1

Your while loop should be
while ( (c = fgetc(in)) != EOF )

Further, when you call printf, you should cast c to unsigned int.
On your system at least, char is signed, which means it gets sign extended when c is in the range 0x80 to 0xFF

I suggest you post your latest code.

Perhaps you missed out a pair of ()

here is my code now...

Code:

    unsigned char c;
    while (!feof(in)) {
      c = fgetc(in);


      printf("%02x\n", c);
    }
    printf("\nEnd of file\n");

All I have done is change the char to unsigned.

Its printing this now... the ff at the end shouldn't be there.

1e
5e
c3
1e
40
ff

So in other words, you carried on using feof() incorrectly and ignored my corrected while loop.
FAQ > Why it's bad to use feof() to control a loop - Cprogramming.com

Also, c must be declared as an int, and only AFTER reading it should it be cast to an unsigned char for other purposes.

Thanks for the help Salem. I had a read of the FAQ and saw your suggestion shown on there. If you go back to my second from last post you will see I said that I said I tried to change the condition of the while loop just like you asked. For some reason though it seems to just endlessly print out "FF". I have posed the change here just encase I made a stupid mistake somewhere. I'm also now reading the characters into a int like you said and then casting to a char.

Code:

    unsigned char c;
    int a = 0;
    while ( ( (c = fgetc(in)) != EOF )) {
      a = fgetc(in);
      c = a;
     
      //int opcode = c & 0xc0;
      //opcode = opcode >> 6;


      //int operand = c & 0x3f;


      //printf("\n%d %d", opcode, operand);
      
      printf("%02x\n", c);
    }
    printf("\nEnd of file\n");

Like I said, c MUST be an int.

Code:

int c;
while ( ( (c = fgetc(in)) != EOF )) {
        printf("%02x\n", (unsigned)c);
}

fgetc() returns every possible value of char, and EOF.
In an 8-bit char, this means it has to return 257 possible values - hence it cannot itself return a char.

By making it a char, you implicitly cast what was the real EOF into some char, and at the same time make the != EOF test fail.
That's because (char)EOF != EOF