Not detecting EOF - c

Question

I hope this is not a turkey of a question. My conditional to detect EOF does not seem to work. The code continues through the EOF and processes within the statement. When I recreate the text, it appears appropriately, however the entire bmp with garbage code also prints out telling me the end of text flag never was encoded. I have placed a printf statement in the next else conditional, however it never enters that to print. I can not see what the problem is, if it is right in front of me, or something more ominous. Thanks as always!
/*******************************************************************************
* This code is to take a text document and using steganography techniques, hide
* the text within a bmp. It will take each character of the text, parse it into
* four 2 bit pieces and inject those bits into the two least significant bits
* of each pixel color (BGR) byte as well as the line padding.
******************************************************************************/
#include <stdio.h>
/*******************************************************************************
* getIntFromArray (borrowed from class notes). Takes unsigned character array
* and assembles/returns an int value using bit shifting with OR.
******************************************************************************/
int getIntFromArray(unsigned char bytes[])
{
int n =
bytes[0] |
bytes[1] << 8 |
bytes[2] << 16 |
bytes[3] << 24;
return n;
}
/*******************************************************************************
* bitWise. Take unsigned char pointer and character, parses the character
* using bitwise manipulation and injects 2 bits into the 2 least significant
* bits of each pixel color byte as well as padding.
******************************************************************************/
void bitWise(unsigned char* bytes, char character)
{
int i;
char tmpChar;
for(i = 0; i < 4; ++i)
{
tmpChar = character;
tmpChar &= 3;
bytes[i] &= 252;
bytes[i] |= tmpChar;
character = character >> 2;
}
}
int flag = 0;
int main(int argc, char **argv)
{
char *infilename = argv[1];
char *outfilename = argv[2];
unsigned char header[54];
FILE *in = fopen(infilename, "rb");/*Command line input.*/
FILE *out = fopen(outfilename, "wb");/*Command line input.*/
int pixelWidth;
int pixelHeight;
int i;
int j;
fread(header, 1, 54, in);/* read header into array */
pixelWidth = getIntFromArray(&header[18]);
pixelHeight = getIntFromArray(&header[22]);
fwrite(header, 1, sizeof(header), out);/* write header to output file */
for(i = 0; i < pixelHeight; ++i)/*Loop to read pixel data from bmp.*/
{
for(j = 0; j < pixelWidth; ++j)
{
unsigned char bytes[4];
unsigned char character = 0;
fread(&bytes, 1, 4, in);/*Reads sequentially pixel and padding bytes.*/
if(flag == 0)/*Breakout flag, initially set to 0.*/
{
character = getchar();/*Takes in characters from stdin.*/
if(character != EOF)/*Breakout if EOF.*/
{
bitWise(bytes, character);
}
else
{
bitWise(bytes, 0);/*Sets end of hidden text with 4 bytes LSB to 0.*/
flag = 1;
}
}
fwrite(&bytes, 1, 4, out);
}
}
fclose(in);
fclose(out);
return 0;
}

Answer 1

You are assigning signed int to an unsigned int. The result will be not what you expect it to be. It will be a value with all bits set to 1. (EOF has value -1 so it is signed).
Long story short it should be int. Simple int character would serves the purpose.
Also another thing getchar() returns int.
int getchar(void);
There are few other things to do :-
fread return value should be checked.
size_t fread(void * restrict ptr,size_t size, size_t nmemb,FILE * restrict stream);
The fread function returns the number of elements successfully
read, which may be less than nmemb if a read error or end-of-file
is encountered. If size or nmemb is zero, fread returns zero and
the contents of the array and the state of the stream
remain unchanged
Another thing is to check the return value of fopen(). In case of failure the return value would be NULL.

Answer 2

There are two serious but common problems here which lead me to believe you're not reading a reputable book, or you're having serious problems with it, as the reputable book would cover those problems in early chapters.
Perhaps we should look at some other options, since whatever you're using now clearly isn't working for you. You could've been reading your book all of this time you were struggling with trial and error, and your book should have guided you nicely past these common issues.
The bottom line is: you need to respect return values.
Don't try to convert return values before you check them. In unsigned char character; character = getchar(); you're converting from what the books and getchar manual says is an int to an unsigned char, before you try to check it against EOF. That conversion may result in loss of data. Do you wonder which data you've lost?
If you're struggling to understand K&R2E or a manual, you should write a question about that which you don't understand, rather than moving on, confused, to write code which relies upon guesswork. Any guesswork is dangerous in languages such as C.
You should also check the return value of fread, and I'd expect to see the size parameter passed 54 and the count parameter passed 1 in your case. That way, you can treat occasions when fread only reads fifty-three bytes (or fifty-two, or fifty-one) as though it's the end of input, rather than treating that unexpectedly short input as though it's the expected size. Like the getchar manual, you can find out all about fread from the fread manual.
Ohh, and nowadays I get a whole lot of "but the Youtube videos" responses. Youtube isn't a good substitute for a reputable book. Anybody can jump on there and "just wing it", and the video you watch will likely be equally flawed as your own guesses. A reputable book, on the other hand, has had thousands of hours put into planning, peer reviewing, testing (on students, since these books are usually written by professors who also have classes to teach) and refactoring (based on the testing, to better deal with "hiccups" that occur).
The choice should be obvious, and the proof is in the eating of the pudding. If you've tried the "youtube" or "try it and see" methods, they're not working for you; what you see before you now is the result of that. Try something else. Good luck!