Reading two files one byte at a time

Question

I am currently trying to write a program that reads two files one byte at a time (yes I am aware of the heavy I/O overhead), but I am having trouble incrementing the FILE pointer. I would like to program to compare both files byte-by-byte, and getc would not be a viable option for it would only work for chars because chars are one byte. However, I am reading from two text files and the text file could include numbers such as ints, doubles, etc. Therefore, in such scenario I would like to grab that byte from part of the int/double and compare it to the other file (a sequential byte-by-byte comparison).

Here is what I have so far:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include <time.h>

#define BUFFER_SIZE 1

unsigned char buffer1[BUFFER_SIZE];
unsigned char buffer2[BUFFER_SIZE];

int main()
{
    FILE *fp1, *fp2;
    int ch1, ch2;
    clock_t elapsed;
    char fname1[40], fname2[40];

    printf("Enter name of first file :");
    fgets(fname1, 40, stdin);
    while ( fname1[strlen(fname1) - 1] == '\n')
    {
        fname1[strlen(fname1) -1] = '\0';
    }

    printf("Enter name of second file:");
    fgets(fname2, 40, stdin);
    while ( fname2[strlen(fname2) - 1] == '\n')
    {
        fname2[strlen(fname2) -1] = '\0';
    }

    fp1 = fopen(fname1, "r");
    if ( fp1 == NULL )
    {
        printf("Cannot open %s for reading\n", fname1 );
        exit(1);
    }

    fp2 = fopen( fname2,  "r");
    if (fp2 == NULL)
    {
        printf("Cannot open %s for reading\n", fname2);
        exit(1);
    }

    elapsed = clock(); // get starting time

    /* Read in 256 8-bit numbers into the buffer */
    size_t bytes_read1 = 0;
    size_t bytes_read2 = 0;

    bytes_read1 = fread(buffer1, sizeof(unsigned char), BUFFER_SIZE, fp1); 
    bytes_read2 = fread(buffer2, sizeof(unsigned char), BUFFER_SIZE, fp2); 

    printf("%c + in buffer 1\n", *buffer1);
    printf("%c + in buffer 2\n", *buffer2);

    fclose ( fp1 ); // close files
    fclose ( fp2 );

    elapsed = clock() - elapsed; // elapsed time
    printf("That took %.4f seconds.\n", (float)elapsed/CLOCKS_PER_SEC);
    return 0;
}

I am assuming buffer1 and buffer2 are the content of the one byte being read? Would I have to convert them to a number to compare them? I was thinking I could do the comparison as follows

(buffer1 ^ buffer2) == 0 

Then that would mean they are equal based on the XOR bitwise operation

Thanks for your help in advance

Answer 1

I have enjoyed the banter in the comments. Maybe time for an example.

Note: In a text file, an alpha character such as "a" will be interpreted as 'a' (97, or 0x61). A numeric character, such as "2" will be interpreted the same way, as '2' (50, or 0x32). A file is just a collection of alphanumeric, punctuation, or white-space characters that using fgetc(), can be looked at one character at a time.

Contrary to your assertion that fgetc() will not work for a byte by byte comparison, Here is a simple example that shows it does. Showing code using fgetc() with inputs and results for same contents files, and different contents files:

#include <ansi_c.h>//this is a collector of the ansi C headers.  Pick the one in your
                   //environment that work for you.
#include <limits.h>

#define FILE1 "C:\\dev\\play\\file1.txt"
#define FILE2 "C:\\dev\\play\\file2.txt"

BOOL CompareFileByteByByte(char *file1, char *file2);

int main(void)
{

    if(CompareFileByteByByte(FILE1, FILE2))
    {
        printf("Files are equal\n");
    }
    else
    {
        printf("Files are NOT equal\n");
    }


    return 0;
}

BOOL CompareFileByteByByte(char *file1, char *file2)
{
    FILE *fp1=0, *fp2=0;
    BOOL results = 0;

    int c1 = 0, c2 = 0;//note, even though getc reads one char from file, 
                       //it uses int as return to accomodate -1 (EOF)

    fp1 = fopen(FILE1, "r");
    fp2 = fopen(FILE2, "r");


    c1 = fgetc(fp1);
    c2 = fgetc(fp2);

    results = (c1 == c2);

    while((c1!=EOF) && (c2 != EOF) && results)
    {
        c1 = fgetc(fp1);
        c2 = fgetc(fp2);
        results = (c1 == c2);
    }

    return results; 
}

Given FILE1 FILE2: (both same)

Oringinal text...
...more text 123456
...more text 2.3456
...more text 3e12

Results: Files are equal

Given FILE1

Oringinal text...
...more text 123456
...more text 2.3456
...more text 3e12

And FILE2

Oringinal text...
...more text 123456
...more text 2.3456
...more text 4e12

Results: Files are NOT equal