这不是一个字节一个字节的比较：为什么

Question

I would like to take two files, compare them byte-by-byte, and test it's performance,

So far, this is what my code looks like:

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

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

    printf("Enter name of first file :") ;
    gets(fname1);

    printf("Enter name of second file:");
    gets(fname2);

    clock();    

    fp1 = fopen( fname1,  "r" );
    fp2 = fopen( fname2,  "r" ) ;

    if ( fp1 == NULL )
    {
        printf("Cannot open %s for reading\n", fname1 );
        exit(1);
    }
    else if (fp2 == NULL)
    {
        printf("Cannot open %s for reading\n", fname2 );
        exit(1);
    }
    else
    {
        ch1  =  getc( fp1 ) ;
        ch2  =  getc( fp2 ) ;

        while( (ch1!=EOF) && (ch2!=EOF) && (ch1 == ch2))
        {
            ch1 = getc(fp1);
            ch2 = getc(fp2);
        }

        if (ch1 == ch2)
            printf("Files are identical\n");
        else if (ch1 != ch2)
            printf("Files are Not identical\n");

        fclose ( fp1 );
        fclose ( fp2 );
    }

    printf("That took %d seconds.\n", clock() / CLOCKS_PER_SEC);

    return 0;
}

I was told: "==" is NOT a byte-by-byte comparison, how can I implement this so that I can XOR bitwise operations?

Also, is there a way to check how much duplication is in a single file itself?

Thanks for your help in advance!

Answer 1

In example 2, you aren't checking for end of file. That's why it never stops.

You are comparing byte by byte. I think both versions will be fine once you fix the second version.

Another couple things you might consider:

• If this may run on a Windows machine, use "rb" instead of "r" so that Windows won't convert line ending characters.
• You might want to add a ferror() test as well as the EOF. You won't usually need it, but I normally include it just in case.