#include <stdio.h>
#include <windows.h>

// procedure to get a files size and handles large files
long long GetFileSizeLocal(const TCHAR *fName)
{
    BOOL                        Ok;
    WIN32_FILE_ATTRIBUTE_DATA   fInfo;

    if (NULL == fName)
        return (long long) -1;

    Ok = GetFileAttributesEx(fName, GetFileExInfoStandard, (void*)&fInfo);
    if (!Ok)
        return (long long) -1;
    return (long long)fInfo.nFileSizeHigh * 0x100000000 + fInfo.nFileSizeLow;
}

int main()
{
    FILE *fptr1, *fptr2; // File Handles
    char filename1[100], filename2[100]; // File Names
    long long pos = 0;   // File Position
    long long rlen;  // Record Length to read and write
    long long sz1, sz2; // Size of files
    long long bufsize = (1024 * 1024); // 1 MB Buffer size
    char buf[bufsize]; // 1 Megabyte buffer
    long long lenread;  // bytes actually read
    long long lenwrite; // bytes actually written
    char check;  // read keyboard character

    printf("Enter the filename to open for reading \n");
    scanf("%s", filename1);
 
    // Open one file for reading
    fptr1 = fopen(filename1, "rb");
    if (fptr1 == NULL)
    {
        printf("Cannot open file %s \n", filename1);
//      Exit with first file error
        return 1;
    }

    sz1 = GetFileSizeLocal((TCHAR*)filename1);
    printf("File Size #1 is %lld.\n", sz1);

    fclose(fptr1);

    printf("Enter the filename to open for writing \n");
    scanf("%s", filename2);
 
//
    // See if File Exists and if so display warning
    fptr2 = fopen(filename2, "r");
    if (fptr2 != NULL)
    {
        fclose(fptr2);
        printf("File '%s' Already Exists. Do you want to Overwrite it?\n", filename2);
        check = getch();
        if (check == 110 || check == 78)  // "N" or "n"
//      Exit with second file error
        return 2;
    }

//
    // Open second file for writing
    fptr2 = fopen(filename2, "wb");
    if (fptr2 == NULL)
    {
        printf("Cannot open file %s \n", filename2);
//      Exit with second file error
        return 2;
    }

    sz2 = GetFileSizeLocal(filename2);
    fclose(fptr2);

//  Set up output line that we can backspace over
    printf("\nBytes Copied: %-12lld", 0);

//  Start of loop
    while (pos < sz1)
    {

    // Open first file for reading
    fptr1 = fopen(filename1, "rb");

    sz2 = GetFileSizeLocal(filename2);

    // Open second file for writing
    fptr2 = fopen(filename2, "ab");

    // get file #2 size which changes here
    sz2 = GetFileSizeLocal(filename2);

//  check if we need a full bufsize or less bytes to handle
    if ((sz1 - sz2) > bufsize)
        rlen = bufsize;
    else
        rlen = sz1 - sz2;

//  Set position of first file to read
    fseek(fptr1, pos, SEEK_SET);

//  Read bytes
    lenread = fread(buf, 1, rlen, fptr1);

//  Check for read errors and show error message and exit
    if (lenread != rlen)
    {
        printf("Read Error Occurred. Copy not completed!\n");
        fclose(fptr1);
        fclose(fptr2);
//      Exit with first file error
        return 1;
    }

//  Set position of second file to write
    fseek(fptr2, pos, SEEK_SET);

//  Write bytes
    lenwrite = fwrite(buf, 1, lenread, fptr2);

//  Check for write errors and show error message and exit
    if (lenread != lenwrite)
    {
        printf("Write Error Occurred. Copy not completed!\n");
        fclose(fptr1);
        fclose(fptr2);
//      Exit with second file error
        return 2;
    }

//  Close first file which is being read
    fclose(fptr1);

//  Close second file which is being written
    fclose(fptr2);

//  calculation the new file position where we are working
    pos = pos + bufsize;

//  Show progress on command line using same line and not scrolling
    printf("\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\bBytes Copied: %-12lld", pos);

//  End of loop here
    }

//  Show Finished Message
    printf("\nContents copied to %s", filename2);
 
//  Close First file used for reading
    fclose(fptr1);

//  Close Second file used for writing
    fclose(fptr2);

//  Exit with no error
    return 0;
}