How do I copy content of one file to another

Question

This is my file copying code:

void main()
{
    char c;
    FILE *fptr1, *fptr2;

    fptr1=fopen("abc.docx","r");
    fptr2=fopen("paste_here.docx","w");

    c=fgetc(fptr1);
    while (c!=EOF)
    {
        putc(c,fptr2);
        c=fgetc(fptr1);
    }
    fclose(fptr1);
    fclose(fptr2);
}

I expected the contents to get copied but whenever I try to open paste_here.docx file after running this, it says that the file can't be opened as there are problems with the contents.

Is the output file the correct size? You should have defined `char c;` as `int c;` and a data value of `0xFF` may have caused premature ending of the loop. — Weather Vane, Jul 08 '19 at 06:05
Use `fread`and `fwrite` instead, reading/writing char by char is very inefficient. Youz shoulkd also indent your code (just like the samples in your C text book) — Jabberwocky, Jul 08 '19 at 06:05
It doesn't say if you are using Miscosoft compiler, but if you are, you must specify the file r/w mode when copying a file like this, binary mode `"rb"` and `"wb"` to prevent data that looks like (but is not) a line-end character being converted. — Weather Vane, Jul 08 '19 at 06:09
See also [`while ((c = getc(fp)) != EOF)` loop won't stop executing](https://stackoverflow.com/questions/13694394/) — you can also run foul of premature EOF if the byte 0xFF is present in the file being copied unless you use the `b` flag. — Jonathan Leffler, Jul 08 '19 at 06:25
@Jabberwocky, a character oriented read relies on an underlying read-buffer and is quite efficient. For example `fgetc()` actually reads from a `BUFSIZ` buffer (previously `_IO_BUFSIZ` in gcc source) which is 8192 bytes on Linux, and 512 bytes on Windows. So a char-by-char read is no less efficient than a read with `fgets` using an 8192 byte buffer. (see: `_IO_BUFSIZ` changed to `BUFSIZ` [glibc commit 9964a14579e5eef9](https://sourceware.org/git/?p=glibc.git;a=commit;h=9964a14579e5eef925aaa82facc4980f627802fe)) — David C. Rankin, Jul 08 '19 at 07:01
@DavidC.Rankin but even with a buffer (512 on Windows is tiny BTW) there is an overhead, but actually I didn't mesure. — Jabberwocky, Jul 08 '19 at 07:35
I agree, for a zippier copy, a `memmap` or `sendfile` (Linux) can easily best the large block copy in user-space. `sendfile` even manages to do most of the copy in kernel-space. — David C. Rankin, Jul 08 '19 at 07:41

score 0 · Answer 1 · answered Jul 08 '19 at 07:25

0

Above code works well with GCC compiler. however, this should not be dependent on the compiler.

Here are the two types of file data

1 - text file easy to read and write.

2 - binary files having complex and encrypted information.

Suggestion :

For a text file, we would suggest you use fprintf() and fscanf() function for reading and writing operation.

For a binary file, we would suggest you use fread() and fwrite() funtion for reading and writing operation.

answered Jul 08 '19 at 07:25

dragon

132
6

2

The fact that "binary files having complex and encrypted information" is not relevant to the question. The OP just wants to copy a file regardless of it it's a binary or a text or whatever file. – Jabberwocky Jul 08 '19 at 07:37
I'm very new to all this so I don't really understand what a binary file is. My initial code worked only on .txt files. But when I opened a .docx file in rb and wb mode, the same code worked. THANKS a lot. It would be really great if you could please explain to me why this is happening. Also can I do the same for .xls files? – Kashvi Gandhi Jul 08 '19 at 17:48
1

@KashviGandhi refer to below link for better understanding between 'r' and rb' https://stackoverflow.com/questions/2174889/whats-the-differences-between-r-and-rb-in-fopen for 'w' and 'wb' https://stackoverflow.com/questions/43777913/the-difference-in-file-access-mode-w-and-wb hope you will the idea from here. if you think the above post works for you, pls upvote this answer. – dragon Feb 21 '20 at 06:44

How do I copy content of one file to another

1 Answers1