shutil.copy in c

[yinglcs]

Hi,

Is there a c library which does shutil.copy2() in python? Basically
copy a file from 1 directory to another?

import shutil
import os

shutil.copy2(r"C:\test\test",r"C:\test1\test")

Thank you.

 

[Pietro Cerutti]

Hi,

Is there a c library which does shutil.copy2() in python? Basically
copy a file from 1 directory to another?

Standard C doesn't know anything about files or directories.
What you need is an OS-specific library function / system call, better
discussed in a newsgroup related to your system.

 

[Walter Roberson]

Is there a c library which does shutil.copy2() in python? Basically
copy a file from 1 directory to another?

Not in standard C, no. There is no file copy utility in the
C standard.

There will likely be the usual responses about opening the file,
reading it a char at a time and writing the chars to an output
file. However, "files" may have attributes other than just
their contents (especially if the filename is a device!),
and there is no way in standard C to discover or duplicate
those attributes. I would suspect that python's shutil.copy2()
*does* have a way of detecting and dealing with those attributes.

In Windows (based upon the filenames you gave), the sort
of attributes you might want copied could include the
alternate data streams, and the security rights.

 

[Keith Thompson]

Standard C doesn't know anything about files or directories.
What you need is an OS-specific library function / system call, better
discussed in a newsgroup related to your system.

It doesn't know about directories, but it does know a thing or two
about files.

 

[Jens Thoms Toerring]

Standard C doesn't know anything about files or directories.

Nitpick alarm: the C standard luckily at least admits to the
existence of files, otherwise functions like fopen(), fread()
etc. would rather likely not exist (or do something else than
what they are required to do;-)
Regards, Jens

 

[Richard Bos]

Is there a c library which does shutil.copy2() in python? Basically
copy a file from 1 directory to another?

import shutil
import os

shutil.copy2(r"C:\test\test",r"C:\test1\test")

I cannot fathom the need for a specific function to copy from one
directory to another, given both complete file names. Surely if you have
filename1 and filename2, that should allow you to do a copy from the one
to the other regardless of whether either of them is in any directory or
whether the system has directories at all?
In any case, given two file names, the procedure in C is simple.
fopen(filename1, "rb"), fopen(filename2, "wb"), fread() from file 1 and
fwrite() to file 2 until you run out of data, fclose() both files.
That's it. No need to fret about directories.

Richard

 

[Keith Thompson]

I cannot fathom the need for a specific function to copy from one
directory to another, given both complete file names. Surely if you have
filename1 and filename2, that should allow you to do a copy from the one
to the other regardless of whether either of them is in any directory or
whether the system has directories at all?
In any case, given two file names, the procedure in C is simple.
fopen(filename1, "rb"), fopen(filename2, "wb"), fread() from file 1 and
fwrite() to file 2 until you run out of data, fclose() both files.
That's it. No need to fret about directories.

If you need your program to be as portable as possible, that's the way
to do it. But very often there can be requirements other than
portability. If I had a need to copy a file in a C program intended
to run under a Unix-like system, I'd invoke the "cp" command; this is
likely (but not certain) to be faster than a pure C solution, and it
gives me more options regarding *how* to copy the file (most of which
are outside the scope of C). Under Windows (implied by the file names
used by the OP), I suppose I'd use "copy" for the same reasons.

I'm not very familiar with Python, but I presume that 'shutil.copy2'
is an abstraction that invokes "cp", or "copy", or whatever. With
some effort, you can build the same kind of abstraction in C -- and
I'm sure it's already been done.

 

[Roland Pibinger]

In any case, given two file names, the procedure in C is simple.
fopen(filename1, "rb"), fopen(filename2, "wb"), fread() from file 1 and
fwrite() to file 2 until you run out of data, fclose() both files.
That's it.

A production quality copy function in C is not trivial. The code you
can find on the internet is mostly defective. A production quality
copy function at least needs:
- an explicit policy wrt overwriting an existing file
- preparation for the worse cases, ie. return values of read, write,
and close functions and/or stream state must be checked
- preparation for the worst case, the crash during copying

The last requirement implies that the file is first written to a
temporary file (in the same directory as the destination file) and
renamed later after all copying is reliably finished. A production
quality copy function would probably use the Posix I/O functions
instead of stdio because they provide some essential features not
present in stdio, e.g. you can open a file with O_CREAT | O_EXCL or
flush data to disk with fsync (_commit on Windows).

 

[Richard Bos]

If you need your program to be as portable as possible, that's the way
to do it. But very often there can be requirements other than
portability.

True enough, though I doubt it's going to make much of a difference in
speed at least unless you copy a lot of files.

If I had a need to copy a file in a C program intended
to run under a Unix-like system, I'd invoke the "cp" command; this is
likely (but not certain) to be faster than a pure C solution, and it
gives me more options regarding *how* to copy the file (most of which
are outside the scope of C). Under Windows (implied by the file names
used by the OP), I suppose I'd use "copy" for the same reasons.

I would hesitate to call the actual program, presumably using system()
or something similar but system-specific. Most APIs should have
functions to do all that for you.

Richard

 

[Keith Thompson]

I would hesitate to call the actual program, presumably using system()
or something similar but system-specific. Most APIs should have
functions to do all that for you.

Really? The API I'm most familiar with (Unix) doesn't provide a
function to copy an entire file, as far as I know, other than invoking
the 'cp' program.

 

[Richard Bos]

Really? The API I'm most familiar with (Unix) doesn't provide a
function to copy an entire file, as far as I know, other than invoking
the 'cp' program.

It doesn't? Odd. I can't imagine where I got that impression, then.
Except, of course, that MS Windows does have one.

Richard