topic Re: Rename a file in C++ on Unix platform in Operating System - Linux

Rename a file in C++ on Unix platform

Soumya Krishnan — Tue, 10 Jun 2008 15:08:00 GMT

Hi All,

I have a c++ code to rename a pdf file using io.h.While trying to run the same code in unix platform it is giving error message.Is there any way to rename in c++ which is compatible to unix.Or How could i rectify this problem.Please give a suggestion
c++ code
rename(tmpfn[0], filename)

Thanks in Advance
Soumya...

Re: Rename a file in C++ on Unix platform

James R. Ferguson — Tue, 10 Jun 2008 15:26:36 GMT

Hi:

Well, 'rename()' is the Unix system call to change the name of a file (of course).

You need to specify what "error (message)" you are getting. You *should* be examining any 'errno' returned when the return status of the 'rename' isn't zero. That should tell you the reason for your failure.

I would also re-read the manapges:

http://docs.hp.com/en/B3921-60631/rename.2.html

For instance, are your source and target names in the same filesystem. If not, you can't 'rename()'.

Regards!

...JRF...

Re: Rename a file in C++ on Unix platform

Soumya Krishnan — Wed, 11 Jun 2008 06:22:08 GMT

Hii James,

Thanks a lot for your suggestion .
The error number i got is errno=18
[EXDEV]
The paths named by source and target are on different logical devices (file systems).
What shall i do for this.
I am trying to rename a file from the folder
/var/tmp/xyz.pdf to ./Result/abc.pdf
means from a system temporary folder to application folder

Re: Rename a file in C++ on Unix platform

Steven Schweda — Wed, 11 Jun 2008 06:34:06 GMT

> What shall i do for this.

What would you like to do? Many things are
possible. For example:

1) When you get EXDEV, quit.

2) When you get EXDEV, copy the file, and
then, if that works, delete the original
file.

3) Don't create the temporary file in
/var/tmp. Instead, create it in the
destination directory (with some funny name),
and when it's ready, rename it to the
desired name.

Some programs (Info-ZIP Zip, for example)
will try to do 3, but if the rename fails
for some reason, it'll try to do the job with
a copy. (And if that fails, it'll complain.)

Re: Rename a file in C++ on Unix platform

Dennis Handly — Wed, 11 Jun 2008 07:50:18 GMT

>I am trying to rename a file from /var/tmp/xyz.pdf to ./Result/abc.pdf

As Steven says, you can't do that directly if not on the same filesystem.

If you are real lazy, you can use system(3) to invoke mv(1):
system("mv /var/tmp/xyz.pdf ./Result/abc.pdf");

Of course if the two files are variables, you would have to use strcpy and strcat to form the string. Or use:
snprintf(buf, sizeof(buf), "mv %s %s", from_file, to_file);

Re: Rename a file in C++ on Unix platform

Torsten. — Wed, 11 Jun 2008 10:42:14 GMT

You want to "rename"

/var/tmp/xyz.pdf to ./Result/abc.pdf

You need to copy the source to the target and delete the source - well known as move.
If you give the target file another name while creating, you have what you want.

Re: Rename a file in C++ on Unix platform

James R. Ferguson — Wed, 11 Jun 2008 10:56:02 GMT

Hi:

Now you see the immediate value of interrogating the 'errno' on failure of a system call, as I first suggested. Interestingly, too, your failure (EXDEV) was the one I suspected as I noted :-)

Using the shell 'mv' command does a *copy* in lieu of a 'rename' whenever a file resides in different filesystems. You could take this middle-ground in your code:

If the source and destination names aren't at the same root directory, you could assume that different filesystem may be involved and call 'system()' with 'mv', otherwise you could perform the 'rename()' directly.

Regards!

...JRF...

Re: Rename a file in C++ on Unix platform

Soumya Krishnan — Wed, 11 Jun 2008 12:00:21 GMT

Thanks all
system move command is working fine in unix..Its is not working in windows.But i need a way that renames the file both in unix and windows.

Re: Rename a file in C++ on Unix platform

James R. Ferguson — Wed, 11 Jun 2008 12:07:19 GMT

Hi (again):

> But i need a way that renames the file both in unix and windows

use Perl;

Write a simple Perl script using the File::Copy module. This implements things in a platform independent fashion.

Regards!

...JRF...

Re: Rename a file in C++ on Unix platform

Torsten. — Wed, 11 Jun 2008 12:09:45 GMT

If this is C code, you can do your own move.
Open the file, read it and write the contents to a new file. Close both and delete the source. Don't forget some error checking/exception handling.

Re: Rename a file in C++ on Unix platform

Steven Schweda — Wed, 11 Jun 2008 15:19:57 GMT

> But i need a way that renames the file both
> in unix and windows.

I thought that I explained how to do it, as
have others. I even explained how to avoid
the problem by writing your temporary file to
the right place, instead of to "/var/tmp".
Do you need someone to write the code for
you, or what? What's not clear yet?

Re: Rename a file in C++ on Unix platform

Soumya Krishnan — Wed, 11 Jun 2008 15:21:25 GMT

Hii...

Thanks alot........
It is working fine now.I have used Preprocessor directives for the compatiblity problem .
#ifdef UNIX

system("mv /var/tmp/xyz.pdf ./Result/abc.pdf");

#else
if(rename(tmpfn[0], filename))
{
map_msg_err("Can't rename temp-PDF file '%s' to '%s'\n", tmpfn[0], filename);
mexit(EXIT_PDFRENAME);
}
#endif

Once again thanking u all for ur valubale suggestions...:-)

Re: Rename a file in C++ on Unix platform

Torsten. — Wed, 11 Jun 2008 15:28:28 GMT

Even if this works under some circumstances, I really doubt if "rename" will always "move" your file ... but it's your code ...

Re: Rename a file in C++ on Unix platform

James R. Ferguson — Wed, 11 Jun 2008 15:31:22 GMT

Hi:

As a new Forum member, welcome! If you are happy with the suggestions you have received, please read:

http://forums11.itrc.hp.com/service/forums/helptips.do?#28

Regards!

...JRF...

Re: Rename a file in C++ on Unix platform

Steven Schweda — Wed, 11 Jun 2008 15:35:22 GMT

> [...] ... but it's your code ...

Yeah. Sometimes it'd be nice to know more
about the people who post these questions, so
you'd know what not to buy.

Re: Rename a file in C++ on Unix platform

Torsten. — Wed, 11 Jun 2008 15:38:46 GMT

LOL

Steven, we have the same point of view.