Needed APIs: For copying file and finding Disk Usage

Dear all,
I am programming in Linux , wherein I need to know a couple of
things.

1) Does an API exist that can copy file onto another file ( an API
equivalent of 'cp') ?


2) Is there an API that tells me the disk usage ( equivalent for
cmdline
'du' ) ?


Any pointers would be greatly appreciated.


Thanks n

re: Needed APIs: For copying file and finding Disk Usage

Sankar wrote:Please try posting to comp.os.linux.* comp.unix.programmer etc.

Also see the link below to try to find what you want:
<http://www.gnu.org/software/libc/manual/html_node/index.html>

re: Needed APIs: For copying file and finding Disk Usage

On Mon, 04 Dec 2006 18:01:09 -0800, Sankar wrote:
The following isn't guaranteed, I believe, by any ISO C standard to work,
per se (though it's difficult to discern exactly what you're asking), but
within the domain of Unix platforms/implementations (including Linux) the
unspecified parts are specified and implemented so:

#include <stdio.h>
/* FILE fopen(3) fread(3) fwrite(3) feof(3) fflush(3) */

#include <stdlib.h>
/* EXIT_FAILURE exit(3) */

int main(void) {

FILE *src, *dst;
unsigned char buf[1024];
size_t n;

if (0 == (src = fopen("/path/to/source/file", "r")))
perror("fopen"), exit(EXIT_FAILURE);

if (0 == (dst = fopen("/path/to/sink/file", "w")))
perror("fopen"), exit(EXIT_FAILURE);

while (0 < (n = fread(buf, 1, sizeof buf, src))) {
if (n != fwrite(buf, 1, n, dst))
perror("fwrite"), exit(EXIT_FAILURE);
}

if (!feof(src))
perror("fread"), exit(EXIT_FAILURE);

if (0 != fflush(dst))
perror("fflush"), exit(EXIT_FAILURE);

return 0;

}

You need to ask in a Linux-specific forum.

- Bill

re: Needed APIs: For copying file and finding Disk Usage

Sankar wrote:.... snip ...#include <stdio.h>
int main(void) {
int ch;
while (EOF != (ch = getchar())) putchar(ch);
return 0;
}

copies stdin to stdout.
No. Standard C knows nothing about disks or the usage thereof.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

re: Needed APIs: For copying file and finding Disk Usage

William Ahern <william@25thandClement.comwrites:Why 1024? It would probably make more sense to use BUFSIZ.
This is an awkward use of the comma operator, IMHO. I'd write:

if ((src = fopen("/path/to/source/file", "r")) == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}

Note that the standard doesn't guarantee that fopen() sets errno.
Assuming that "cp" is an OS command that copies files (yeah, I know it
is, but this is comp.lang.c), it's likely to do a number of
system-specific things to optimize performance. If you don't mind a
Linux- or Unix-specific solution, you might consider invoking the "cp"
command itself via system(). <OT>The cp command does a number of
things that you can't do in portable C, as you can see by reading the
man page.</OT>

--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

re: Needed APIs: For copying file and finding Disk Usage

Sankar wrote:If the operating system is relevant then it's probably not a question
that can be answered within standard C. In particular system calls or
APIs such that you're asking for are not defined by C.
Not exactly, but you can write this one in standard C:

int cp(const char *source, const char *dest)
{
FILE *ifp = fopen(source, "rb");
FILE *ofp = fopen(dest, "wb");
int ch;
if(!ifp || !ofp) return -1;
while((ch = getc(ifp)) != EOF) putc(ch, ofp);
if(ferror(ifp) || ferror(ofp)) return -1;
if(fclose(ifp) || fclose(ofp)) return -1;
return 0;
}
No - this cannot be done in standard C. There are two choices: one is to
find a system-specific function you can call (OT: man statfs). The other
is to use the 'system' function to run your 'du' program through the
command line. If you redirect its output to a file you can then read
that file and parse it.

--
Simon.

re: Needed APIs: For copying file and finding Disk Usage

Sankar wrote:Sort of. There is a standard C function that will permit you to pass a
string argument to the "command processor to be executed in a manner
which the implementation shall document". This means that you /could/
system("cp fromfile tofile");
and "copy file onto another file" in a manner exactly the same as the
Unix cp(1) command.
Similarly, the system() function can invoke the du(1) command, but as
system() doesn't return the output of the command, you'll have to do
some trickery.
system("du >some.file");
followed by
FILE *diskusage = fopen("some.file", "r");
(with the appropriate error checking everywhere, of course)
This will tell you the disk usage /exactly/ as du(1) would.

HTH
--
Lew

re: Needed APIs: For copying file and finding Disk Usage

Simon Biber <news@ralmin.ccwrites:[...]And if your system has the "du" command, it probably has a
system-specific function that lets a C program read the output of a
command without writing it to a temporary file. Which is why this is
a question for comp.unix.programmer, where the function in question is
topical.

--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

re: Needed APIs: For copying file and finding Disk Usage

"Keith Thompson" <kst-u@mib.orgwrote in message
news:lnu00avqe9.fsf@nuthaus.mib.org...It's awkward, yes, but still legal. It's also the only use I've found
for the comma operator other than incrementing multiple variables in a
"for" construct.

The problem is that many folks will not notice it's a comma (expecting a
semicolon), or will think it's a typo. That leads to maintenance
problems. It's also not done widely enough to be considered idiomatic,
so I wouldn't use it in an example for a newbie, but I use it in my own
code now and then.

For instance, I once had to change several hundred "close(fd);"
statements to also do "fd=-1;". Since most, but not all of them, were
bare statements underneath an if, the simplest way was a simple
find-and-replace with "close(fd), fd=-1;" Not clean, and I'm not proud
of it, but it worked perfectly and saved me a lot of time.

You'll also see it in macros now and then, as a way to avoid needing the
"do {...} while (0)" trick. It's debatable which construction is worse,
but as long as it's confined to macros most people won't comment.

S

--
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking


--
Posted via a free Usenet account from http://www.teranews.com

re: Needed APIs: For copying file and finding Disk Usage

"Stephen Sprunk" <stephen@sprunk.orgwrites:Yes, I agree that it's perfectly legal.
Well, I never write bare statements under an if (I always use braces,
even for a single statement), but like all style questions that's
largely a matter of taste.
The "do {...} while (0)" trick is IMHO ugly, but it's a common idiom
and there's often no other way to achieve the same goal. Using comma
operators to avoid it seems reasonable to me.

--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

re: Needed APIs: For copying file and finding Disk Usage

"Stephen Sprunk" <stephen@sprunk.orgwrites:
C has a construct called "functions" that can be usefully applied
to reduce duplication. For example:

void
my_close (int *fd)
{
close (*fd);
*fd = 1;
}

Then, later, when you want to check whether the fd is -1 before
closing it, you only have to change one place.
--
"Welcome to the wonderful world of undefined behavior, where the demons
are nasal and the DeathStation users are nervous." --Daniel Fox

re: Needed APIs: For copying file and finding Disk Usage

Stephen Sprunk wrote:I always use a compound statement in my if statements.
That's most of the reason why
I always use a compound statement with an if, or an else, or a loop.
I use comma style macros whenever I can.

#define SWAP(A, B, T) \
((void)(*(T) = *(A), *(A) = *(B), *(B) = *(T)))

If the macro needs to contain statements
which are not expression statements, then I can't.

--
pete

re: Needed APIs: For copying file and finding Disk Usage

On Tue, 05 Dec 2006 05:54:38 +0000, Keith Thompson wrote:
<snip>Yes. However, I didn't have my copy of the standard at-hand, and figured
I'd rather take the lashing for not using it, rather than to use it but
document it's source incorrectly ;)
I often use the comma operator like so

if (some_arg == 0)
return (errno = EINVAL), -1;

because I'm trying to express that I'm returning a particular state, not
simply doing a series of actions and then returning a value.

I carried it over to the example, but I agree that the example code is a
awkward. Neither the former (perror()) nor latter (exit()) action
in the expression strictly follows the pattern I use when employing the
comma operator in that situation. I suppose I was simply trying to be
terse