Needed APIs: For copying file and finding Disk Usage

[Sankar]

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

[santosh]

Sankar wrote:

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.

Please try posting to comp.os.linux.* comp.unix.progr ammer etc.

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

[William Ahern]

On Mon, 04 Dec 2006 18:01:09 -0800, Sankar wrote:

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') ?

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_FAILU RE);

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

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

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

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

return 0;

}

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

You need to ask in a Linux-specific forum.

- Bill

[CBFalconer]

Sankar wrote:

>

.... snip ...

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

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

copies stdin to stdout.

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

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>

[Keith Thompson]

William Ahern <wi*****@25than dClement.comwri tes:

On Mon, 04 Dec 2006 18:01:09 -0800, Sankar wrote:

>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') ?

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];

Why 1024? It would probably make more sense to use BUFSIZ.

size_t n;

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

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_FAILU RE);
}

Note that the standard doesn't guarantee that fopen() sets errno.

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

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

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

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

return 0;

}

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_Keit h) ks***@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.

[Simon Biber]

Sankar wrote:

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

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.

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

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;
}

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

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.

[Lew Pitcher]

Sankar wrote:

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') ?

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.

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

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.fil e", "r");
(with the appropriate error checking everywhere, of course)
This will tell you the disk usage /exactly/ as du(1) would.

HTH
--
Lew

[Keith Thompson]

Simon Biber <ne**@ralmin.cc writes:

Sankar wrote:

[...]

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

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.

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.progr ammer, where the function in question is
topical.

--
Keith Thompson (The_Other_Keit h) ks***@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.

[Stephen Sprunk]

"Keith Thompson" <ks***@mib.orgw rote in message
news:ln******** ****@nuthaus.mi b.org...

William Ahern <wi*****@25than dClement.comwri tes:

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

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_FAILU RE);
}

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

[Keith Thompson]

"Stephen Sprunk" <st*****@sprunk .orgwrites:

"Keith Thompson" <ks***@mib.orgw rote in message
news:ln******** ****@nuthaus.mi b.org...

>William Ahern <wi*****@25than dClement.comwri tes:

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

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_FAILU RE);
}

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.

Yes, I agree that it's perfectly legal.

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.

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.

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.

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_Keit h) ks***@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.