how to get the updated result continuously by using popen command in c language?

[christyyim]

I'm now doing a project regarding the link traffic. In my project i try to use popen command to get the number of bytes i received in c programming and i successfully did so.
However here comes my problem, when i want to process the data I obtained, I found that this command keep giving me the same value without updating it. Here I post the code i roughly did in order to process the data.

#include <stdio.h>
#include <stdlib.h> /* required for atoi */

long int calculate();

main()
{

long int a[3];
long int b[5];
int i,j;

for (j=0; j<5; j++)
{
b[j]=0;
	for(i=0 ; i<3; i++)
	{
	a[i]=calculate();
	b[j]+= a[i];
	}
b[j]=b[j]/3;
printf("The number of bytes is: %d\n", b[j]);
}

}

long int calculate()
{
  FILE *fp;
  char line[130];			/* line of easa!from unix command*/
  int i;
 
  fp = popen("ifconfig eth0 |grep bytes|cut -c20-35", "r");		/* Issue the command.	*/

					/* Read a line	*/
  while ( fgets( line, sizeof line, fp))
  {
    printf("%s", line);		/* %s means string */
    i = atoi(line);
  }
  pclose(fp);
  
 return i;
}

Does anyone please help me figure out my problems or correct me if there is error on my code since i still a newbie to c language and linux world.

Thanks in advanced.

[gerard4143]

My system, Suse 11.0, doesn't have ifconfig..the information from "info ifconfig" says that ifconfig is obsolete and should not be used with kernels newer than 2.0. It also says that newer kernels should use ip...hope this helps

Welcome to the forums

[wje_lf]

I'm running Slackware 12.1, which is the current released version. There is no hint in the documentation included with Slackware that ifconfig is obsolete. I googled "ifconfig obsolete" and found few references to such an allegation, and they don't convince me. Furthermore, it works.

Furthermore, when I compile and run christyyim's program, that works too.

That program runs ifconfig 15 times fast, and pulls the total number of bytes received on eth0 from ifconfig's output each time. Each group of three result figures is averaged (arithmetically). Each of the five averages is sent to stdout. This works just fine.

My question, christyyim, is why you expect the number to change. ifconfig is run 15 times in very rapid succession, with no waiting between times. It's unlikely that a new packet will be completely received during this time. If I refresh a web page in my browser, say, and then run your program again, I get a slightly higher number, the same new one five times. This is what I would expect.

What seems to be the problem with your program? It seems to work just fine!

[christyyim]

Hi wje_lf,

actually if i run ifconfig command in the terminal, everytime it will give me different number of bytes that received, hence i think of averaging them to get a smoother graph. And this will be a start up point for me to get the wireless signal strength by using iwconfig command next. As you know, the wireless signal strength will vary much more than the number of bytes i received here since wireless is less stable than wired.

And from what u have observed is that ifconfig is run 15 times in very rapid succession, with no waiting between times. It's unlikely that a new packet will be completely received during this time.

Is it if i insert wait state before getting a new value I'll get different number of bytes? What i scare is once at the first time i execute the popen command, the number of bytes will be read at the FILE *fp and will not change even after the popen command execute again. And this is not what I wish.

and is it i can insert wait states by using sleep() command?

Thanks for your advices.

[wje_lf]

if i run ifconfig command in the terminal, everytime it will give me different number of bytes that received

Yes, but it's unlikely that you can type "ifconfig eth0" as fast (or even anywhere near as fast) as your program can run 15 of those. If you could type that fast, it would be likely that you would get the same number 15 times in a row. But you also have another problem:

hence i think of averaging them to get a smoother graph

I think you're under the impression that each time you run ifconfig, you're going to get the number of bytes received since the previous time you ran ifconfig. That's not true. You're going to get the number of bytes received since eth0 most recently came up.

Let's take an oversimplified example. Let's say eth0 is receiving three bytes per second, and that you're running ifconfig once every five seconds. That means you've received 15 new bytes each time you run ifconfig. But if you run ifconfig by hand at the prompt every five seconds, you're not going to get numbers like these:

15
15
15
15
15
15
15
15
15
15

Instead, you're going to get numbers like these:

246515
246530
246545
246560
246575
246590
246605
246620
246635
246650

So if you want to do this, you have to take each number you get and subtract from it the previous number. Of course, you have to not report the first number you get, because there's no previous number to subtract.

Is it if i insert wait state before getting a new value I'll get different number of bytes?

Yes.

What i scare is once at the first time i execute the popen command, the number of bytes will be read at the FILE *fp and will not change even after the popen command execute again.

That's exactly what's happening now. But it's not because of the way popen() works; it's because you haven't waited long enough for something new to happen.

is it i can insert wait states by using sleep() command?

Yes.

[gerard4143]

File: *manpages*, Node: ifconfig, Up: (dir)

IFCONFIG( Linux Programmer's Manual IFCONFIG(

NAME
ifconfig - configure a network interface

SYNOPSIS
ifconfig [interface]
ifconfig interface [aftype] options | address ...

DESCRIPTION
Ifconfig is used to configure the kernel-resident network interfaces.
It is used at boot time to set up interfaces as necessary. After that,
it is usually only needed when debugging or when system tuning is
needed.

WARNING: Ifconfig is obsolete on system with Linux kernel newer than
2.0. On this system you should use ip. See the ip manual page for
details

If no arguments are given, ifconfig displays the status of the cur-
rently active interfaces. If a single interface argument is given, it
displays the status of the given interface only; if a single -a argu-
ment is given, it displays the status of all interfaces, even those
that are down. Otherwise, it configures an interface.

Address Families
If the first argument after the interface name is recognized as the
name of a supported address family, that address family is used for
decoding and displaying all protocol addresses. Currently supported
address families include inet (TCP/IP, default), inet6 (IPv6), ax25
(AMPR Packet Radio), ddp (Appletalk Phase 2), ipx (Novell IPX) and
netrom (AMPR Packet radio).

[wje_lf]

This is quite interesting. What you're getting, of course, is the man page, infoized.

The one distributed with slackware 12.1, in its entirety:

IFCONFIG(8)                Linux Programmer's Manual               IFCONFIG(8)



NAME
       ifconfig - configure a network interface

SYNOPSIS
       ifconfig [-v] [-a] [-s] [interface]
       ifconfig [-v] interface [aftype] options | address ...

DESCRIPTION
       Ifconfig is used to configure the kernel-resident network interfaces.
       It is used at boot time to set up interfaces as necessary.  After that,
       it is usually only needed when debugging or when system tuning is
       needed.

       If no arguments are given, ifconfig displays the status of the cur-
       rently active interfaces.  If a single interface argument is given, it
       displays the status of the given interface only; if a single -a argu-
       ment is given, it displays the status of all interfaces, even those
       that are down.  Otherwise, it configures an interface.


Address Families
       If the first argument after the interface name is recognized as the
       name of a supported address family, that address family is used for
       decoding and displaying all protocol addresses.  Currently supported
       address families include inet (TCP/IP, default), inet6 (IPv6), ax25
       (AMPR Packet Radio), ddp (Appletalk Phase 2), [B]ipx]B\ (Novell IPX) and
       [B]netrom[B] (AMPR Packet radio).

OPTIONS
       -a     display all interfaces which are currently available, even if
              down

       -s     display a short list (like netstat -i)

       -v     be more verbose for some error conditions

       interface
              The name of the interface.  This is usually a driver name fol-
              lowed by a unit number, for example eth0 for the first Ethernet
              interface. If your kernel supports alias interfaces, you can
              specify them with eth0:0 for the first alias of eth0. You can
              use them to assign a second address. To delete an alias inter-
              face use ifconfig eth0:0 down.  Note: for every scope (i.e. same
              net with address/netmask combination) all aliases are deleted,
              if you delete the first (primary).

       up     This flag causes the interface to be activated.  It is implic-
              itly specified if an address is assigned to the interface.

       down   This flag causes the driver for this interface to be shut down.

       [-]arp Enable or disable the use of the ARP protocol on this interface.

       [-]promisc
              Enable or disable the promiscuous mode of the interface.  If
              selected, all packets on the network will be received by the
              interface.

       [-]allmulti
              Enable or disable all-multicast mode.  If selected, all multi-
              cast packets on the network will be received by the interface.

       metric N
              This parameter sets the interface metric.

       mtu N  This parameter sets the Maximum Transfer Unit (MTU) of an inter-
              face.

       dstaddr addr
              Set the remote IP address for a point-to-point link (such as
              PPP).  This keyword is now obsolete; use the pointopoint keyword
              instead.

       netmask addr
              Set the IP network mask for this interface.  This value defaults
              to the usual class A, B or C network mask (as derived from the
              interface IP address), but it can be set to any value.

       add addr/prefixlen
              Add an IPv6 address to an interface.

       del addr/prefixlen
              Remove an IPv6 address from an interface.

       tunnel aa.bb.cc.dd
              Create a new SIT (IPv6-in-IPv4) device, tunnelling to the given
              destination.

       irq addr
              Set the interrupt line used by this device.  Not all devices can
              dynamically change their IRQ setting.

       io_addr addr
              Set the start address in I/O space for this device.

       mem_start addr
              Set the start address for shared memory used by this device.
              Only a few devices need this.

       media type
              Set the physical port or medium type to be used by the device.
              Not all devices can change this setting, and those that can vary
              in what values they support.  Typical values for type are
              10base2 (thin Ethernet), 10baseT (twisted-pair 10Mbps Ethernet),
              AUI (external transceiver) and so on.  The special medium type
              of auto can be used to tell the driver to auto-sense the media.
              Again, not all drivers can do this.

       [-]broadcast [addr]
              If the address argument is given, set the protocol broadcast
              address for this interface.  Otherwise, set (or clear) the
              IFF_BROADCAST flag for the interface.

       [-]pointopoint [addr]
              This keyword enables the point-to-point mode of an interface,
              meaning that it is a direct link between two machines with
              nobody else listening on it.
              If the address argument is also given, set the protocol address
              of the other side of the link, just like the obsolete dstaddr
              keyword does.  Otherwise, set or clear the IFF_POINTOPOINT flag
              for the interface.

       hw class address
              Set the hardware address of this interface, if the device driver
              supports this operation.  The keyword must be followed by the
              name of the hardware class and the printable ASCII equivalent of
              the hardware address.  Hardware classes currently supported
              include ether (Ethernet), ax25 (AMPR AX.25), ARCnet and netrom
              (AMPR NET/ROM).

       multicast
              Set the multicast flag on the interface. This should not nor-
              mally be needed as the drivers set the flag correctly them-
              selves.

       address
              The IP address to be assigned to this interface.

       txqueuelen length
              Set the length of the transmit queue of the device. It is useful
              to set this to small values for slower devices with a high
              latency (modem links, ISDN) to prevent fast bulk transfers from
              disturbing interactive traffic like telnet too much.

NOTES
       Since kernel release 2.2 there are no explicit interface statistics for
       alias interfaces anymore. The statistics printed for the original
       address are shared with all alias addresses on the same device. If you
       want per-address statistics you should add explicit accounting rules
       for the address using the ipchains(8) or iptables(8) command.

       Since net-tools 1.60-4 ifconfig is printing byte counters and human
       readable counters with IEC 60027-2 units. So 1 KiB are 2^10 byte. Note,
       the numbers are truncated to one decimal (which can by quite a large
       error if you consider 0.1 PiB is 112.589.990.684.262 bytes :)

       Interrupt problems with Ethernet device drivers fail with EAGAIN (SIOC-
       SIIFLAGS: Resource temporarily unavailable) it is most likely a inter-
       rupt conflict. See http://www.scyld.com/expert/irq-conflict.html for
       more information.

FILES
       /proc/net/socket
       /proc/net/dev
       /proc/net/if_inet6

BUGS
       While appletalk DDP and IPX addresses will be displayed they cannot be
       altered by this command.

SEE ALSO
       route(8), netstat(8), arp(8), rarp(8), ipchains(8), iptables(8),
       ifup(8), interfaces(5).
       http://physics.nist.gov/cuu/Units/binary.html - Prefixes for binary
       multiples

AUTHORS
       Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
       Alan Cox, <Alan.Cox@linux.org>
       Phil Blundell, <Philip.Blundell@pobox.com>
       Andi Kleen
       Bernd Eckenfels, <net-tools@lina.inka.de>



net-tools                         2007-12-02                       IFCONFIG(8)

One would think that the Slackware man page is older than the Suse one, except for two things:

1. The notes in the Slackware man page refer to how the behavior of ifconfig changed in Linux kernel 2.2. This implies that ifconfig has been maintained after the introduction of kernel 2.0.
2. The synopsis in the Slackware man page refers to a -v option, but the synopsis in the Suse man page does not. This implies that the Slackware man page is aware of a later state of affairs. It could be that the Suse man page accurately documents an older version of ifconfig, and the Slackware man page accurately documents a newer version of ifconfig.

Gerard, this is fascinating. Could you please do a couple of things?

Could you please post the entire man page? I'm interested in the list of authors and the date at the very end, as well as other details in the middle.

Could you also please do this at the command line, and post the response? (Substitute something else for eth0 if eth0 is not up on your system.) If your ifconfig objects to the -v, then we know you're running an ifconfig as documented by the Suse man page; if it takes the -v without complaint, it's more likely you're running an ifconfig as documented by the Slackware man page.

ifconfig -v eth0

[christyyim]

Thanks wje_lf and gerard4143!!!

wje_lf, I think i get what u mean and i really misunderstood the meaning of bytes received. Thanks for your information. And after I insert the wait states, I can get the varying number of bytes (increasing) if i refresh the webpages. I'll modify my source code to take it into consideration. Thanks!!!

and thanks to gerard4143 as well for giving me the updated info. Thanks!!!

[gerard4143]

IFCONFIG( Linux Programmer's Manual IFCONFIG(

DESCRIPTION
Ifconfig is used to configure the kernel-resident network interfaces.
It is used at boot time to set up interfaces as necessary. After that,
it is usually only needed when debugging or when system tuning is
needed.

WARNING: Ifconfig is obsolete on system with Linux kernel newer than
2.0. On this system you should use ip. See the ip manual page for
details

...

AUTHORS
Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
Alan Cox, <Alan.Cox@linux.org>
Phil Blundell, <Philip.Blundell@pobox.com>
Andi Kleen



net-tools 14 August 2000 IFCONFIG(

[gerard4143]

This is the complete man file for ifconfig

"ifconfig -v eth0" is not recognized on my system...so it can't
be included with the standard install...Hope this helps...Gerard4143