Easy way of counting # processeses running?

[ORF]

hello

I needed to count the number of processes (with the same name). I found that this bash script works,

#!/bin/bash
exit $(ps cax | grep firefox | wc -l);

and the exit value can be caught by this code

#include <stdlib.h>   // sytem
#include <iostream> // std::cout, std::endl

int main()
{
  int ret = system("./myBashScript.sh 2>&1 > /dev/null");
  std::cerr << "Number of firefox sessions: " << WEXITSTATUS(ret) << std::endl;
  return 0;
}

This way is dirty and limited to linux.

Can this job be done by a C/C++ routine, non-OS dependent? Or at least, can this job avoid calling "ps cax | grep firefox | wc -l" as an external bash script?

Thank you for your time.

Regards,
ORF

 

[Timo]

Using the snippet from https://stackoverflow.com/questions...nd-get-output-of-command-within-c-using-posix and adapting it to your particular question, an answer to "or at least ..." could be

#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>

std::string exec(const char* cmd) {
    std::array<char, 128> buffer;
    std::string result;
    std::shared_ptr<FILE> pipe(popen(cmd, "r"), pclose);
    if (!pipe) throw std::runtime_error("popen() failed!");
    while (!feof(pipe.get())) {
        if (fgets(buffer.data(), 128, pipe.get()) != nullptr) {
            result += buffer.data();
   }
    }
    return result;
}

int main()
{
  const std::string result = exec("ps cax | grep firefox | wc -l");
  const int nSessions = std::stoi(result);
  std::cerr << "Number of firefox sessions: " << nSessions << std::endl;
  return 0;
}

(I used the c++11 version and changed "std::nullptr" to "nullptr". In the unlikely case your compiler does not support c++11 the stackoverflow page also has a function using older c++ versions).

 

[WWGD]

EDIT What system do you have? In Windows you just go to the Task Manager, " For the rest of us".

 

[Mark44]

EDIT What system do you have? In Windows you just go to the Task Manager, " For the rest of us".

My sense is that OP wants to count processes programmatically.

 

[newjerseyrunner]

Can this job be done by a C/C++ routine, non-OS dependent?

No.
Wait... are you sure that you're doing it right? system() returns the exit code of your script (which should be 0.) You want to get stdout. For this, I recommend using popen(), fgets(), and pclose().

If you want something platform independent, then you need to write something for it:

class Process {
public:
   std::string run(const std::string & cmd){
      //everything below is pseudocode
      #ifdef WIN32
            CreatePipe(&read, &write, &attr, 0);
            CreateProcessA(cmd);
            WaitForSingleObject();
      #else
            pipe = popen(cmd);
            fgets loop;
            pclose(pipe);
      #endif
   }
}

 

[ORF]

Hello

My sense is that OP wants to count processes programmatically.

Yes, that would be the idea

Wait... are you sure that you're doing it right? system() returns the exit code of your script (which should be 0.)

It was a dirty way... the returned value is 0, but you can catch the number of processes using WEXITSTATUS.

Thank you all: the popen/pclose was the proper way of doing it.

Regards!

 

[jim mcnamara]

It is called system programming. Basically you go into kernel mode(windows and linux/unix) and enumerate a data structure called the process_masthead.
Being realistic, I am sure you do not want to do this. For example do you know the system apis and functions involved?
https://blog.codinghorror.com/understanding-user-and-kernel-mode/ Windows only. Unsurprisingly, linux is different. It has kernel mode as well, just to be clear.

As a practical answer, I would go to the GNU (gnu herd) site or the linux kernel site and download the code and spend a month or so learning it. I did this for Solaris 8 long ago and it was very enlightening. The alternative: use system code already in place. sysinternals has good code you can call for all of your system needs on windows -- using the system() method.

https://www.sysinternals.com which is now part of MS technet, some of their process enumeration code was there last time I looked. They have really great standalone executables.