Recupera texto en C++ al efectuar system

/*
 * retrieve string response from a command , in linux
 */
#include <stdio.h>

#include <string>
#include <iostream>

#include <sys/syscall.h>   /* Pour les définitions de SYS_xxx */

using namespace std;

string command="ps -aux | grep ttyUSB";

//retrieve string response from a command
string GetStdoutFromCommand(string cmd) {

  string data;
  FILE * stream;
  const int max_buffer = 256;
  char buffer[max_buffer];
  cmd.append(" 2>&1");

  stream = popen(cmd.c_str(), "r");
  if (stream) {
    while (!feof(stream))
      if (fgets(buffer, max_buffer, stream) != NULL) data.append(buffer);
    pclose(stream);
  }
  return data;
}

int main(int argc, char* argv[])
{
string tmp=GetStdoutFromCommand(command);
cout <<tmp<<endl;

}