Re: What is the minimum number of lines to update a gui window without user clicking a button

[Chris Vine <chris cvine freeserve co uk>]

On Sat, 10 Aug 2013 17:53:41 -0400
"L. D. James" <ljames apollo3 com> wrote:
[snip]
> Chris, thanks again for your interest in my question.  I apologize
> for the delayed response, as I was on a support call for most of the
> day. When I got back I trimmed down 500 lines of code to the example
> below.
>
> This is 48 lines of my vpn connection routine. It's 48 out of the 500 
> line application. In those 48 lines I have 4 lines outputting to the 
> console. I would like for those lines to output to a gui window.
>
> Those 4 lines are just some of the actually 25 lines of status that
> will be output in the course of running the application. While it's
> running and checking the connection it outputs either starts "*" or
> dots "." at 10 second interval while it checks some of the file and
> connection status.
>
>
> // code begin
> // -------------------------------------------------
> #include <iostream>
> #include <fstream>
> #include <unistd.h>
> #include <string>
> using namespace std;
> int main(int argc, char* argv[]) {
>      string ret;
>      string server;
>      string command;
>      string runit(string c);
>      setuid(0);
>      server = argv[1];
>      string peerentry = "/etc/ppp/peers/" + server;
>      command = "ls " + peerentry;
>      ret = runit(command);
>      if (ret != peerentry)    {
>          cout << "Problems locating server: " << server << endl; // 
> console out
>          return 1;
>      }
>      string filetest = "/var/run/ppp-" + server + ".pid";
>      ifstream myfile(filetest.c_str());
>
>      if (myfile.is_open()){
>          cout << "Connection is in effect" << endl; // console out
>          myfile.close();
>      }
>      else    {
>          cout << "Connecting to..." << server << endl; // console out
>          command = "pppd call " + server;
>          ret = runit(command);
>          cout << "Results: [" << ret << "]" << endl; // console out
>      }
>      return 0;
> }
> string runit(std::string c){
>      string lret = "";
>      c += " 2>&1";
>      FILE *in;
>      char buff[512];
>      if (!(in = popen(c.c_str(), "r")))    {
>          return lret;
>      }
>      while (fgets(buff, sizeof(buff), in) != NULL)    {
>          lret += buff;
>      }
>      pclose(in);
>      return lret;
> }
> // -------------------------------------------------
> // code end

This appears to be just a batch job calling popen() which brings up a
ppp connection. There is no program loop anywhere and the while
loop for fgets() in runit() will block until EOF is reached, which
equates to the call to pppd ending and the process in which it is
running closing its stdout. Presumably you run this as a cron job, or
something like that? Or, since you say, "while it's running and
checking the connection it outputs either starts '*' or dots '.' at 10
second interval while it checks some of the file and connection status",
possibly you have excised the loop logic, which is the interesting part
for present purposes. (As it happens, it will not compile because the
prototype for runit() is not in namespace scope, but that is no doubt
just a matter of transcription.)

To call up an executable (in this case pppd) in this kind of usage
using glib you would normally use Glib::spawn_async_with_pipes() and
connect to the standard_output and standard_error file descriptors with
Glib::signal_io().connect(). The problem you have got here though is
that you call setuid(0) on a binary which presumably has its suid bit
set in order to launch pppd. You should definitely not do that directly
with a GTK+ program.  You would need to have a small wrapper with suid
set which calls up pppd, which is launched by your GTK+ program using
Glib::spawn_async_with_pipes().  (Yuck.)

As it happens, if you want a short cut for a batch job like this which
provides a GTK+ user interface, I would consider a shell script and
zenity, which is what zenity was intended for.  A google search will
tell you more. However you would still need to circumvent your setuid
problem.

Chris