Redirecting I/O

Hi everyone,

Did anyone know how to communicate between C program and a GUI program?

example :

If i have a C program which does all the operation. And a GUI program written in GTK which provides all the nice interface for the C program.

The C program and GTK program are two separate program.....
which means that C program is runnable through command line without the need of the GUI.

However if i want to make both of them communicate in term of messages. For example, usually the error messages is displayed in the terminal / console..but when i am using a GUI as a front end to run the C program, the error message will be display in the window in the GUI program instead of in the console....

Is there a way to send over the message from C program to GUI?

Anyone got example or sample code?

Thank you.

Happy coding.....

man popen

Yes it very possible.
In Linux, I think you shoudl use the dup() functions... I don't know that APi very well.
In windows:
Call VOID GetStartupInfo(); to get your default startup information. Then start your console app with CreateProcess function, and send you GUI input/output handles to the console app.

Code:

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STARTUPINFO si;
PROCESS_INFORMATION pi;
GetStartupInfo(&si);
//one's output is another's input
HANDLE temp = si.hStdInput;
si.hStdInput = si.hStdOutput;
si.hStdOutput = temp;
CreateProcess("consoleapp.exe","command lines",0,0,TRUE,0,0,0,&si,&pi);

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I think this would work, although I don't know if the handles can be inherited, nor I know if that HANDLE switching is safe.

xEarth, man! What a hell are you talking about? You can retrieve standard handles from STARTUPINFO if and only if dwFlags is set to STARTF_USESTDHANDLES. So to retrieve them you must allways use GetStdHandle(); And you haven't set fields cb, dwFlags and hStdError. Not to mention you are using C++ compiler again...:(
This _corrected_ program will redirect all streams of "program.exe" to itself:

Code:

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#include <windows.h>
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    STARTUPINFO si;
    PROCESS_INFORMATION pi;

    ZeroMemory(&si, sizeof(si));
    ZeroMemory(&pi, sizeof(pi));

    si.cb        = sizeof(si);
    si.dwFlags    = STARTF_USESTDHANDLES;
    si.hStdInput  = GetStdHandle(STD_INPUT_HANDLE);
    si.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
    si.hStdError  = GetStdHandle(STD_ERROR_HANDLE);

    if (!CreateProcess("program.exe", NULL, NULL, NULL,
                      TRUE, 0, NULL, NULL, &si, &pi))
    {
        printf("CreateProcess() failed!\n");
        exit(EXIT_FAILURE);
    }

    WaitForSingleObject(pi.hProcess, INFINITE);

    CloseHandle(pi.hProcess);
    CloseHandle(pi.hThread);

    return 0;
}

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BTW. sorry suwie, I know it have nothing to do with what you wanted to know.

I wrote that in the reply text box.. I've not compiled nor tested... And I know for sure that my code isn't reliable.. I only intended with that to show a little example. And If a non-console process is started, yes, one must get the standard handles to the console, because none was instantiated.
About field cb, it's set...

Code:

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GetStartupInfo(&si);

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Plus... C++ where???

Quote:

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Originally Posted by xErath

I wrote that in the reply text box.. I've not compiled nor tested... And I know for sure that my code isn't reliable.. I only intended with that to show a little example. And If a non-console process is started, yes, one must get the standard handles to the console, because none was instantiated.
About field cb, it's set...

Code:

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GetStartupInfo(&si);

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Plus... C++ where???

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You have declarations of more variables after statements start. The list of windows compilers that support C99 to any extent is rather short...

I apologize in advance as I have never actually programmed on a Unix box... but I am pretty sure this does the trick. I'd compile and test if I had a Unix box =/

Code:

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// remember to #include headers, i haven't done that

int main (int argc, char **argv)
{
  int tnout[2]; // write pipe to the child
  int tnin[2];  // read pipe from the child

  pid_t childp;


  if (pipe (tnout) || pipe (tnin))
  {
    fprintf (stderr, "Not enough file handles!\n");
    exit (EXIT_FAILURE);
  }

  childp = fork ();

  if (childp == -1)
  {
    fprintf (stderr, "Out of memory!\n");
    exit (EXIT_FAILURE);
  }

  else if (childp == 0)
  { // child process
    // close the unused pipe-ends
    close (tnout[1]);
    close (tnin[0]);

    // set stdin, stdout, to the open pipe ends
    dup2 (tnout[0], 0);
    dup2 (tnin[1], 1);

    // start child program
    // replace "telnet localhost 23" with whatever program
    // you wish to call and whichever exec* is convienent
    execl ("telnet", "telnet", "localhost", "23", (char *) 0);
    // shouldn't return
    fprintf (stderr, "Couldn't start telnet!\n");
    exit (EXIT_FAILURE);
  }

  // parent process
 
  // tnout[1] can be used to write to the child's stdin
  close (tnout[0]);
  // tnin[0] can be used to read from the child's stdout
  close (tnin[1]);

  return 0;
}

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