GTK+3 file chooser in a non-GTK application

I have a C project (on Linux) which does not use GTK at all, but I would like to use GTK only for some specific tasks like selecting a file (file chooser dialog). So I have no GTK parent window, no gtk main loop, etc, I only want a file chooser dialog, which should block the execution of my program till user selected a file (or cancelled) and I don't use GTK then after that ever. What I've tried:

https://developer.gnome.org/gtk3/stable/GtkFileChooserDialog.html

I used the code at "Typical usage", first example. I put gtk_init(&argc, &argv) at the start of my program, and when I need the file chooser, I call a function with code from that example (I use parent as NULL, since there is no parent). The result is a flashing window for a fraction of second, then SIGSEGV. Before that I have this message:

Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.

I already read questions/answers on this message here at stackoverflow, but crashing the application is a more serious thing for me. I've also tried to put this:

gtk_widget_show_all(dialog);

after gtk_file_chooser_dialog_new() which causes no crash, I can select the file, but then I have the SIGSEGV again around gtk_file_chooser_get_filename().

When using gdb, I got this:

Program received signal SIGSEGV, Segmentation fault.
__GI___pthread_mutex_lock (mutex=0x3c3) at ../nptl/pthread_mutex_lock.c:67

Can you help me what mistake I did? I am not familiar with GTK programming too much, so I tried to use examples from the manual, but it does not seem to work. Thanks a lot in advance!

Solution

~~You cannot use widgets without a gtk mainloop.~~

Well, it seems I was wrong. My sincere apologies! I had actually tried to do this before and the conclusions were exactly what I described. But the issue has bugged me for the last days, so I did some more digging and experimenting and came up with the following program:

/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 4; tab-width: 8 -*-  */
/*
 * main.c
 * Copyright (C) 2015 John Coppens <john@jcoppens.com>
 * 
 * standalone_filechooser is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * standalone_filechooser is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdio.h>
#include <gtk/gtk.h>

GtkWidget *
create_filechooser_dialog(char *init_path, GtkFileChooserAction action)
{
  GtkWidget *wdg = NULL;

  switch (action) {
    case GTK_FILE_CHOOSER_ACTION_SAVE:
      wdg = gtk_file_chooser_dialog_new("Save file", NULL, action,
        "Cancel", GTK_RESPONSE_CANCEL,
        "Save", GTK_RESPONSE_OK,
        NULL);
      break;

    case GTK_FILE_CHOOSER_ACTION_OPEN:
      wdg = gtk_file_chooser_dialog_new("Open file", NULL, action,
        "Cancel", GTK_RESPONSE_CANCEL,
        "Open", GTK_RESPONSE_OK,
        NULL);
      break;

    case GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER:
    case GTK_FILE_CHOOSER_ACTION_CREATE_FOLDER:
      break;
  }

  return wdg;
}

int main(int argc, char *argv[])
{
  GtkWidget *wdg;
  char *fname = "";

  if (argc == 2)
    fname = argv[1];

  gtk_init(&argc, &argv);

  wdg = create_filechooser_dialog(fname, GTK_FILE_CHOOSER_ACTION_OPEN);
  if (gtk_dialog_run(GTK_DIALOG(wdg)) == GTK_RESPONSE_OK) {
    printf("%s", gtk_file_chooser_get_filename(GTK_FILE_CHOOSER(wdg)));
    return(0);
  } else  
    return (1);
}

You can call the dialog from another program (or even the terminal) with

standalone_filechooser [default file]

If default file is provided (no brackets), it'll be selected. If a file is selected, it will be printed on stdout, else the program will return with error=1

There is still a small issue with running a widget without main window, which causes a message to be sent to stderr: GtkDialog mapped without a transient parent. This is discouraged. I think this is really a bug (and it might be solved in a more recent version of gtk3). As the message is sent to stderr, it shouldn't interfere with normal use.