# Initializing GStreamer

When writing a GStreamer application, you can simply include `gst/gst.h` to get access to the library functions. Besides that, you will also need to initialize the GStreamer library.

## Simple initialization

Before the GStreamer libraries can be used, `gst_init` has to be called from the main application. This call will perform the necessary initialization of the library as well as parse the GStreamer-specific command line options.

A typical program [1] would have code to initialize GStreamer that looks like this:

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

    int
    main (int   argc,
          char *argv[])
    {
      const gchar *nano_str;
      guint major, minor, micro, nano;

      gst_init (&argc, &argv);

      gst_version (&major, &minor, &micro, &nano);

      if (nano == 1)
        nano_str = "(CVS)";
      else if (nano == 2)
        nano_str = "(Prerelease)";
      else
        nano_str = "";

      printf ("This program is linked against GStreamer %d.%d.%d %s\n",
              major, minor, micro, nano_str);

      return 0;
    }

Use the `GST_VERSION_MAJOR`, `GST_VERSION_MINOR` and `GST_VERSION_MICRO` macros to get the GStreamer version you are building against, or use the function `gst_version` to get the version your application is linked against. GStreamer currently uses a scheme where versions with the same major and minor versions are API- and ABI-compatible.

It is also possible to call the `gst_init` function with two `NULL` arguments, in which case no command line options will be parsed by GStreamer.

## The GOption interface

You can also use a `GOption` table to initialize your own parameters as shown in the next example:

    #include <gst/gst.h>

    int
    main (int   argc,
          char *argv[])
    {
      gboolean silent = FALSE;
      gchar *savefile = NULL;
      GOptionContext *ctx;
      GError *err = NULL;
      GOptionEntry entries[] = {
        { "silent", 's', 0, G_OPTION_ARG_NONE, &silent,
          "do not output status information", NULL },
        { "output", 'o', 0, G_OPTION_ARG_STRING, &savefile,
          "save xml representation of pipeline to FILE and exit", "FILE" },
        { NULL }
      };

      ctx = g_option_context_new ("- Your application");
      g_option_context_add_main_entries (ctx, entries, NULL);
      g_option_context_add_group (ctx, gst_init_get_option_group ());
      if (!g_option_context_parse (ctx, &argc, &argv, &err)) {
        g_print ("Failed to initialize: %s\n", err->message);
        g_clear_error (&err);
        g_option_context_free (ctx);
        return 1;
      }
      g_option_context_free (ctx);

      printf ("Run me with --help to see the Application options appended.\n");

      return 0;
    }

As shown in this fragment, you can use a GOption table to define your application-specific command line options, and pass this table to the GLib initialization function along with the option group returned from the function `gst_init_get_option_group`. Your application options will be parsed in addition to the standard GStreamer options.

1. The code for this example is automatically extracted from the documentation and built under `tests/examples/manual` in the GStreamer tarball.

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