GStreamer-devel

Init pipeline in the function

Classic

List

Threaded

12 messages Options

Igor Mironchick

Init pipeline in the function

Hi.

I'm a new with gstreamer and glib.

Why can't I init pipeline in function and then use it somewhere else.

Here is the code example:

void initPipeline( GstElement * pipeline )
{
pipeline = gst_pipeline_new( "camera" )
}

void main()
{
GstElement * pipeline;

initPipeline( pipeline );

// And here pipeline == 0 !!! Why?
}

--
Regards,
Igor Mironchick

------------------------------------------------------------------------------

_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

Tristan Matthews-2

Re: Init pipeline in the function

You're passing the pointer by value, you need to pass its address. Also, you need to call gst_init beforehand, so your code should look like:

#include <gst/gst.h>

void initPipeline(GstElement **pipeline)
{
    *pipeline = gst_pipeline_new("camera");
}

int main(int argc, char **argv)
{
    gst_init(&argc, &argv);
    GstElement *pipeline;
    initPipeline(&pipeline);
    return 0;
}

2010/4/22 Igor Mironchick <[hidden email]>

Hi.

I'm a new with gstreamer and glib.

Why can't I init pipeline in function and then use it somewhere else.

Here is the code example:

void initPipeline( GstElement * pipeline )
{
pipeline = gst_pipeline_new( "camera" )
}

void main()
{
GstElement * pipeline;

initPipeline( pipeline );

// And here pipeline == 0 !!! Why?
}

--
Regards,
Igor Mironchick

------------------------------------------------------------------------------

_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

--
Tristan Matthews
email: [hidden email]
web: http://tristanswork.blogspot.com

------------------------------------------------------------------------------

_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

wl2776

Re: Init pipeline in the function

Administrator

In reply to this post by Igor Mironchick

You can't change the function arguments in C, as they are passed by value.
You can, however, pass a pointer (a memory address) to a function, and it can write something to that address. This will cause changing of values of some variables outside the function.

Igor Mironchick wrote

Why can't I init pipeline in function and then use it somewhere else?

You must return the pointer from the function.

Igor Mironchick wrote

Here is the code example:

void initPipeline( GstElement * pipeline )
{
pipeline = gst_pipeline_new( "camera" )
}

void main()
{
GstElement * pipeline;

initPipeline( pipeline );

// And here pipeline == 0 !!! Why?
}

gst_pipeline_new allocates the memory and stores it in the variable pipeline, but this variable is lost when the function returns.

wl2776

Re: Init pipeline in the function

Administrator

wl2776 wrote

You can't change the function arguments in C, as they are passed by value.

I mean, make outside-visible changes of arguments.

Igor Mironchick

Re: Init pipeline in the function

In reply to this post by Tristan Matthews-2

You're passing the pointer by value, you need to pass its address. Also, you need to call gst_init beforehand, so your code should look like:

#include <gst/gst.h>

void initPipeline(GstElement **pipeline)
{
    *pipeline = gst_pipeline_new("camera");
}

int main(int argc, char **argv)
{
    gst_init(&argc, &argv);
    GstElement *pipeline;
    initPipeline(&pipeline);
    return 0;
}

Thx for your reply. I've already found the solution. But a little bit in another way:

void initPipeline( GstElement *& pipeline )
{
pipeline = ...
}

void main()
{
...
GstElement * pipeline;
initPipeline( pipeline );
...
}

--
Regards,
Igor Mironchick

------------------------------------------------------------------------------

_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

giorgio-2

Re: Init pipeline in the function

Try in this Way:

#include <gst/gst.h>

GstElement* initPipeline()
{
return(gst_pipeline_new("camera"));
}

int main(int argc, char **argv)
{
gst_init(&argc, &argv);

GstElement *pipeline = initPipeline();

//
// Now you can use pipeline
//

return 0;
}

Giorgio

Il giorno gio, 22/04/2010 alle 10.58 +0300, Igor Mironchick ha scritto:

>
>
> You're passing the pointer by value, you need to pass its
> address. Also, you need to call gst_init beforehand, so your
> code should look like:
>
> #include <gst/gst.h>
>
> void initPipeline(GstElement **pipeline)
> {
> *pipeline = gst_pipeline_new("camera");
> }
>
> int main(int argc, char **argv)
> {
> gst_init(&argc, &argv);
> GstElement *pipeline;
> initPipeline(&pipeline);
> return 0;
> }
>
> Thx for your reply. I've already found the solution. But a little bit
> in another way:
>
> void initPipeline( GstElement *& pipeline )
> {
> pipeline = ...
> }
>
> void main()
> {
> ...
> GstElement * pipeline;
> initPipeline( pipeline );
> ...
> }
>
>
>
>
> --
> Regards,
> Igor Mironchick
> ------------------------------------------------------------------------------
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

------------------------------------------------------------------------------
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

Kulecz, Walter (JSC-SK)[WYLE INTEG. SCI. & ENG.]

Re: Init pipeline in the function

In reply to this post by Igor Mironchick

uisng:

(* pipeline) = gst_pipeline_new( "camera" );

in initPipeline should work, but I don't see what this extra function call in main() actually buys you.
________________________________________
From: Igor Mironchick [[hidden email]]
Sent: Thursday, April 22, 2010 2:08 AM
To: Discussion of the development of GStreamer
Subject: [gst-devel] Init pipeline in the function

Hi.

I'm a new with gstreamer and glib.

Why can't I init pipeline in function and then use it somewhere else.

Here is the code example:

void initPipeline( GstElement * pipeline )
{
pipeline = gst_pipeline_new( "camera" )
}

void main()
{
GstElement * pipeline;

initPipeline( pipeline );

// And here pipeline == 0 !!! Why?
}

--
Regards,
Igor Mironchick

------------------------------------------------------------------------------
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

Edward Hervey

Re: Init pipeline in the function

Administrator

In reply to this post by Igor Mironchick

The correct answer since nobody was able to come up with it (although
one was very close):

--------------------------------
static GstElement * createPipeline (void) {
GstElement * pipeline;

pipeline = gst_pipeline_new ("mylittleponypipeline");

/* Do stuff with the pipeline, fill it in, etc... */

return pipeline;
}

void main (int argc, gchar **argv) {
GstElement * pipeline;

/* Initialize GStreamer, parse arguments, etc.. */

pipeline = createPipeline ();

/* Use pipeline */
}
---------------------------------------

I recommend everybody who replied to the list to read Kernighan &
Ritchie "The C programming language" [1] as well as reading examples and
learning how to use google.

Edward

[1] http://en.wikipedia.org/wiki/The_C_Programming_Language_%28book%29

On Thu, 2010-04-22 at 10:08 +0300, Igor Mironchick wrote:

> Hi.
>
> I'm a new with gstreamer and glib.
>
> Why can't I init pipeline in function and then use it somewhere else.
>
> Here is the code example:
>
> void initPipeline( GstElement * pipeline )
> {
> pipeline = gst_pipeline_new( "camera" )
> }
>
> void main()
> {
> GstElement * pipeline;
>
> initPipeline( pipeline );
>
> // And here pipeline == 0 !!! Why?
> }
>
> --
> Regards,
> Igor Mironchick
> ------------------------------------------------------------------------------
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

Tristan Matthews-2

Re: Init pipeline in the function

2010/4/23 Edward Hervey <[hidden email]>

The correct answer since nobody was able to come up with it (although
one was very close):

Could you clarify what you considered incorrect in my response?

--------------------------------
static GstElement * createPipeline (void) {
GstElement * pipeline;

pipeline = gst_pipeline_new ("mylittleponypipeline");

/* Do stuff with the pipeline, fill it in, etc... */

return pipeline;
}

void main (int argc, gchar **argv) {
GstElement * pipeline;

/* Initialize GStreamer, parse arguments, etc.. */

pipeline = createPipeline ();

/* Use pipeline */
}
---------------------------------------

I recommend everybody who replied to the list to read Kernighan &
Ritchie "The C programming language" [1] as well as reading examples and
learning how to use google.

Edward

[1] http://en.wikipedia.org/wiki/The_C_Programming_Language_%28book%29

On Thu, 2010-04-22 at 10:08 +0300, Igor Mironchick wrote:
> Hi.
>
> I'm a new with gstreamer and glib.
>
> Why can't I init pipeline in function and then use it somewhere else.
>
> Here is the code example:
>
> void initPipeline( GstElement * pipeline )
> {
> pipeline = gst_pipeline_new( "camera" )
> }
>
> void main()
> {
> GstElement * pipeline;
>
> initPipeline( pipeline );
>
> // And here pipeline == 0 !!! Why?
> }
>
> --
> Regards,
> Igor Mironchick

> ------------------------------------------------------------------------------
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

------------------------------------------------------------------------------
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

Tristan Matthews-2

Re: Init pipeline in the function

2010/4/23 Tristan Matthews <[hidden email]>

2010/4/23 Edward Hervey <[hidden email]>

The correct answer since nobody was able to come up with it (although
one was very close):

Could you clarify what you considered incorrect in my response?

Unless it's a mixed declarations and code issue (C90 and earlier), in which case you'll have to forgive my c++ contaminated style :)

--------------------------------
static GstElement * createPipeline (void) {
GstElement * pipeline;

pipeline = gst_pipeline_new ("mylittleponypipeline");

/* Do stuff with the pipeline, fill it in, etc... */

return pipeline;
}

void main (int argc, gchar **argv) {
GstElement * pipeline;

/* Initialize GStreamer, parse arguments, etc.. */

pipeline = createPipeline ();

/* Use pipeline */
}
---------------------------------------

I recommend everybody who replied to the list to read Kernighan &
Ritchie "The C programming language" [1] as well as reading examples and
learning how to use google.

Edward

[1] http://en.wikipedia.org/wiki/The_C_Programming_Language_%28book%29

On Thu, 2010-04-22 at 10:08 +0300, Igor Mironchick wrote:
> Hi.
>
> I'm a new with gstreamer and glib.
>
> Why can't I init pipeline in function and then use it somewhere else.
>
> Here is the code example:
>
> void initPipeline( GstElement * pipeline )
> {
> pipeline = gst_pipeline_new( "camera" )
> }
>
> void main()
> {
> GstElement * pipeline;
>
> initPipeline( pipeline );
>
> // And here pipeline == 0 !!! Why?
> }
>
> --
> Regards,
> Igor Mironchick

> ------------------------------------------------------------------------------
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

------------------------------------------------------------------------------
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

--
Tristan Matthews
email: [hidden email]
web: http://tristanswork.blogspot.com

Edward Hervey

Re: Init pipeline in the function

Administrator

In reply to this post by Tristan Matthews-2

On Fri, 2010-04-23 at 10:45 -0400, Tristan Matthews wrote:
>
> Could you clarify what you considered incorrect in my response?

You answer was compilable code alright.
Just way too obfuscated for a simple answer which, considering the
basic error the person asking the question did, was much needed :)

Edward

------------------------------------------------------------------------------
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel

Tristan Matthews-2

Re: Init pipeline in the function

2010/4/23 Edward Hervey <[hidden email]>

On Fri, 2010-04-23 at 10:45 -0400, Tristan Matthews wrote:
>
> Could you clarify what you considered incorrect in my response?

You answer was compilable code alright.
Just way too obfuscated for a simple answer which, considering the
basic error the person asking the question did, was much needed :)

Fair enough, I wanted to demonstrate pointer semantics...but a stack overflow link might have been more appropriate.

Best,
Tristan

Edward

------------------------------------------------------------------------------
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel