CODEWITHSUNDEEP
cgccffmpeglibavformat
GiuTor
GiuTor

Reputation: 111

Can someone give a clue with those errors from gcc?

I have this code:

#include <stdlib.h>
#include <string.h>
#include <libavcodec/avcodec.h>
#include <libavutil/opt.h>
#include <libavformat/avformat.h>

int main(int argc, char **argv)
{
    avcodec_register_all();
    av_register_all();

    struct AVCodecTag * const *avctag;
    AVOutputFormat *outputFormat = NULL;

    const char *file = "file.mp4";
    outputFormat = av_guess_format(0, file, 0);

    if( ! outputFormat)
    {
        printf ("No container found\n");
        exit (1);
    }
    printf("%s %d\n",outputFormat->long_name,outputFormat->video_codec);

    avctag = outputFormat->codec_tag[0];
    printf("%d\n",avctag->id);
}

The compiler gives this weird error even though I used the -> in the printf line:

error: ‘*avctag’ is a pointer; did you mean to use ‘->’?
  printf("%d\n",avctag->id);

But it gives also a warning: 

warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
  avctag = outputFormat->codec_tag;

AVOutputFormat:codec_tag is defined according to the docs as:

struct AVCodecTag * const *

That is exactly as I defined the pointer above. Can someone give me a clue why I get the warning and the error?

Many thanks

Upvotes: 0

Views: 80

Answers (2)

Chris Turner
Chris Turner

Reputation: 8142

You've got too many * in your declaration.

outputFormat->codec_tag is struct AVCodecTag * const * which means that outputFormat->codec_tag[0] is just struct AVCodecTag const *

or alternative you could do

avctag = outputFormat->codec_tag;
printf("%d\n",avctag[0]->id);

Upvotes: 1

Vlad from Moscow
Vlad from Moscow

Reputation: 310960

The pointer avctag declared ,like a pointer to a constant pointer

struct AVCodecTag * const *avctag;

So this statement

printf("%d\n",avctag->id);

is invalid.

And you need to check the type of the right hand expression in this statement

avctag = outputFormat->codec_tag[0];

What is the type of outputFormat->codec_tag[0]?

Upvotes: 1

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