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• Go / Cgo - How to access a field of a Cstruct ?

  17 août 2021, par ChrisG

  I develope an application in Go for transcode an audio file from one format to another one :

  


  I use the goav library that use Cgo to bind the FFmpeg C-libs :
https://github.com/giorgisio/goav/

  


  ---

  


  The goav library ; package avformat has a typedef that cast the original FFmpeg lib C-Struct AVOutputFormat :

  


  type ( 
   OutputFormat               C.struct_AVOutputFormat
)


  


  In my code i have a variable called outputF of the type OutputFormat that is a C.struct_AVOutputFormat.

  


  The C real AVOutputFormat struct has fields :

  


  name, long_name, mime_type, extensions, audio_codec, video_codec, subtitle_codec,..


  


  and many fields more.

  


  See : https://ffmpeg.org/doxygen/2.6/structAVOutputFormat.html

  


  ---

  


  I verified the situation by fmt.Println(outputF) and reached :

  


  {0x7ffff7f23383 0x7ffff7f23907 0x7ffff7f13c33 0x7ffff7f23383 86017 61 0 128 <nil> 0x7ffff7f8cfa0 <nil> 3344 0x7ffff7e3ec10 0x7ffff7e3f410 0x7ffff7e3ecc0 <nil> 0x7ffff7e3dfc0 <nil> <nil> <nil> <nil> <nil> <nil> 0 0x7ffff7e3e070 0x7ffff7e3e020 <nil>}&#xA;</nil></nil></nil></nil></nil></nil></nil></nil></nil></nil>

  


  The audio codec field is on position 5 and contains 86017

  


  I verified the field name by using the package reflect :

  


  val := reflect.Indirect(reflect.ValueOf(outputF))
fmt.Println(val)
fmt.Println("Fieldname: ", val.Type().Field(4).Name)

Output:
Fieldname:  audio_codec


  


  ---

  


  I try to access the field audio_codec of the original AVOutputFormat using :

  


  fmt.Println(outputF.audio_codec)
ERROR: outputF.audio_codec undefined (cannot refer to unexported field or method audio_codec)


fmt.Println(outputF._audio_codec)
ERROR: outputF._audio_codec undefined (type *avformat.OutputFormat has no field or method _audio_codec)


  


  


  As i read in the Cgo documentation :
Within the Go file, C's struct field names that are keywords in Go can be accessed by prefixing them with an underscore : if x points at a C struct with a field named "type", x._type accesses the field. C struct fields that cannot be expressed in Go, such as bit fields or misaligned data, are omitted in the Go struct, replaced by appropriate padding to reach the next field or the end of the struct.

  


  


  But I have no idea what im doing wrong.

  


  Edit :
Okay for sure no underscore is required as audio_codec is not a keyword in Go. This i understood for now. But still there is the question why im not able to access the CStruct field "audio_codec".

  


• Where to (long time) host Spring Boot Application with Data Base Backup and Linux Root Access [closed]

  22 mai 2024, par Lord Helmchen

  I developed a small application for my father. It uses Spring Boot, MySQL and FFMPEG, which I currently installed on Linux.

  


  I want to host it, deploy it automatically, have a back up and root access for FFMPEG installation.

  


  It runs smoothly locally on Windows / Linux, now I want to host it somewhere.

  


  What I would like to have :

  


  

  • Ease of deployment : I got experience in adminstration of linux root servers, but I look for something easy to integrate and maybe automatically deploy it from Github or Gitlab

  


  • Backup : I want to backup the database ideally to another service provider in case something goes wrong.

  


  • Linux : One Part of it, amongs others is to convert different audio formats using ffmpeg.
So, (I think) I need linux root access as well.

  


  • Time Horzion : I would like to make sure it still runs in ten+ years, so it should be a reliable provider where I only update the application from time to time if needed.

  


  • Money : As it is only for personal use at this moment, I don't want to invest a fortune.

  


  


  What provider and deployment pipeline would you recommend to me ?

  


• Revision fe533c9741 : Merge "Change to prevent invalid memory access"

  24 septembre 2013, par Yaowu Xu

  Changed Paths :
   Modify /vp9/encoder/vp9_encodeframe.c

  
  
  Merge "Change to prevent invalid memory access"