Difference between revisions of "Hacker Guide/Variables"

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{{Back to|Hacker Guide}}
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{{Under construction}}
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== Introduction  ==
 
== Introduction  ==
  
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{{VLC}} has a powerful "object variable" infrastructure, that can be used to pass information between modules.
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{{VLC}} has a powerful "object variable" infrastructure, that can be used to pass information between modules.  
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It can be compared to an [[wikipedia:Observer pattern|observer pattern]].
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== Variable Functions  ==
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=== var_Get  ===
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'''va_Get*''' functions will get the value if the variable exists (and will error otherwise).
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var_Get ( vlc_object_t *, const char *, vlc_value_t * );
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var_GetBool( p_obj, psz_name );
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var_GetInteger( p_obj, psz_name );
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var_GetTime( p_obj, psz_name );
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var_GetFloat( p_obj, psz_name );
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var_GetString( p_obj, psz_name );
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var_GetNonEmptyString( p_obj, psz_name );
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var_GetAddress( p_obj, psz_name );
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=== var_Inherit  ===
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'''var_Inherit*''' functions will get the default value (from configuration, for example) or the one set by the parent object.
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This is the function you will want to use most of the time if you are unsure.
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General prototype:
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<type> var_Inherit<type>( vlc_object_t *obj, const char *name );
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You are responsible for freeing any strings used.
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var_Inherit
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var_InheritBool
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var_InheritInteger
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var_InheritFloat
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var_InheritString
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var_InheritTime
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var_InheritAddress
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var_InheritURational
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====Example====
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Reading the "volume-step" configuration option:
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float volumeStep = var_InheritFloat( p_this, "volume-step" );
  
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It can be compared to an [http://en.wikipedia.org/wiki/Observer_pattern Observer Pattern].
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=== var_CreateGet  ===
  
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== Usage  ==
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'''var_CreateGet*''' functions will create the variable and the get the default value if the variable wasn't already created.
  
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var_Get will get the value if the variable exist (error overwise).  
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If the variable does exist before the call it will get the current value (and increment its [[wikipedia:en:Refcount|refcount]]).  
  
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var_Inherit will get the default value or the one setted by the parent object.
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var_Create(a,b,c)
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var_CreateGetInteger(a,b)
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var_CreateGetBool(a,b)
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var_CreateGetTime(a,b)
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var_CreateGetFloat(a,b)
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var_CreateGetString(a,b)
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var_CreateGetNonEmptyString(a,b)
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var_CreateGetAddress(a,b)
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var_CreateGetIntegerCommand(a,b)
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var_CreateGetBoolCommand(a,b)
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var_CreateGetTimeCommand(a,b)
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var_CreateGetFloatCommand(a,b)
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var_CreateGetStringCommand(a,b)
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var_CreateGetNonEmptyStringCommand(a,b)
  
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var_CreateGet will create the variable and the get the default value if the variable wasn't already created. If the varible does exist before the call it will get the current value (and increment the refcount).
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A variable must be created if you want to add a callback or change the value&nbsp;(with <code>var_Set</code>) of a variable <br>
  
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A variable must be created if you want to add a callback or change the value&nbsp;(with var_Set) of a variable <br>
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{{Hacker_Guide}}

Latest revision as of 08:23, 17 April 2019

← Back to Hacker Guide

This page is under construction and may omit important points.

Introduction

VLC media player has a powerful "object variable" infrastructure, that can be used to pass information between modules.

It can be compared to an observer pattern.

Variable Functions

var_Get

va_Get* functions will get the value if the variable exists (and will error otherwise). 

var_Get ( vlc_object_t *, const char *, vlc_value_t * );
var_GetBool( p_obj, psz_name );
var_GetInteger( p_obj, psz_name );
var_GetTime( p_obj, psz_name );
var_GetFloat( p_obj, psz_name );
var_GetString( p_obj, psz_name );
var_GetNonEmptyString( p_obj, psz_name );
var_GetAddress( p_obj, psz_name );

var_Inherit

var_Inherit* functions will get the default value (from configuration, for example) or the one set by the parent object.

This is the function you will want to use most of the time if you are unsure.

General prototype: 

<type> var_Inherit<type>( vlc_object_t *obj, const char *name );

You are responsible for freeing any strings used. 

var_Inherit
var_InheritBool
var_InheritInteger
var_InheritFloat
var_InheritString
var_InheritTime
var_InheritAddress
var_InheritURational

Example

Reading the "volume-step" configuration option: 

float volumeStep = var_InheritFloat( p_this, "volume-step" );

var_CreateGet

var_CreateGet* functions will create the variable and the get the default value if the variable wasn't already created.

If the variable does exist before the call it will get the current value (and increment its refcount). 

var_Create(a,b,c)
var_CreateGetInteger(a,b)
var_CreateGetBool(a,b)
var_CreateGetTime(a,b)
var_CreateGetFloat(a,b)
var_CreateGetString(a,b)
var_CreateGetNonEmptyString(a,b)
var_CreateGetAddress(a,b)
var_CreateGetIntegerCommand(a,b)
var_CreateGetBoolCommand(a,b)
var_CreateGetTimeCommand(a,b)
var_CreateGetFloatCommand(a,b)
var_CreateGetStringCommand(a,b)
var_CreateGetNonEmptyStringCommand(a,b)

A variable must be created if you want to add a callback or change the value (with var_Set) of a variable

This page is part of official VLC media player Documentation (User Guide • Streaming HowTo • Hacker Guide • Modules)
Please read the Documentation Editing Guidelines before you edit the documentation
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
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