Hacker Guide/Variables

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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

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