View source for Hacker Guide/Variables

{{Back to|Hacker Guide}}

{{Under construction}}

== Introduction  ==

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

It can be compared to an [[wikipedia:Observer pattern|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 [[wikipedia:en:Refcount|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&nbsp;(with <code>var_Set</code>) of a variable <br>

{{Hacker_Guide}}