Type Definition alsa_sys::snd_ctl_elem_list_t

type snd_ctl_elem_list_t = _snd_ctl_elem_list;

CTL element list container

This is a list of CTL elements. The list contains management information (e.g. how many elements the sound card has) as well as the element identifiers. All functions which operate on the list are named snd_ctl_elem_list_*().

\par Memory management

There are two memory areas to deal with: The list container itself and the memory for the element identifiers.

To manage the area for the list container, the following functions are used:

• snd_ctl_elem_list_malloc() / snd_ctl_elem_list_free() to allocate and free memory on the heap, or
• snd_ctl_elem_list_alloca() to allocate the memory on the stack. This memory is auto-released when the stack is unwound.

To manage the space for the element identifiers, the snd_ctl_elem_list_alloc_space() and snd_ctl_elem_list_free_space() are used. Allocating the right amount of space can be achieved by first obtaining the number of elements and then calling snd_ctl_elem_list_alloc_space():

\code snd_ctl_elem_list_t* list; int count;

// Initialise list snd_ctl_elem_list_malloc(&list);

// Get number of elements snd_ctl_elem_list(ctl, list); count = snd_ctl_elem_list_get_count(list);

// Allocate space for identifiers snd_ctl_elem_list_alloc_space(list, count);

// Get identifiers snd_ctl_elem_list(ctl, list); // yes, this is same as above :)

// Do something useful with the list...

// Cleanup snd_ctl_elem_list_free_space(list); snd_ctl_elem_list_free(list); \endcode

\par The Elements

The elements in the list are accessed using an index. This index is the location in the list; Don't confuse it with the 'index' of the element identifier. For example:

\code snd_ctl_elem_list_t list; unsigned int element_index;

// Allocate space, fill list ...

element_index = snd_ctl_elem_list_get_index(&list, 2);

\endcode

This will access the 3rd element in the list (index=2) and get the elements index from the driver (which might be 13, for example).