Configuration Interface

Overview

The configuration functions and types allow you to read, enumerate, modify and write the contents of ALSA configuration files. More…

// typedefs

typedef struct _snd_config snd_config_t;
typedef struct _snd_config_iterator* snd_config_iterator_t;
typedef struct _snd_config_update snd_config_update_t;

// enums

enum snd_config_type_t;

// structs

struct snd_devname;

// global variables

snd_config_t* snd_config;

// global functions

int
snd_config_top(snd_config_t** config);

int
snd_config_load(
    snd_config_t* config,
    snd_input_t* in
);

int
snd_config_load_override(
    snd_config_t* config,
    snd_input_t* in
);

int
snd_config_save(
    snd_config_t* config,
    snd_output_t* out
);

int
snd_config_update(void);

int
snd_config_update_r(
    snd_config_t** top,
    snd_config_update_t** update,
    const char* path
);

int
snd_config_update_free(snd_config_update_t* update);

int
snd_config_update_free_global(void);

int
snd_config_update_ref(snd_config_t** top);

void
snd_config_ref(snd_config_t* top);

void
snd_config_unref(snd_config_t* top);

int
snd_config_search(
    snd_config_t* config,
    const char* key,
    snd_config_t** result
);

int
snd_config_searchv(
    snd_config_t* config,
    snd_config_t** result,
    ...
);

int
snd_config_search_definition(
    snd_config_t* config,
    const char* base,
    const char* key,
    snd_config_t** result
);

int
snd_config_expand(
    snd_config_t* config,
    snd_config_t* root,
    const char* args,
    snd_config_t* private_data,
    snd_config_t** result
);

int
snd_config_evaluate(
    snd_config_t* config,
    snd_config_t* root,
    snd_config_t* private_data,
    snd_config_t** result
);

int
snd_config_add(
    snd_config_t* config,
    snd_config_t* leaf
);

int
snd_config_delete(snd_config_t* config);

int
snd_config_delete_compound_members(const snd_config_t* config);

int
snd_config_copy(
    snd_config_t** dst,
    snd_config_t* src
);

int
snd_config_make(
    snd_config_t** config,
    const char* key,
    snd_config_type_t type
);

int
snd_config_make_integer(
    snd_config_t** config,
    const char* key
);

int
snd_config_make_integer64(
    snd_config_t** config,
    const char* key
);

int
snd_config_make_real(
    snd_config_t** config,
    const char* key
);

int
snd_config_make_string(
    snd_config_t** config,
    const char* key
);

int
snd_config_make_pointer(
    snd_config_t** config,
    const char* key
);

int
snd_config_make_compound(
    snd_config_t** config,
    const char* key,
    int join
);

int
snd_config_imake_integer(
    snd_config_t** config,
    const char* key,
    const long value
);

int
snd_config_imake_integer64(
    snd_config_t** config,
    const char* key,
    const long long value
);

int
snd_config_imake_real(
    snd_config_t** config,
    const char* key,
    const double value
);

int
snd_config_imake_string(
    snd_config_t** config,
    const char* key,
    const char* ascii
);

int
snd_config_imake_pointer(
    snd_config_t** config,
    const char* key,
    const void* ptr
);

snd_config_type_t
snd_config_get_type(const snd_config_t* config);

int
snd_config_set_id(
    snd_config_t* config,
    const char* id
);

int
snd_config_set_integer(
    snd_config_t* config,
    long value
);

int
snd_config_set_integer64(
    snd_config_t* config,
    long long value
);

int
snd_config_set_real(
    snd_config_t* config,
    double value
);

int
snd_config_set_string(
    snd_config_t* config,
    const char* value
);

int
snd_config_set_ascii(
    snd_config_t* config,
    const char* ascii
);

int
snd_config_set_pointer(
    snd_config_t* config,
    const void* ptr
);

int
snd_config_get_id(
    const snd_config_t* config,
    const char** value
);

int
snd_config_get_integer(
    const snd_config_t* config,
    long* value
);

int
snd_config_get_integer64(
    const snd_config_t* config,
    long long* value
);

int
snd_config_get_real(
    const snd_config_t* config,
    double* value
);

int
snd_config_get_ireal(
    const snd_config_t* config,
    double* value
);

int
snd_config_get_string(
    const snd_config_t* config,
    const char** value
);

int
snd_config_get_ascii(
    const snd_config_t* config,
    char** value
);

int
snd_config_get_pointer(
    const snd_config_t* config,
    const void** value
);

int
snd_config_test_id(
    const snd_config_t* config,
    const char* id
);

snd_config_iterator_t
snd_config_iterator_first(const snd_config_t* node);

snd_config_iterator_t
snd_config_iterator_next(const snd_config_iterator_t iterator);

snd_config_iterator_t
snd_config_iterator_end(const snd_config_t* node);

snd_config_t*
snd_config_iterator_entry(const snd_config_iterator_t iterator);

int
snd_config_get_bool_ascii(const char* ascii);

int
snd_config_get_bool(const snd_config_t* conf);

int
snd_config_get_ctl_iface_ascii(const char* ascii);

int
snd_config_get_ctl_iface(const snd_config_t* conf);

int
snd_names_list(
    const char* iface,
    snd_devname_t** list
);

void
snd_names_list_free(snd_devname_t* list);

int
snd_config_imake_safe_string(
    snd_config_t** config,
    const char* id,
    const char* value
);

// macros

#define SND_CONFIG_DLSYM_VERSION_EVALUATE
#define SND_CONFIG_DLSYM_VERSION_HOOK

#define snd_config_for_each( \
    pos, \
    next, \
    node \
)

Detailed Documentation

The configuration functions and types allow you to read, enumerate, modify and write the contents of ALSA configuration files.

Typedefs

typedef struct _snd_config snd_config_t

Internal structure for a configuration node object.

The ALSA library uses a pointer to this structure as a handle to a configuration node. Applications don’t access its contents directly.

typedef struct _snd_config_iterator* snd_config_iterator_t

Type for a configuration compound iterator.

The ALSA library uses this pointer type as a handle to a configuration compound iterator. Applications don’t directly access the contents of the structure pointed to by this type.

typedef struct _snd_config_update snd_config_update_t

Internal structure for a configuration private update object.

The ALSA library uses this structure to save private update information.

Global Variables

snd_config_t* snd_config

Configuration top-level node (the global configuration).

This variable contains a handle to the top-level configuration node, as loaded from global configuration file.

This variable is initialized or updated by snd_config_update. Functions like snd_pcm_open (that use a device name from the global configuration) automatically call snd_config_update. Before the first call to snd_config_update, this variable is NULL.

The global configuration files are specified in the environment variable ALSA_CONFIG_PATH. If this is not set, the default value is “/usr/share/alsa/alsa.conf”.

Warning

Whenever the configuration tree is updated, all string pointers and configuration node handles previously obtained from this variable may become invalid.

LSB 3.2

Global Functions

int
snd_config_top(snd_config_t** config)

Creates a top level configuration node.

The returned node is an empty compound node without a parent and without an id.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config Handle to the new node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_load(
    snd_config_t* config,
    snd_input_t* in
)

Loads a configuration tree.

The definitions loaded from the input are added to config, which must be a compound node.

Any errors encountered when parsing the input or returned by hooks or functions.

LSB 3.2

Parameters:

config Handle to a top level configuration node.
in Input handle to read the configuration from.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_load_override(
    snd_config_t* config,
    snd_input_t* in
)

Loads a configuration tree and overrides existing configuration nodes.

This function loads definitions from in into config like snd_config_load, but the default mode for input nodes is ‘override’ (!) instead of ‘merge+create’ (+).

Parameters:

config Handle to a top level configuration node.
in Input handle to read the configuration from.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_save(
    snd_config_t* config,
    snd_output_t* out
)

Dumps the contents of a configuration node or tree.

This function writes a textual representation of config’s value to the output out.

-EINVAL A node in the tree has a type that cannot be printed, i.e., SND_CONFIG_TYPE_POINTER.

LSB 3.2

Parameters:

config Handle to the (root) configuration node.
out Output handle.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_update(void)

Updates snd_config by rereading the global configuration files (if needed).

Warning

Whenever snd_config is updated, all string pointers and configuration node handles previously obtained from it may become invalid. For safer operations, use snd_config_update_ref and release the config via snd_config_unref.

Any errors encountered when parsing the input or returned by hooks or functions.

LSB 3.2

Returns:

0 if snd_config was up to date, 1 if snd_config was updated, otherwise a negative error code.

int
snd_config_update_r(
    snd_config_t** top,
    snd_config_update_t** update,
    const char* path
)

Updates a configuration tree by rereading the configuration files (if needed).

The variables pointed to by _top and _update can be initialized to NULL before the first call to this function. The private update information holds information about all used configuration files that allows this function to detects changes to them; this data can be freed with snd_config_update_free.

The global configuration files are specified in the environment variable ALSA_CONFIG_PATH.

Warning

If the configuration tree is reread, all string pointers and configuration node handles previously obtained from this tree become invalid.

Any errors encountered when parsing the input or returned by hooks or functions.

Parameters:

_top Address of the handle to the top-level node.
_update Address of a pointer to private update information.
cfgs A list of configuration file names, delimited with ‘:’. If cfgs is NULL, the default global configuration file is used.

Returns:

0 if _top was up to date, 1 if the configuration files have been reread, otherwise a negative error code.

int
snd_config_update_free(snd_config_update_t* update)

Frees a private update structure.

Parameters:

update The private update structure to free.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_update_free_global(void)

Frees the global configuration tree in snd_config.

This functions releases all resources of the global configuration tree, and sets snd_config to NULL.

LSB 3.2

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_update_ref(snd_config_t** top)

Updates snd_config and takes its reference.

Unlike snd_config_update, this function increases a reference counter so that the obtained tree won’t be deleted until unreferenced by snd_config_unref.

This function is supposed to be thread-safe.

Returns:

0 if snd_config was up to date, 1 if snd_config was updated, otherwise a negative error code.

void
snd_config_ref(snd_config_t* top)

Take the reference of the config tree.

Increases a reference counter of the given config tree.

This function is supposed to be thread-safe.

void
snd_config_unref(snd_config_t* top)

Unreference the config tree.

Decreases a reference counter of the given config tree, and eventually deletes the tree if all references are gone. This is the counterpart of snd_config_unref.

Also, the config taken via snd_config_update_ref must be unreferenced by this function, too.

This function is supposed to be thread-safe.

int
snd_config_search(
    snd_config_t* config,
    const char* key,
    snd_config_t** result
)

Searches for a node in a configuration tree.

This function searches for a child node of config that is identified by key, which contains either the id of a direct child node of config, or a series of ids, separated with dots, where each id specifies a node that is contained in the previous compound node.

In the following example, the comment after each node shows the search key to find that node, assuming that config is a handle to the compound node with id config:

config {
    a 42               # "a"
    b {                # "b"
        c "cee"        # "b.c"
        d {            # "b.d"
            e 2.71828  # "b.d.e"
        }
    }
}
-ENOENT An id in key does not exist.
-ENOENT config or one of its child nodes to be searched is not a compound node.

LSB 3.2

Parameters:

config Handle to the root of the configuration (sub)tree to search.
key Search key: one or more node ids, separated with dots.
result When result!= NULL, the function puts the handle to the node found at the address specified by result.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_searchv(
    snd_config_t* config,
    snd_config_t** result,
    ...
)

Searches for a node in a configuration tree.

This functions searches for a child node of config like snd_config_search, but the search key is the concatenation of all passed search key strings. For example, the call

snd_config_searchv(cfg, &res, "a", "b.c", "d.e", NULL);

is equivalent to the call

snd_config_search(cfg, "a.b.c.d.e", &res);
-ENOENT An id in a search key does not exist.
-ENOENT config or one of its child nodes to be searched is not a compound node.

LSB 3.2

Parameters:

config Handle to the root of the configuration (sub)tree to search.
result When result!= NULL, the function puts the handle to the node found at the address specified by result.
One or more concatenated dot-separated search keys, terminated with NULL.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_search_definition(
    snd_config_t* config,
    const char* base,
    const char* key,
    snd_config_t** result
)

Searches for a definition in a configuration tree, using aliases and expanding hooks and arguments.

This functions searches for a child node of config, allowing aliases and expanding hooks, like snd_config_search_alias_hooks.

If name contains a colon (:), the rest of the string after the colon contains arguments that are expanded as with snd_config_expand.

In any case, result is a new node that must be freed by the caller.

-ENOENT An id in key or an alias id does not exist.
-ENOENT config or one of its child nodes to be searched is not a compound node.

Additionally, any errors encountered when parsing the hook definitions or arguments, or returned by (hook) functions.

Parameters:

config Handle to the configuration (sub)tree to search.
base Implicit key base, or NULL for none.
name Key suffix, optionally with arguments.
result The function puts the handle to the expanded found node at the address specified by result.

Returns:

A non-negative value if successful, otherwise a negative error code.

int
snd_config_expand(
    snd_config_t* config,
    snd_config_t* root,
    const char* args,
    snd_config_t* private_data,
    snd_config_t** result
)

Expands a configuration node, applying arguments and functions.

If config has arguments (defined by a child with id @args), this function replaces any string node beginning with $ with the respective argument value, or the default argument value, or nothing. Furthermore, any functions are evaluated (see snd_config_evaluate). The resulting copy of config is returned in result.

Parameters:

config Handle to the configuration node.
root Handle to the root configuration node.
args Arguments string, can be NULL.
private_data Handle to the private data node for functions.
result The function puts the handle to the result configuration node at the address specified by result.

Returns:

A non-negative value if successful, otherwise a negative error code.

int
snd_config_evaluate(
    snd_config_t* config,
    snd_config_t* root,
    snd_config_t* private_data,
    snd_config_t** result
)

Evaluates a configuration node at runtime.

This function evaluates any functions (@func) in config and replaces those nodes with the respective function results.

Parameters:

config Handle to the source configuration node.
root Handle to the root of the source configuration.
private_data Handle to the private data node for runtime evaluation.
result Must be NULL.

Returns:

A non-negative value if successful, otherwise a negative error code.

int
snd_config_add(
    snd_config_t* config,
    snd_config_t* leaf
)

Adds a child to a compound configuration node.

This function makes the node child a child of the node parent.

The parent node then owns the child node, i.e., the child node gets deleted together with its parent.

child must have an id.

-EINVAL child does not have an id.
-EINVAL child already has a parent.
-EEXIST parent already contains a child node with the same id as child.

LSB 3.2

Parameters:

parent Handle to a compound configuration node.
child Handle to the configuration node to be added.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_delete(snd_config_t* config)

Frees a configuration node.

This function frees a configuration node and all its resources.

If the node is a child node, it is removed from the tree before being deleted.

If the node is a compound node, its descendants (the whole subtree) are deleted recursively.

The function is supposed to be called only for locally copied config trees. For the global tree, take the reference via snd_config_update_ref and free it via snd_config_unref.

LSB 3.2

Parameters:

config Handle to the configuration node to be deleted.

Returns:

Zero if successful, otherwise a negative error code.

See also:

snd_config_remove

int
snd_config_delete_compound_members(const snd_config_t* config)

Deletes the children of a node.

This function removes and frees all children of a configuration node.

Any compound nodes among the children of config are deleted recursively.

After a successful call to this function, config is an empty compound node.

-EINVAL config is not a compound node.

Parameters:

config Handle to the compound configuration node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_copy(
    snd_config_t** dst,
    snd_config_t* src
)

Creates a copy of a configuration node.

This function creates a deep copy, i.e., if src is a compound node, all children are copied recursively.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

dst The function puts the handle to the new configuration node at the address specified by dst.
src Handle to the source configuration node.

Returns:

A non-negative value if successful, otherwise a negative error code.

int
snd_config_make(
    snd_config_t** config,
    const char* key,
    snd_config_type_t type
)

Creates a configuration node.

This functions creates a new node of the specified type. The new node has id id, which may be NULL.

The value of the new node is zero (for numbers), or NULL (for strings and pointers), or empty (for compound nodes).

-ENOMEM Out of memory.

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.
type The type of the new node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_make_integer(
    snd_config_t** config,
    const char* key
)

Creates an integer configuration node.

This function creates a new node of type SND_CONFIG_TYPE_INTEGER and with value 0.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.

Returns:

Zero if successful, otherwise a negative error code.

See also:

snd_config_imake_integer

int
snd_config_make_integer64(
    snd_config_t** config,
    const char* key
)

Creates a 64-bit-integer configuration node.

This function creates a new node of type SND_CONFIG_TYPE_INTEGER64 and with value 0.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.

Returns:

Zero if successful, otherwise a negative error code.

See also:

snd_config_imake_integer64

int
snd_config_make_real(
    snd_config_t** config,
    const char* key
)

Creates a real number configuration node.

This function creates a new node of type SND_CONFIG_TYPE_REAL and with value 0.0.

-ENOMEM Out of memory.

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.

Returns:

Zero if successful, otherwise a negative error code.

See also:

snd_config_imake_real

int
snd_config_make_string(
    snd_config_t** config,
    const char* key
)

Creates a string configuration node.

This function creates a new node of type SND_CONFIG_TYPE_STRING and with value NULL.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.

Returns:

Zero if successful, otherwise a negative error code.

See also:

snd_config_imake_string

int
snd_config_make_pointer(
    snd_config_t** config,
    const char* key
)

Creates a pointer configuration node.

This function creates a new node of type SND_CONFIG_TYPE_POINTER and with value NULL.

-ENOMEM Out of memory.

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.

Returns:

Zero if successful, otherwise a negative error code.

See also:

snd_config_imake_pointer

int
snd_config_make_compound(
    snd_config_t** config,
    const char* key,
    int join
)

Creates an empty compound configuration node.

This function creates a new empty node of type SND_CONFIG_TYPE_COMPOUND.

join determines how the compound node’s id is printed when the configuration is saved to a text file. For example, if the join flag of compound node a is zero, the output will look as follows:

a {
    b "hello"
    c 42
}

If, however, the join flag of a is nonzero, its id will be joined with its children’s ids, like this:

a.b "hello"
a.c 42

An empty compound node with its join flag set would result in no output, i.e., after saving and reloading the configuration file, that compound node would be lost.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.
join Join flag.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_imake_integer(
    snd_config_t** config,
    const char* key,
    const long value
)

Creates an integer configuration node with the given initial value.

This function creates a new node of type SND_CONFIG_TYPE_INTEGER and with value value.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.
value The initial value of the new node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_imake_integer64(
    snd_config_t** config,
    const char* key,
    const long long value
)

Creates a 64-bit-integer configuration node with the given initial value.

This function creates a new node of type SND_CONFIG_TYPE_INTEGER64 and with value value.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.
value The initial value of the new node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_imake_real(
    snd_config_t** config,
    const char* key,
    const double value
)

Creates a real number configuration node with the given initial value.

This function creates a new node of type SND_CONFIG_TYPE_REAL and with value value.

-ENOMEM Out of memory.

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.
value The initial value of the new node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_imake_string(
    snd_config_t** config,
    const char* key,
    const char* ascii
)

Creates a string configuration node with the given initial value.

This function creates a new node of type SND_CONFIG_TYPE_STRING and with a copy of the string value.

-ENOMEM Out of memory.

LSB 3.2

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.
value The initial value of the new node. May be NULL.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_imake_pointer(
    snd_config_t** config,
    const char* key,
    const void* ptr
)

Creates a pointer configuration node with the given initial value.

This function creates a new node of type SND_CONFIG_TYPE_POINTER and with value value.

-ENOMEM Out of memory.

Parameters:

config The function puts the handle to the new node at the address specified by config.
id The id of the new node.
value The initial value of the new node.

Returns:

Zero if successful, otherwise a negative error code.

snd_config_type_t
snd_config_get_type(const snd_config_t* config)

Returns the type of a configuration node.

LSB 3.2

Parameters:

config Handle to the configuration node.

Returns:

The node’s type.

int
snd_config_set_id(
    snd_config_t* config,
    const char* id
)

Sets the id of a configuration node.

This function stores a copy of id in the node.

-EEXIST One of config’s siblings already has the id id.
-EINVAL The id of a node with a parent cannot be set to NULL.
-ENOMEM Out of memory.

Parameters:

config Handle to the configuration node.
id The new node id, must not be NULL.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_set_integer(
    snd_config_t* config,
    long value
)

Changes the value of an integer configuration node.

-EINVAL config is not an integer node.

LSB 3.2

Parameters:

config Handle to the configuration node.
value The new value for the node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_set_integer64(
    snd_config_t* config,
    long long value
)

Changes the value of a 64-bit-integer configuration node.

-EINVAL config is not a 64-bit-integer node.

LSB 3.2

Parameters:

config Handle to the configuration node.
value The new value for the node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_set_real(
    snd_config_t* config,
    double value
)

Changes the value of a real-number configuration node.

-EINVAL config is not a real-number node.

Parameters:

config Handle to the configuration node.
value The new value for the node.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_set_string(
    snd_config_t* config,
    const char* value
)

Changes the value of a string configuration node.

This function deletes the old string in the node and stores a copy of value string in the node.

-EINVAL config is not a string node.

LSB 3.2

Parameters:

config Handle to the configuration node.
value The new value for the node. May be NULL.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_set_ascii(
    snd_config_t* config,
    const char* ascii
)

Changes the value of a configuration node.

This function changes the node’s value to a new value that is parsed from the string ascii. ascii must not be NULL, not even for a string node.

The node’s type does not change, i.e., the string must contain a valid value with the same type as the node’s type. For a string node, the node’s new value is a copy of ascii.

-EINVAL config is not a number or string node.
-EINVAL The value in ascii cannot be parsed.
-ERANGE The value in ascii is too big for the node’s type.
-ENOMEM Out of memory.

LSB 3.2

Parameters:

config Handle to the configuration node.
ascii The new value for the node, as an ASCII string.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_set_pointer(
    snd_config_t* config,
    const void* ptr
)

Changes the value of a pointer configuration node.

This function does not free the old pointer in the node.

-EINVAL config is not a pointer node.

Parameters:

config Handle to the configuration node.
value The new value for the node. May be NULL.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_id(
    const snd_config_t* config,
    const char** value
)

Returns the id of a configuration node.

The returned string is owned by the configuration node; the application must not modify or delete it, and the string becomes invalid when the node’s id changes or when the node is freed.

If the node does not have an id, *id is set to NULL.

LSB 3.2

Parameters:

config Handle to the configuration node.
id The function puts the pointer to the id string at the address specified by id.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_integer(
    const snd_config_t* config,
    long* value
)

Returns the value of an integer configuration node.

-EINVAL config is not an integer node.

LSB 3.2

Parameters:

config Handle to the configuration node.
ptr The node’s value.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_integer64(
    const snd_config_t* config,
    long long* value
)

Returns the value of a 64-bit-integer configuration node.

-EINVAL config is not a 64-bit-integer node.

LSB 3.2

Parameters:

config Handle to the configuration node.
ptr The node’s value.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_real(
    const snd_config_t* config,
    double* value
)

Returns the value of a real-number configuration node.

-EINVAL config is not a real-number node.

Parameters:

config Handle to the configuration node.
ptr The node’s value.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_ireal(
    const snd_config_t* config,
    double* value
)

Returns the value of a real or integer configuration node.

If the node’s type is integer or integer64, the value is converted to the double type on the fly.

-EINVAL config is not a number node.

Parameters:

config Handle to the configuration node.
ptr The node’s value.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_string(
    const snd_config_t* config,
    const char** value
)

Returns the value of a string configuration node.

The returned string is owned by the configuration node; the application must not modify or delete it, and the string becomes invalid when the node’s value changes or when the node is freed.

The string may be NULL.

-EINVAL config is not a string node.

LSB 3.2

Parameters:

config Handle to the configuration node.
ptr The function puts the node’s value at the address specified by ptr.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_ascii(
    const snd_config_t* config,
    char** value
)

Returns the value of a configuration node as a string.

This function dynamically allocates the returned string. The application is responsible for deleting it with free() when it is no longer used.

For a string node with NULL value, the returned string is NULL.

Supported node types are SND_CONFIG_TYPE_INTEGER, SND_CONFIG_TYPE_INTEGER64, SND_CONFIG_TYPE_REAL, and SND_CONFIG_TYPE_STRING.

-EINVAL config is not a (64-bit) integer or real number or string node.
-ENOMEM Out of memory.

LSB 3.2

Parameters:

config Handle to the configuration node.
ascii The function puts the pointer to the returned string at the address specified by ascii.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_get_pointer(
    const snd_config_t* config,
    const void** value
)

Returns the value of a pointer configuration node.

-EINVAL config is not a string node.

Parameters:

config Handle to the configuration node.
ptr The function puts the node’s value at the address specified by ptr.

Returns:

Zero if successful, otherwise a negative error code.

int
snd_config_test_id(
    const snd_config_t* config,
    const char* id
)

Compares the id of a configuration node to a given string.

Parameters:

config Handle to the configuration node.
id ASCII id.

Returns:

The same value as the result of the strcmp function, i.e., less than zero if config’s id is lexicographically less than id, zero if config’s id is equal to id, greater than zero otherwise.

snd_config_iterator_t
snd_config_iterator_first(const snd_config_t* node)

Returns an iterator pointing to a node’s first child.

config must be a compound node.

The returned iterator is valid if it is not equal to the return value of snd_config_iterator_end on config.

Use snd_config_iterator_entry to get the handle of the node pointed to.

LSB 3.2

Parameters:

config Handle to a configuration node.

Returns:

An iterator pointing to config’s first child.

snd_config_iterator_t
snd_config_iterator_next(const snd_config_iterator_t iterator)

Returns an iterator pointing to the next sibling.

The returned iterator is valid if it is not equal to the return value of snd_config_iterator_end on the node’s parent.

Use snd_config_iterator_entry to get the handle of the node pointed to.

LSB 3.2

Parameters:

iterator An iterator pointing to a child configuration node.

Returns:

An iterator pointing to the next sibling of iterator.

snd_config_iterator_t
snd_config_iterator_end(const snd_config_t* node)

Returns an iterator that ends a node’s children list.

config must be a compound node.

The return value can be understood as pointing past the last child of config.

LSB 3.2

Parameters:

config Handle to a configuration node.

Returns:

An iterator that indicates the end of config’s children list.

snd_config_t*
snd_config_iterator_entry(const snd_config_iterator_t iterator)

Returns the configuration node handle pointed to by an iterator.

LSB 3.2

Parameters:

iterator A configuration node iterator.

Returns:

The configuration node handle pointed to by iterator.

int
snd_config_get_bool_ascii(const char* ascii)

Gets the boolean value from the given ASCII string.

Parameters:

ascii The string to be parsed.

Returns:

0 or 1 if successful, otherwise a negative error code.

int
snd_config_get_bool(const snd_config_t* conf)

Gets the boolean value from a configuration node.

Parameters:

conf Handle to the configuration node to be parsed.

Returns:

0 or 1 if successful, otherwise a negative error code.

int
snd_config_get_ctl_iface_ascii(const char* ascii)

Gets the control interface index from the given ASCII string.

Parameters:

ascii The string to be parsed.

Returns:

The control interface index if successful, otherwise a negative error code.

int
snd_config_get_ctl_iface(const snd_config_t* conf)

Gets the control interface index from a configuration node.

Parameters:

conf Handle to the configuration node to be parsed.

Returns:

The control interface index if successful, otherwise a negative error code.

int
snd_names_list(
    const char* iface,
    snd_devname_t** list
)

This function is unimplemented.

Deprecated Since 1.0.14

void
snd_names_list_free(snd_devname_t* list)

This function is unimplemented.

Deprecated Since 1.0.14

Macros

#define SND_CONFIG_DLSYM_VERSION_EVALUATE

dlsym version for the config evaluate callback.

#define SND_CONFIG_DLSYM_VERSION_HOOK

dlsym version for the config hook callback.

#define snd_config_for_each( \
    pos, \
    next, \
    node \
)

Helper macro to iterate over the children of a compound node.

Use this macro like a for statement, e.g.:

snd_config_iterator_t pos, next;
snd_config_for_each(pos, next, node) {
    snd_config_t *entry = snd_config_iterator_entry(pos);
    ...
}

This macro allows deleting or removing the current node.

Parameters:

pos Iterator variable for the current node.
next Temporary iterator variable for the next node.
node Handle to the compound configuration node to iterate over.