LibVLC logging

libvlc_log_* functions provide access to the LibVLC messages log. More...

Collaboration diagram for LibVLC logging:

Typedefs
typedef struct vlc_log_t	libvlc_log_t
typedef void(*	libvlc_log_cb) (void *data, int level, const libvlc_log_t *ctx, const char *fmt, va_list args)
	Callback prototype for LibVLC log message handler. More...

Enumerations
enum	libvlc_log_level { LIBVLC_DEBUG =0 , LIBVLC_NOTICE =2 , LIBVLC_WARNING =3 , LIBVLC_ERROR =4 }
	Logging messages level. More...

Functions
void	libvlc_log_get_context (const libvlc_log_t *ctx, const char **module, const char **file, unsigned *line)
	Gets log message debug infos. More...
void	libvlc_log_get_object (const libvlc_log_t *ctx, const char **name, const char **header, uintptr_t *id)
	Gets log message info. More...
void	libvlc_log_unset (libvlc_instance_t *p_instance)
	Unsets the logging callback. More...
void	libvlc_log_set (libvlc_instance_t *p_instance, libvlc_log_cb cb, void *data)
	Sets the logging callback for a LibVLC instance. More...
void	libvlc_log_set_file (libvlc_instance_t *p_instance, FILE *stream)
	Sets up logging to a file. More...

Detailed Description

libvlc_log_* functions provide access to the LibVLC messages log.

This is used for logging and debugging.

Typedef Documentation

libvlc_log_cb

typedef void(* libvlc_log_cb) (void *data, int level, const libvlc_log_t *ctx, const char *fmt, va_list args)

Callback prototype for LibVLC log message handler.

Parameters

data	data pointer as given to libvlc_log_set()
level	message level (libvlc_log_level)
ctx	message context (meta-information about the message)
fmt	printf() format string (as defined by ISO C11)
args	variable argument list for the format

Note

Log message handlers must be thread-safe.

Warning

The message context pointer, the format string parameters and the variable arguments are only valid until the callback returns.

libvlc_log_t

typedef struct vlc_log_t libvlc_log_t

Enumeration Type Documentation

libvlc_log_level

enum libvlc_log_level

Logging messages level.

Note

Future LibVLC versions may define new levels.

Enumerator
LIBVLC_DEBUG	Debug message.
LIBVLC_NOTICE	Important informational message.
LIBVLC_WARNING	Warning (potential error) message.
LIBVLC_ERROR	Error message.

Function Documentation

libvlc_log_get_context()

void libvlc_log_get_context	(	const libvlc_log_t *	ctx,
		const char **	module,
		const char **	file,
		unsigned *	line
	)

Gets log message debug infos.

This function retrieves self-debug information about a log message:

• the name of the VLC module emitting the message,
• the name of the source code module (i.e. file) and
• the line number within the source code module.

The returned module name and file name will be NULL if unknown. The returned line number will similarly be zero if unknown.

Parameters

ctx	message context (as passed to the libvlc_log_cb callback)
module	module name storage (or NULL) [OUT]
file	source code file name storage (or NULL) [OUT]
line	source code file line number storage (or NULL) [OUT]

Warning

The returned module name and source code file name, if non-NULL, are only valid until the logging callback returns.

Version

LibVLC 2.1.0 or later

libvlc_log_get_object()

void libvlc_log_get_object	(	const libvlc_log_t *	ctx,
		const char **	name,
		const char **	header,
		uintptr_t *	id
	)

Gets log message info.

This function retrieves meta-information about a log message:

• the type name of the VLC object emitting the message,
• the object header if any, and
• a temporaly-unique object identifier.

This information is mainly meant for manual troubleshooting.

The returned type name may be "generic" if unknown, but it cannot be NULL. The returned header will be NULL if unset; in current versions, the header is used to distinguish for VLM inputs. The returned object ID will be zero if the message is not associated with any VLC object.

Parameters

ctx	message context (as passed to the libvlc_log_cb callback)
name	object name storage (or NULL) [OUT]
header	object header (or NULL) [OUT]
id	temporarily-unique object identifier (or 0) [OUT]

Warning

The returned module name and source code file name, if non-NULL, are only valid until the logging callback returns.

Version

LibVLC 2.1.0 or later

libvlc_log_set()

void libvlc_log_set	(	libvlc_instance_t *	p_instance,
		libvlc_log_cb	cb,
		void *	data
	)

Sets the logging callback for a LibVLC instance.

This function is thread-safe: it will wait for any pending callbacks invocation to complete.

Parameters

cb	callback function pointer
data	opaque data pointer for the callback function

Note

Some log messages (especially debug) are emitted by LibVLC while is being initialized. These messages cannot be captured with this interface.

Warning

A deadlock may occur if this function is called from the callback.

Parameters

p_instance

libvlc instance

Version

LibVLC 2.1.0 or later

libvlc_log_set_file()

void libvlc_log_set_file	(	libvlc_instance_t *	p_instance,
		FILE *	stream
	)

Sets up logging to a file.

Parameters

p_instance	libvlc instance
stream	FILE pointer opened for writing (the FILE pointer must remain valid until libvlc_log_unset())

Version

LibVLC 2.1.0 or later

libvlc_log_unset()

void libvlc_log_unset

(

libvlc_instance_t *

p_instance

)

Unsets the logging callback.

This function deregisters the logging callback for a LibVLC instance. This is rarely needed as the callback is implicitly unset when the instance is destroyed.

Note

This function will wait for any pending callbacks invocation to complete (causing a deadlock if called from within the callback).

Parameters

p_instance

libvlc instance

Version

LibVLC 2.1.0 or later