Library initialization/deinitialization

This page details how to initialize and deinitialize libusb. More...

Data Structures
struct	libusb_version
	Structure providing the version of the libusb runtime. More...

Typedefs
typedef struct libusb_context	libusb_context
	Structure representing a libusb session. More...

Enumerations
enum	libusb_log_level {   LIBUSB_LOG_LEVEL_NONE = 0, LIBUSB_LOG_LEVEL_ERROR = 1, LIBUSB_LOG_LEVEL_WARNING = 2, LIBUSB_LOG_LEVEL_INFO = 3,   LIBUSB_LOG_LEVEL_DEBUG = 4 }
	Log message levels. More...
enum	libusb_option { LIBUSB_OPTION_LOG_LEVEL, LIBUSB_OPTION_USE_USBDK }
	Available option values for libusb_set_option(). More...

Functions
void	libusb_set_debug (libusb_context *ctx, int level)
int	libusb_set_option (libusb_context *ctx, enum libusb_option option,...)
	Set an option in the library. More...
int	libusb_init (libusb_context **context)
	Initialize libusb. More...
void	libusb_exit (struct libusb_context *ctx)
	Deinitialize libusb. More...

Detailed Description

This page details how to initialize and deinitialize libusb.

Initialization must be performed before using any libusb functionality, and similarly you must not call any libusb functions after deinitialization.

Typedef Documentation

libusb_context

typedef struct libusb_context libusb_context

Structure representing a libusb session.

The concept of individual libusb sessions allows for your program to use two libraries (or dynamically load two modules) which both independently use libusb. This will prevent interference between the individual libusb users - for example libusb_set_option() will not affect the other user of the library, and libusb_exit() will not destroy resources that the other user is still using.

Sessions are created by libusb_init() and destroyed through libusb_exit(). If your application is guaranteed to only ever include a single libusb user (i.e. you), you do not have to worry about contexts: pass NULL in every function call where a context is required. The default context will be used.

For more information, see Contexts.

Enumeration Type Documentation

libusb_log_level

enum libusb_log_level

Log message levels.

• LIBUSB_LOG_LEVEL_NONE (0) : no messages ever printed by the library (default)
• LIBUSB_LOG_LEVEL_ERROR (1) : error messages are printed to stderr
• LIBUSB_LOG_LEVEL_WARNING (2) : warning and error messages are printed to stderr
• LIBUSB_LOG_LEVEL_INFO (3) : informational messages are printed to stderr
• LIBUSB_LOG_LEVEL_DEBUG (4) : debug and informational messages are printed to stderr

libusb_option

enum libusb_option

Available option values for libusb_set_option().

Enumerator
LIBUSB_OPTION_LOG_LEVEL	Set the log message verbosity. The default level is LIBUSB_LOG_LEVEL_NONE, which means no messages are ever printed. If you choose to increase the message verbosity level, ensure that your application does not close the stderr file descriptor. You are advised to use level LIBUSB_LOG_LEVEL_WARNING. libusb is conservative with its message logging and most of the time, will only log messages that explain error conditions and other oddities. This will help you debug your software. If the LIBUSB_DEBUG environment variable was set when libusb was initialized, this function does nothing: the message verbosity is fixed to the value in the environment variable. If libusb was compiled without any message logging, this function does nothing: you'll never get any messages. If libusb was compiled with verbose debug message logging, this function does nothing: you'll always get messages from all levels.
LIBUSB_OPTION_USE_USBDK	Use the UsbDk backend for a specific context, if available. This option should be set immediately after calling libusb_init(), otherwise unspecified behavior may occur. Only valid on Windows.

Function Documentation

libusb_set_debug()

void libusb_set_debug	(	libusb_context *	ctx,
		int	level
	)

Deprecated:

Use libusb_set_option() instead using the LIBUSB_OPTION_LOG_LEVEL option.

libusb_set_option()

int libusb_set_option	(	libusb_context *	ctx,
		enum libusb_option	option,
			...
	)

Set an option in the library.

Use this function to configure a specific option within the library.

Some options require one or more arguments to be provided. Consult each option's documentation for specific requirements.

Since version 1.0.22, LIBUSB_API_VERSION >= 0x01000106

Parameters

ctx	context on which to operate
option	which option to set
...	any required arguments for the specified option

Returns

LIBUSB_SUCCESS on success

LIBUSB_ERROR_INVALID_PARAM if the option or arguments are invalid

LIBUSB_ERROR_NOT_SUPPORTED if the option is valid but not supported on this platform

libusb_init()

int libusb_init

(

libusb_context **

context

)

Initialize libusb.

This function must be called before calling any other libusb function.

If you do not provide an output location for a context pointer, a default context will be created. If there was already a default context, it will be reused (and nothing will be initialized/reinitialized).

Parameters

context

Optional output location for context pointer. Only valid on return code 0.

Returns

0 on success, or a LIBUSB_ERROR code on failure

See also

libusb_contexts

libusb_exit()

void libusb_exit

(

struct libusb_context *

ctx

)

Deinitialize libusb.

Should be called after closing all open devices and before your application terminates.

Parameters

ctx	the context to deinitialize, or NULL for the default context