sd_bus_message_read_basic(3) — Linux manual page
SD_BUS_M...EAD_BASIC(3) sd_bus_message_read_basicSD_BUS_M...EAD_BASIC(3)
NAME
sd_bus_message_read_basic - Read a basic type from a message
SYNOPSIS
#include <systemd/sd-bus.h>
int sd_bus_message_read_basic(sd_bus_message *m, char type,
void *p);
DESCRIPTION
sd_bus_message_read_basic() reads a basic type from a message and
advances the read position in the message. The set of basic types
and their ascii codes passed in type are described in the D-Bus
Specification[1].
If p is not NULL, it should contain a pointer to an appropriate
object. For example, if type is 'y', the object passed in p
should have type uint8_t *. If type is 's', the object passed in
p should have type const char **. Note that, if the basic type is
a pointer (e.g., const char * in the case of a string), the
pointer is only borrowed and the contents must be copied if they
are to be used after the end of the message's lifetime.
Similarly, during the lifetime of such a pointer, the message
must not be modified. If type is 'h' (UNIX file descriptor), the
descriptor is not duplicated by this call and the returned
descriptor remains in possession of the message object, and needs
to be duplicated by the caller in order to keep an open reference
to it after the message object is freed (for example by calling
"fcntl(fd, FD_DUPFD_CLOEXEC, 3)"). See the table below for a
complete list of allowed types.
Table 1. Item type specifiers
┌───────────┬─────────────────────────┬────────────────┬────────────────┐
│ Specifier │ Constant │ Description │ Expected C │
│ │ │ │ Type │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "y" │ SD_BUS_TYPE_BYTE │ 8-bit unsigned │ uint8_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "b" │ SD_BUS_TYPE_BOOLEAN │ boolean │ int * (NB: not │
│ │ │ │ bool *) │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "n" │ SD_BUS_TYPE_INT16 │ 16-bit signed │ int16_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "q" │ SD_BUS_TYPE_UINT16 │ 16-bit │ uint16_t * │
│ │ │ unsigned │ │
│ │ │ integer │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "i" │ SD_BUS_TYPE_INT32 │ 32-bit signed │ int32_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "u" │ SD_BUS_TYPE_UINT32 │ 32-bit │ uint32_t * │
│ │ │ unsigned │ │
│ │ │ integer │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "x" │ SD_BUS_TYPE_INT64 │ 64-bit signed │ int64_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "t" │ SD_BUS_TYPE_UINT64 │ 64-bit │ uint64_t * │
│ │ │ unsigned │ │
│ │ │ integer │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "d" │ SD_BUS_TYPE_DOUBLE │ IEEE 754 │ double * │
│ │ │ double │ │
│ │ │ precision │ │
│ │ │ floating-point │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "s" │ SD_BUS_TYPE_STRING │ UTF-8 string │ const char ** │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "o" │ SD_BUS_TYPE_OBJECT_PATH │ D-Bus object │ const char ** │
│ │ │ path string │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "g" │ SD_BUS_TYPE_SIGNATURE │ D-Bus │ const char ** │
│ │ │ signature │ │
│ │ │ string │ │
├───────────┼─────────────────────────┼────────────────┼────────────────┤
│ "h" │ SD_BUS_TYPE_UNIX_FD │ UNIX file │ int * │
│ │ │ descriptor │ │
└───────────┴─────────────────────────┴────────────────┴────────────────┘
If there is no object of the specified type at the current
position in the message, an error is returned.
RETURN VALUE
On success, sd_bus_message_read_basic() returns a positive
integer. If the end of the currently opened array has been
reached, it returns 0. On failure, it returns a negative
errno-style error code.
Errors
Returned errors may indicate the following problems:
-EINVAL
Specified type string is invalid or the message parameter is
NULL.
-ENXIO
The message does not contain the specified type at current
position.
-EBADMSG
The message cannot be parsed.
HISTORY
sd_bus_message_read_basic() was added in version 221.
SEE ALSO
systemd(1), sd-bus(3), sd_bus_message_append_basic(3),
sd_bus_message_skip(3), sd_bus_message_read(3)
NOTES
1. D-Bus Specification
https://dbus.freedesktop.org/doc/dbus-specification.html
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systemd 257~devel SD_BUS_M...EAD_BASIC(3)
Pages that refer to this page: sd-bus(3), sd_bus_message_append_basic(3), sd_bus_message_read(3), sd_bus_message_skip(3), systemd.directives(7), systemd.index(7)