Provided by: libsystemd-dev_245.4-4ubuntu3.23_amd64 
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 messages lifetime.
Similarly, during the lifetime of such a pointer, the message must not be modified. 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 │ 8bit unsigned │ uint8_t * │
│ │ │ integer │ │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"b" │ SD_BUS_TYPE_BOOLEAN │ boolean │ int * (NB: not bool │
│ │ │ │ *) │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"n" │ SD_BUS_TYPE_INT16 │ 16bit signed │ int16_t * │
│ │ │ integer │ │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"q" │ SD_BUS_TYPE_UINT16 │ 16bit unsigned │ uint16_t * │
│ │ │ integer │ │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"i" │ SD_BUS_TYPE_INT32 │ 32bit signed │ int32_t * │
│ │ │ integer │ │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"u" │ SD_BUS_TYPE_UINT32 │ 32bit unsigned │ uint32_t * │
│ │ │ integer │ │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"x" │ SD_BUS_TYPE_INT64 │ 64bit signed │ int64_t * │
│ │ │ integer │ │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"t" │ SD_BUS_TYPE_UINT64 │ 64bit unsigned │ uint64_t * │
│ │ │ 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 path │ const char ** │
│ │ │ string │ │
├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
│"g" │ SD_BUS_TYPE_SIGNATURE │ D-Bus signature │ const char ** │
│ │ │ 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 0 or a positive integer. 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.
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