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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | HISTORY | SEE ALSO | NOTES | COLOPHON |
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SD_BUS_M...EAD_BASIC(3) sd_bus_message_read_basic SD_BUS_M...EAD_BASIC(3)
sd_bus_message_read_basic - Read a basic type from a message
#include <systemd/sd-bus.h>
int sd_bus_message_read_basic(sd_bus_message *m, char type,
void *p);
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 unsigned │ uint16_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
│ "i" │ SD_BUS_TYPE_INT32 │ 32-bit signed │ int32_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
│ "u" │ SD_BUS_TYPE_UINT32 │ 32-bit unsigned │ uint32_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
│ "x" │ SD_BUS_TYPE_INT64 │ 64-bit signed │ int64_t * │
│ │ │ integer │ │
├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
│ "t" │ SD_BUS_TYPE_UINT64 │ 64-bit 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 │ const char ** │
│ │ │ path 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.
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.
sd_bus_message_read_basic() was added in version 221.
systemd(1), sd-bus(3), sd_bus_message_append_basic(3),
sd_bus_message_skip(3), sd_bus_message_read(3)
1. D-Bus Specification
http://dbus.freedesktop.org/doc/dbus-specification.html
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨http://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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