sd_bus_message_append_basic - Attach a single field to a message

#include <systemd/sd-bus.h>

int sd_bus_message_append_basic(sd_bus_message *m, char type, const void *p);

sd_bus_message_append_basic() appends a single field to the message m. The parameter type determines how the pointer p is interpreted. type must be one of the basic types as defined by the Basic Types[1] section of the D-Bus specification, and listed in the table below.

Table 1. Item type specifiers

Specifier Constant Description Size Expected C Type
"y" SD_BUS_TYPE_BYTE unsigned integer 1 byte uint8_t
"b" SD_BUS_TYPE_BOOLEAN boolean 4 bytes int
"n" SD_BUS_TYPE_INT16 signed integer 2 bytes int16_t
"q" SD_BUS_TYPE_UINT16 unsigned integer 2 bytes uint16_t
"i" SD_BUS_TYPE_INT32 signed integer 4 bytes int32_t
"u" SD_BUS_TYPE_UINT32 unsigned integer 4 bytes uint32_t
"x" SD_BUS_TYPE_INT64 signed integer 8 bytes int64_t
"t" SD_BUS_TYPE_UINT64 unsigned integer 8 bytes uint64_t
"d" SD_BUS_TYPE_DOUBLE floating-point 8 bytes double
"s" SD_BUS_TYPE_STRING Unicode string variable char[]
"o" SD_BUS_TYPE_OBJECT_PATH object path variable char[]
"g" SD_BUS_TYPE_SIGNATURE signature variable char[]
"h" SD_BUS_TYPE_UNIX_FD UNIX file descriptor 4 bytes int

The value of the parameter is copied into a memory area held by the message object, stays in the possession of the caller and may hence be freely changed after this call without affecting the bus message it has been added to. If
type is "h" (UNIX file descriptor), the descriptor is duplicated by this call and the passed descriptor stays in possession of the caller.

For types "s", "o", and "g", the parameter p is interpreted as a pointer to a NUL-terminated character sequence. As a special case, a NULL pointer is interpreted as an empty string. The string should be valid Unicode string encoded as UTF-8. In case of the two latter types, the additional requirements for a D-Bus object path or type signature should be satisfied. Those requirements should be verified by the recipient of the message.

On success, this call returns 0 or a positive integer. On failure, it returns a negative errno-style error code.

Returned errors may indicate the following problems:


Specified parameter is invalid.


Message has been sealed.


Message is in invalid state.


Message cannot be appended to.


Memory allocation failed.

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file.

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started.

systemd(1), sd-bus(3), sd_bus_message_read_basic(3), sd_bus_message_append(3), The D-Bus specification[2]

Basic Types
The D-Bus specification
systemd 254