Index · Directives systemd 250


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 section of the D-Bus specification, and listed in the table below.

Table 1. Item type specifiers

SpecifierConstantDescriptionSizeExpected C Type
"y"SD_BUS_TYPE_BYTEunsigned integer1 byteuint8_t
"b"SD_BUS_TYPE_BOOLEANboolean4 bytesint
"n"SD_BUS_TYPE_INT16signed integer2 bytesint16_t
"q"SD_BUS_TYPE_UINT16unsigned integer2 bytesuint16_t
"i"SD_BUS_TYPE_INT32signed integer4 bytesint32_t
"u"SD_BUS_TYPE_UINT32unsigned integer4 bytesuint32_t
"x"SD_BUS_TYPE_INT64signed integer8 bytesint64_t
"t"SD_BUS_TYPE_UINT64unsigned integer8 bytesuint64_t
"d"SD_BUS_TYPE_DOUBLEfloating-point8 bytesdouble
"s"SD_BUS_TYPE_STRINGUnicode stringvariablechar[]
"o"SD_BUS_TYPE_OBJECT_PATHobject pathvariablechar[]
"h"SD_BUS_TYPE_UNIX_FDUNIX file descriptor4 bytesint

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.

Return Value

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.


These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

See Also

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