--- name: "sd_bus_message_appendv" section: "3" platform: "linux" package: "libsystemd-dev" version: "257.13-1~deb13u1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/sd_bus_message_append" --- # sd\_bus\_message\_appendv(3) Attach fields to a D-Bus message based on a type string Part of [sd\_bus\_message\_append(3)](/sd_bus_message_append/3.md). ## NAME sd\_bus\_message\_append, sd\_bus\_message\_appendv - Attach fields to a D-Bus message based on a type string ## SYNOPSIS ``` #include ``` **int sd\_bus\_message\_append(sd\_bus\_message \****m***, const char \****types***, ...);** **int sd\_bus\_message\_appendv(sd\_bus\_message \****m***, const char \****types***, va\_list** *ap***);** ## DESCRIPTION The **sd\_bus\_message\_append()** function appends a sequence of fields to the D-Bus message object *m*. The type string *types* describes the types of the field arguments that follow. For each type specified in the type string, one or more arguments need to be specified, in the same order as declared in the type string. The type string is composed of the elements shown in the table below. It contains zero or more single "complete types". Each complete type may be one of the basic types or a fully described container type. A container type may be a structure with the contained types, a variant, an array with its element type, or a dictionary entry with the contained types. The type string is **NUL**-terminated. In case of a basic type, one argument of the corresponding type is expected. A structure is denoted by a sequence of complete types between "(" and ")". This sequence cannot be empty — it must contain at least one type. Arguments corresponding to this nested sequence follow the same rules as if they were not nested. A variant is denoted by "v". Corresponding arguments must begin with a type string denoting a complete type, and following that, arguments corresponding to the specified type. An array is denoted by "a" followed by a complete type. Corresponding arguments must begin with the number of entries in the array, followed by the entries themselves, matching the element type of the array. A dictionary is an array of dictionary entries, denoted by "a" followed by a pair of complete types between "{" and "}". The first of those types must be a basic type. Corresponding arguments must begin with the number of dictionary entries, followed by a pair of values for each entry matching the element type of the dictionary entries. **sd\_bus\_message\_appendv()** is equivalent to **sd\_bus\_message\_append()**, except that it is called with a "va\_list" instead of a variable number of arguments. This function does not call the **va\_end()** macro. Because it invokes the **va\_arg()** macro, the value of *ap* is undefined after the call. For further details on the D-Bus type system, please consult the **D-Bus Specification**\[1\]. **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 | | "a" | **SD\_BUS\_TYPE\_ARRAY** | array | determined by array type and size | int, followed by array contents | | "v" | **SD\_BUS\_TYPE\_VARIANT** | variant | determined by the type argument | signature string, followed by variant contents | | "(" | **SD\_BUS\_TYPE\_STRUCT\_BEGIN** | array start | determined by the nested types | structure contents | | ")" | **SD\_BUS\_TYPE\_STRUCT\_END** | array end | | "{" | **SD\_BUS\_TYPE\_DICT\_ENTRY\_BEGIN** | dictionary entry start | determined by the nested types | dictionary contents | | "}" | **SD\_BUS\_TYPE\_DICT\_ENTRY\_END** | dictionary entry end | For types "s" and "g" (unicode string or signature), the pointer may be **NULL**, which is equivalent to an empty string. For "h" (UNIX file descriptor), the descriptor is duplicated by this call and the passed descriptor stays in possession of the caller. See [**sd\_bus\_message\_append\_basic**(3)](/sd_bus_message_append_basic/3.md) for the precise interpretation of those and other types. ## TYPES STRING GRAMMAR ``` types ::= complete_type* complete_type ::= basic_type | variant | structure | array | dictionary basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" | "b" | "h" | "s" | "o" | "g" variant ::= "v" structure ::= "(" complete_type+ ")" array ::= "a" complete_type dictionary ::= "a" "{" basic_type complete_type "}" ``` ## EXAMPLES Append a single basic type (the string "a string"): ``` sd_bus_message *m; ... sd_bus_message_append(m, "s", "a string"); ``` Append all types of integers: ``` uint8_t y = 1; int16_t n = 2; uint16_t q = 3; int32_t i = 4; uint32_t u = 5; int32_t x = 6; uint32_t t = 7; double d = 8.0; sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d); ``` Append a structure composed of a string and a D-Bus path: ``` sd_bus_message_append(m, "(so)", "a string", "/a/path"); ``` Append an array of UNIX file descriptors: ``` sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO); ``` Append a variant, with the real type "g" (signature), and value "sdbusisgood": ``` sd_bus_message_append(m, "v", "g", "sdbusisgood"); ``` Append a dictionary containing the mapping {1=\>"a", 2=\>"b", 3=\>""}: ``` sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL); ``` ## RETURN VALUE On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code. ### Errors Returned errors may indicate the following problems: **-EINVAL** Specified parameter is invalid. **-EPERM** Message has been sealed. **-ESTALE** Message is in invalid state. **-ENXIO** Message cannot be appended to. **-ENOMEM** Memory allocation failed. ## NOTES Functions described here are available as a shared library, which can be compiled against and linked to with the **libsystemd** [**pkg-config**(1)](/pkg-config/1.md) file. The code described here uses [**getenv**(3)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) 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. ## SEE ALSO [**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_message\_append\_basic**(3)](/sd_bus_message_append_basic/3.md), [**sd\_bus\_message\_append\_array**(3)](/sd_bus_message_append_array/3.md), [**sd\_bus\_message\_open\_container**(3)](/sd_bus_message_open_container/3.md) ## NOTES - 1\. D-Bus Specification https://dbus.freedesktop.org/doc/dbus-specification.html#type-system