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.
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 integer | uint8_t * |
"b" | SD_BUS_TYPE_BOOLEAN | boolean | int * (NB: not bool *) |
"n" | SD_BUS_TYPE_INT16 | 16-bit signed integer | int16_t * |
"q" | SD_BUS_TYPE_UINT16 | 16-bit unsigned integer | uint16_t * |
"i" | SD_BUS_TYPE_INT32 | 32-bit signed integer | int32_t * |
"u" | SD_BUS_TYPE_UINT32 | 32-bit unsigned integer | uint32_t * |
"x" | SD_BUS_TYPE_INT64 | 64-bit signed integer | int64_t * |
"t" | SD_BUS_TYPE_UINT64 | 64-bit unsigned integer | uint64_t * |
"d" | SD_BUS_TYPE_DOUBLE | IEEE 754 double precision floating-point | double * |
"s" | SD_BUS_TYPE_STRING | UTF-8 string | const char ** |
"o" | SD_BUS_TYPE_OBJECT_PATH | D-Bus object path string | const char ** |
"g" | SD_BUS_TYPE_SIGNATURE | D-Bus signature string | const char ** |
"h" | SD_BUS_TYPE_UNIX_FD | UNIX file descriptor | int * |
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.