NAME

       sd_bus_message_read_basic - Read a basic type from a message

SYNOPSIS

       #include <systemd/sd-bus.h>

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

DESCRIPTION

       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 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        │ uint16_t *             │
       │          │                         │ integer                │                        │
       ├──────────┼─────────────────────────┼────────────────────────┼────────────────────────┤
       │"i"       │ SD_BUS_TYPE_INT32       │ 32-bit signed integer  │ int32_t *              │
       ├──────────┼─────────────────────────┼────────────────────────┼────────────────────────┤
       │"u"       │ SD_BUS_TYPE_UINT32      │ 32-bit unsigned        │ uint32_t *             │
       │          │                         │ integer                │                        │
       ├──────────┼─────────────────────────┼────────────────────────┼────────────────────────┤
       │"x"       │ SD_BUS_TYPE_INT64       │ 64-bit signed integer  │ int64_t *              │
       ├──────────┼─────────────────────────┼────────────────────────┼────────────────────────┤
       │"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 path      │ const char **          │
       │          │                         │ string                 │                        │
       ├──────────┼─────────────────────────┼────────────────────────┼────────────────────────┤
       │"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.

RETURN VALUE

       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.

HISTORY

       sd_bus_message_read_basic() was added in version 221.

SEE ALSO

       systemd(1), sd-bus(3), sd_bus_message_append_basic(3), sd_bus_message_skip(3), sd_bus_message_read(3)

NOTES

        1. D-Bus Specification
           https://dbus.freedesktop.org/doc/dbus-specification.html