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        │ 8bit unsigned     │ uint8_t *           │
       │          │                         │ integer           │                     │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"b"       │ SD_BUS_TYPE_BOOLEAN     │ boolean           │ int * (NB: not bool │
       │          │                         │                   │ *)                  │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"n"       │ SD_BUS_TYPE_INT16       │ 16bit signed      │ int16_t *           │
       │          │                         │ integer           │                     │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"q"       │ SD_BUS_TYPE_UINT16      │ 16bit unsigned    │ uint16_t *          │
       │          │                         │ integer           │                     │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"i"       │ SD_BUS_TYPE_INT32       │ 32bit signed      │ int32_t *           │
       │          │                         │ integer           │                     │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"u"       │ SD_BUS_TYPE_UINT32      │ 32bit unsigned    │ uint32_t *          │
       │          │                         │ integer           │                     │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"x"       │ SD_BUS_TYPE_INT64       │ 64bit signed      │ int64_t *           │
       │          │                         │ integer           │                     │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"t"       │ SD_BUS_TYPE_UINT64      │ 64bit 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   │ const char **       │
       │          │                         │ string            │                     │
       ├──────────┼─────────────────────────┼───────────────────┼─────────────────────┤
       │"h"       │ SD_BUS_TYPE_UNIX_FD     │ UNIX file         │ int *               │
       │          │                         │ descriptor        │                     │
       └──────────┴─────────────────────────┴───────────────────┴─────────────────────┘

       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.

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