1SD_BUS_MESSAGE_READ_BASIC(3)sd_bus_message_read_basiScD_BUS_MESSAGE_READ_BASIC(3)
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NAME

6       sd_bus_message_read_basic - Read a basic type from a message
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SYNOPSIS

9       #include <systemd/sd-bus.h>
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11       int sd_bus_message_read_basic(sd_bus_message *m, char type, void *p);
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DESCRIPTION

14       sd_bus_message_read_basic() reads a basic type from a message and
15       advances the read position in the message. The set of basic types and
16       their ascii codes passed in type are described in the D-Bus
17       Specification[1].
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19       If p is not NULL, it should contain a pointer to an appropriate object.
20       For example, if type is 'y', the object passed in p should have type
21       uint8_t *. If type is 's', the object passed in p should have type
22       const char **. Note that, if the basic type is a pointer (e.g., const
23       char * in the case of a string), the pointer is only borrowed and the
24       contents must be copied if they are to be used after the end of the
25       message's lifetime. Similarly, during the lifetime of such a pointer,
26       the message must not be modified. If type is 'h' (UNIX file
27       descriptor), the descriptor is not duplicated by this call and the
28       returned descriptor remains in possession of the message object, and
29       needs to be duplicated by the caller in order to keep an open reference
30       to it after the message object is freed (for example by calling
31       "fcntl(fd, FD_DUPFD_CLOEXEC, 3)"). See the table below for a complete
32       list of allowed types.
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34       Table 1. Item type specifiers
35       ┌──────────┬─────────────────────────┬─────────────────┬─────────────────┐
36Specifier Constant                Description     Expected C Type 
37       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
38       │"y"       │ SD_BUS_TYPE_BYTE        │ 8bit unsigned   │ uint8_t *       
39       │          │                         │ integer         │                 │
40       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
41       │"b"       │ SD_BUS_TYPE_BOOLEAN     │ boolean         │ int * (NB: not  │
42       │          │                         │                 │ bool *)         │
43       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
44       │"n"       │ SD_BUS_TYPE_INT16       │ 16bit signed    │ int16_t *       
45       │          │                         │ integer         │                 │
46       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
47       │"q"       │ SD_BUS_TYPE_UINT16      │ 16bit unsigned  │ uint16_t *      
48       │          │                         │ integer         │                 │
49       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
50       │"i"       │ SD_BUS_TYPE_INT32       │ 32bit signed    │ int32_t *       
51       │          │                         │ integer         │                 │
52       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
53       │"u"       │ SD_BUS_TYPE_UINT32      │ 32bit unsigned  │ uint32_t *      
54       │          │                         │ integer         │                 │
55       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
56       │"x"       │ SD_BUS_TYPE_INT64       │ 64bit signed    │ int64_t *       
57       │          │                         │ integer         │                 │
58       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
59       │"t"       │ SD_BUS_TYPE_UINT64      │ 64bit unsigned  │ uint64_t *      
60       │          │                         │ integer         │                 │
61       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
62       │"d"       │ SD_BUS_TYPE_DOUBLE      │ IEEE 754 double │ double *        
63       │          │                         │ precision       │                 │
64       │          │                         │ floating-point  │                 │
65       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
66       │"s"       │ SD_BUS_TYPE_STRING      │ UTF-8 string    │ const char **   
67       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
68       │"o"       │ SD_BUS_TYPE_OBJECT_PATH │ D-Bus object    │ const char **   
69       │          │                         │ path string     │                 │
70       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
71       │"g"       │ SD_BUS_TYPE_SIGNATURE   │ D-Bus signature │ const char **   
72       │          │                         │ string          │                 │
73       ├──────────┼─────────────────────────┼─────────────────┼─────────────────┤
74       │"h"       │ SD_BUS_TYPE_UNIX_FD     │ UNIX file       │ int *           
75       │          │                         │ descriptor      │                 │
76       └──────────┴─────────────────────────┴─────────────────┴─────────────────┘
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78       If there is no object of the specified type at the current position in
79       the message, an error is returned.
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RETURN VALUE

82       On success, sd_bus_message_read_basic() returns a positive integer. If
83       the end of the currently opened array has been reached, it returns 0.
84       On failure, it returns a negative errno-style error code.
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86   Errors
87       Returned errors may indicate the following problems:
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89       -EINVAL
90           Specified type string is invalid or the message parameter is NULL.
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92       -ENXIO
93           The message does not contain the specified type at current
94           position.
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96       -EBADMSG
97           The message cannot be parsed.
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SEE ALSO

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

104        1. D-Bus Specification
105           https://dbus.freedesktop.org/doc/dbus-specification.html
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109systemd 253                                       SD_BUS_MESSAGE_READ_BASIC(3)
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