# sd_bus_message_read_basic

## 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  │ **uint8_t *** │
           │           │                         │ integer         │                 │
           ├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
           │ "b"       │ **SD_BUS_TYPE_BOOLEAN** │ boolean         │ **int ***(NB: not  │
           │           │                         │                 │ **bool ***)         │
           ├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
           │ "n"       │ **SD_BUS_TYPE_INT16** │ 16-bit signed   │ **int16_t *** │
           │           │                         │ integer         │                 │
           ├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
           │ "q"       │ **SD_BUS_TYPE_UINT16** │ 16-bit unsigned │ **uint16_t *** │
           │           │                         │ integer         │                 │
           ├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
           │ "i"       │ **SD_BUS_TYPE_INT32** │ 32-bit signed   │ **int32_t *** │
           │           │                         │ integer         │                 │
           ├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
           │ "u"       │ **SD_BUS_TYPE_UINT32** │ 32-bit unsigned │ **uint32_t *** │
           │           │                         │ integer         │                 │
           ├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
           │ "x"       │ **SD_BUS_TYPE_INT64** │ 64-bit signed   │ **int64_t *** │
           │           │                         │ integer         │                 │
           ├───────────┼─────────────────────────┼─────────────────┼─────────────────┤
           │ "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    │ **const char **** │
           │           │                         │ path 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.
    


## NOTES



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


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