Stream Get Property

Gets the values of stream properties.

Library

Description

The Stream Get Property block gets properties of the stream after the stream is created. The operation of this block is not affected by the blocking mode of the stream connected to its input. Changes to stream properties are reflected immediately.

Limitations

Protocols

Communications protocols generally support only a few, if any, stream properties. Properties are provided to retrieve characteristics of the stream after the stream is created.

Helpful Hints

Other uses of this block

Although it is intended for use with the other Advanced stream blocks, the Stream Get Property block may also be used with the Intermediate stream blocks.

UDP Protocol - Peer Address

The string STREAM_PROPERTY_PEER_ADDRESS property may be used with the UDP protocol to get the IP address and port of the socket's peer.

Input Ports

stm

A reference to the stream created by the Stream Connect or Stream Accept block. If the stream is closed or is otherwise invalid then the negative error code -QERR_INVALID_STREAM is returned by the err output.

Output Ports

stm

A reference to the stream. This output is merely a copy of the stm input. Providing this output makes it much easier to establish the execution order of Stream blocks in the diagram because Simulink generally executes daisy-chained blocks in sequence.

value

This output contains the value(s) of the selected properties. It will be a vector of the same length as the Property code(s) parameter for boolean, integer and double properties. For string properties, it will have a maximum length equal to the Maximum length parameter. If the Use variable-size output option is checked then it will be variable-sized.

err

An int32 value indicating whether the properties were retrieved successfully. It will be zero on success and a negative error code otherwise. See Error Codes for the different error codes and their values. Use the Compare to Error block rather than the error code itself to check for specific error codes. To check for errors in general use the Compare to Zero block to check whether the err output is less than zero.

Data Type Support

The Stream Get Property block only supports signals consistent with the selected property type.

Parameters and Dialog Box

Type of property

The type of property to retrieve. Each property type has its own set of property codes so boolean property "0" is not the same as integer property "0". This parameter should be set first as it affects the property codes that may be selected.

Property code(s) (tunable offline)

A vector of integers specifying the properties to set. Each property of a stream has an associated integer code to identify that property. To select properties based on their name, use the browse button (labelled "...") beside the Property code(s) edit field.

Maximum length

This parameter is only visible when the Type of property is set to string. It specifies the length of the output string. If the Use variable-size output option is checked then it is the maximum length of the output string.

Use variable-size output

This parameter is only visible when the Type of property is set to string. If it is checked then the value output will be a variable-size signal. Otherwise it will be a fixed dimension. The string output may be displayed using the String Display block.

Targets

See Also

• Stream Set Property block
• Stream Listen block
• Stream Connect block
• Stream Write-Read block
• Advanced Communications
• MATLAB Stream Functions
• Communications Using the C Language

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