Memory layout of a data structure: Difference between revisions
Memory layout of a data structure (view source)
Revision as of 20:06, 8 September 2019
, 4 years agobetter Pascal example
(Scala solution added) |
(better Pascal example) |
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{{task
{{omit from|BBC BASIC}}
It is often useful to control the memory layout of fields in a data structure to match an interface control definition, or to interface with hardware. Define a data structure matching the RS-232 Plug Definition. Use the 9-pin definition for brevity.
Pin Settings for Plug
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Print SizeOf(RS232_Pin9) '' 2 bytes
Sleep</lang>
The FPC (Free Pascal compiler) carefully defines the internal memory structure of data type in its “Programmer’s guide”.
type▼
{$packEnum 2}{$scopedEnums off}
pin = (carrierDetect, receivedData, transmittedData, dataTerminalReady,
signalGround, dataSetReady, requestToSend, clearToSend, ringIndicator);
{$packSet 2}
pins = set of pin;
var▼
signal: pins;
// for demonstration purposes, in order to reveal the memory layout
signalMemoryStructure: word absolute signal;
{$if sizeOf(signal) <> sizeOf(word)} // just as safe-guard
{$fatal signal size}
{$endIf}
begin▼
signal := [];
include(signal, signalGround); // equivalent to signal := signal + [signalGround];
// for demonstration purposes: obviously we know this is always `true`
if signalGround in signal then
begin
writeLn(binStr(signalMemoryStructure, bitSizeOf(signal)));
end;
end.</lang>▼
{{Out}}
<pre>0000000000010000</pre>
=={{header|Go}}==
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=={{header|Pascal}}==
Pascal itself does not define, how data types have to be stored in memory.
It is up to the processor (i. e. compiler) to choose appropriate mechanism.
▲<lang pascal>program memoryLayout;
The [[#Free Pascal|FPC]] (Free Pascal compiler) does predictably define how it stores data.
▲type
▲var
▲begin
▲end.</lang>
=={{header|Perl}}==
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$vec->set($rs232{'RD Received data'}, 1);
$vec->get($rs232{'TC Transmit clock'});</lang>
=={{header|Perl 6}}==
▲{{trans|Pascal}}
The following is specced to work, but implementation of shaped arrays is not quite complete.
<lang perl6>enum T_RS232 <
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println(toOnOff(plug.ringIndicator)) // print value of pin 9 by name
}</lang>
=={{header|Tcl}}==
This Tcl implementation represents the fields as bits in an integer. It provides two functions to get from symbolic pin names to the integer, and vice versa.
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