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marian avatar image
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Exception Type='OmmInvalidUsageException' when using fixedWidth in view Array

Most likely something primitive, but I wanted to check our understanding:

when creating a view I thought it was a good practice to set the array size as fixed. It looks as if this is triggering an Exception OmmInvalidUsageException.

Please see below is an example of a simple snapshot request using a view array. Is this normal?

AppClient client; OmmConsumer consumer(OmmConsumerConfig().username("user")); 

//Symbols
OmmArray symbolArray;
{
  symbolArray.addAscii("EUR=");
  symbolArray.complete();
}
//Fields
std::vector<thomsonreuters::ema::access::Int64> fields{11,12,13,22,25};
OmmArray viewArray;
//viewArray.fixedWidth(static_cast<thomsonreuters::ema::access::UInt16>(fields.size())); //With this line we are getting 
//"Exception Type='OmmInvalidUsageException', Text='Unsupported fixedWidth encoding in addInt(). Fixed width='5'. '""
//If commented out everything seems to work fine. Is it normal?
for (auto f : fields)
{
  viewArray.addInt(f);
}
viewArray.complete();
ElementList elemList;
elemList.addArray(thomsonreuters::ema::rdm::ENAME_BATCH_ITEM_LIST, symbolArray);
elemList.addUInt(thomsonreuters::ema::rdm::ENAME_VIEW_TYPE, 1);
elemList.addArray(thomsonreuters::ema::rdm::ENAME_VIEW_DATA, viewArray);
elemList.complete();
ReqMsg test;
//Just a snapshot
consumer.registerClient(ReqMsg().serviceName("hEDD").interestAfterRefresh(false).payload(elemList), client);
elektronrefinitiv-realtimeelektron-sdkema-apirrtelektron-message-apiOMM
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warat.boonyanit avatar image
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Hi @marian

fixedWidth() is not for the size of the array but for the length of each content inside.

By using fixedWidth(X) you basically define that content inside the array cannot be bigger than X bytes.

fixedWidth() is used for decoding optimization and can be omitted.

Edit: "each content"

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marian avatar image marian

Thank you @Warat B. The only thing I do not understand is how it is working when I am setting fixedWidth(2) and requesting only fieldID 22,25, which are clearly bigger in total than 2 bytes. Do you have any idea?

warat.boonyanit avatar image warat.boonyanit marian

Hi @marian

My apologies, It is the length of each content inside the array, not the entire content. I just misread the guide.

By using fixedWidth(2) you basically define that each content inside the array, in this case, the signed int, cannot be bigger than 2 byte, which is –32,768 to 32,767.

marian avatar image marian warat.boonyanit

Thank you @Warat B. and apologies for following up on this, I just want to fully understand it.

In EMA/Src/Access/Include/DataType.h for Data::RealEnum which is used for price I read: 

RealEnum = 8,/*!< An 8-byte precision (19-20 decimal places) fixed-placed representation
of a numeric with either a fractional or exponential part. The range of
a fractional part is 1/2 through 1/256. The range of an exponential
part is 10-14 through 10+7. */

When creating a view with only best bid(fid=22) and best ask (fid=25) each element size is 8 bytes. So, why is it working with fixedWidth(2)?

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