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FSX String length, SIMCONNECT_DATATYPE_STRINGV

K

KWB

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69
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germany
Some strings are declared as "variable length", see screenshot below. But when I add them as SIMCONNECT_DATATYPE_STRINGV, I do not get a callback ever when I request data on that particular definition. Providing a fixed length (in the struct and in the AddToDataDefinition) works.

Does not work:
SimConnect_AddToDataDefinition(hSimConnect, DataDefinitionAircraftStringData, "GPS APPROACH AIRPORT ID", NULL, SIMCONNECT_DATATYPE_STRINGV))

Does work:
SimConnect_AddToDataDefinition(hSimConnect, DataDefinitionAircraftStringData, "GPS APPROACH AIRPORT ID", NULL, SIMCONNECT_DATATYPE_STRING32))

This raises three questions:
  1. When is SIMCONNECT_DATATYPE_STRINGV actually used?
  2. As how long do I set such a variable string, to 256, to 260, how do I know? Title is always set to 256 in the examples, do I set GPS APPROACH AIRPORT ID to 256 as well?
  3. Some values have a length different from the predefined enum values, e.g. ATC_ID is specified as length 10, so I would use SIMCONNECT_DATATYPE_STRING32 (closest match) and give away the 22 bytes?
 

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SimConnect_RetrieveString

OK, the answer is the "variable string length example" in the SDK tutorial. The length of the values in the struct does not really matter. Unlike the numeric values (double) the struct does not contain directly the values, but you need to use:

SUCCEEDED(SimConnect_RetrieveString(pData, cbData, &pS->strings, &pszTitle, &cbTitle))

The trick then is to calculate the offset of the next value. Pretty tedious :eek:
 
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