Many functions in the C API that take in arrays also take in the array size. For example, the C prototype of DAQmxCfgAnlgMultiEdgeStartTrig is :

int32 DAQmxCfgAnlgMultiEdgeStartTrig (TaskHandle taskHandle, const char triggerSources[], int32 triggerSlopeArray[], float64 triggerLevelArray[], uInt32 arraySize);

Here arraySize is just the size of the triggerSlopeArray and triggerLevelArray parameters.

In the gRPC API, the arraySize parameter is not present; the gRPC layer automatically determines the correct value to pass in.

This is also true for most output arrays. For example, the C prototype of DAQmxGetErrorString is:

int32 DAQmxGetErrorString (int32 errorCode, char errorString[], uInt32 bufferSize);

When calling this in C, the convention is to pass in 0 for the bufferSize, and the return value is the required size of the errorString array. Then the caller needs to allocate an array of that size and pass that in in a second call.

In the gRPC API, the gRPC layer will automatically determine the size of most output arrays, so the bufferSize parameter is not present.