The type of hpBufferSize is * int in the document, but I checked the header file nppi_statistics_functions.h, it shows that the type of hpBufferSize is size_t * not same as the document.
NppStatus
nppiMeanStdDevGetBufferHostSize_8u_C1R_Ctx(NppiSize oSizeROI, size_t * hpBufferSize/* host pointer */, NppStreamContext nppStreamCtx);
/**
* Buffer size for \ref nppiMean_StdDev_8u_C1R.
*
*/
NppStatus
nppiMeanStdDevGetBufferHostSize_8u_C1R(NppiSize oSizeROI, size_t * hpBufferSize/* host pointer */);
/**
* Buffer size for \ref nppiMean_StdDev_8s_C1R.
*
* For common parameter descriptions, see \ref CommonMeanStdDevGetBufferHostSizeParameters.
*
Image Statistics Functions — npp 12.3 documentation (nvidia.com)