Use get_decoder_info() ( Use get_decoder_info() ( https://www.libraw.org/docs/API-CXX.html#get_decoder_info ) and check either decoder_name against "nikon_he_load_raw_placeholder()" or decoder_flags bit LIBRAW_DECODER_UNSUPPORTED_FORMAT -- Alex Tutubalin @LibRaw LLC reply
Use get_decoder_info() ( https://www.libraw.org/docs/API-CXX.html#get_decoder_info ) and check either decoder_name against "nikon_he_load_raw_placeholder()" or decoder_flags bit LIBRAW_DECODER_UNSUPPORTED_FORMAT