参照文档添加了libBaiduSpeechSDK.a静态库，但是运行出现了以下错误。这是什么原因，我应该怎么处理呢

Undefined symbols for architecture arm64:

  "_iconv", referenced from:

      BDS_TTS::doConvert(unsigned char const*, int, unsigned char*, int, void*) in libBaiduSpeechSDK.a(bds_character_coding_iconv.o)

     (maybe you meant: _iconv_canonicalize)

  "_iconv_open", referenced from:

      BDS_TTS::convertCharacterEncoding(unsigned char const*, int, BDS_TTS::BDS_CHARSETS_T, unsigned char**, BDS_TTS::BDS_CHARSETS_T) in libBaiduSpeechSDK.a(bds_character_coding_iconv.o)

  "_iconv_close", referenced from:

      BDS_TTS::convertCharacterEncoding(unsigned char const*, int, BDS_TTS::BDS_CHARSETS_T, unsigned char**, BDS_TTS::BDS_CHARSETS_T) in libBaiduSpeechSDK.a(bds_character_coding_iconv.o)

      BDS_TTS::doConvert(unsigned char const*, int, unsigned char*, int, void*) in libBaiduSpeechSDK.a(bds_character_coding_iconv.o)

ld: symbol(s) not found for architecture arm64

clang: error: linker command failed with exit code 1 (use -v to see invocation)