error LNK2019，cpp文件调用C代码

/*******************************/
Interface.h -- cpp file call C code

version 1.0.8, Mar 29th, 2016

Copyright (C) 2015-2016 Acheld CHEN

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

//
#ifndef _INTERFACE_FFMPEG_H_
#define _INTERFACE_FFMPEG_H_
#include "CInlineCode.h"

#ifdef __cplusplus
extern "C" {
#endif
int main_decoding_encoding(int argc, char **argv);
int main_demuxing_decoding (int argc, char **argv);
int main_filtering_audio(int argc, char **argv);
int main_avio_dir_cmd(int argc, char *argv[]);
int main_metadata (int argc, char **argv);
int main_avio_reading(int argc, char *argv[]);
int main_filter_audio(int argc, char *argv[]);
int main_extract_mvs(int argc, char **argv);
int main_filtering_video(int argc, char **argv);
int main_http_multiclient(int argc, char **argv);

#ifdef __cplusplus
}
#endif
//error LNK2019: 无法解析的外部符号
//"int __cdecl main_decoding_encoding(int,char * *)" (?main_decoding_encoding@@YAHHPAPAD@Z)，
//该符号在函数 _main 中被引用
//int main_decoding_encoding(int argc, char **argv);

#endif


extern "C" ，编译时按照C代码的编译规则进行编译