ld: symbol(s) not found for architecture armv7錯誤

將兩個c函數從cpp文件中分離出來單獨放入一個c文件中，報了下面的錯：

Undefined symbols for architecture armv7:
  "MyEncrypt(unsigned char*, int, unsigned char*, int*, unsigned char*)", referenced from:
      MainScene::init() in MainScene.o
  "MyDecrypt(unsigned char*, int, unsigned char*, unsigned char*)", referenced from:
      MainScene::init() in MainScene.o
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)

非常抓狂啊，爲何是Undefined symbols for architecture armv7啊？明明還有arm64的。

最後的錯誤緣由感受跟armv7有點風馬牛不相及，實際上是很簡單的問題，太少寫C代碼了，竟然把這個也忘記了：

If you are using c function in c++ file. you should use extern "c"{}. In .h file

#ifdef __cplusplus
extern "C" 
{
#endif

swrve_currency_given(parameter1, parameter2, parameter3);// a c function

#ifdef __cplusplus
}
#endif