一个文件中定义的整型函数 在另一个文件中调用 要extern吗 include发现这个函数被跳过了 得不到执行
但void的函数就没有这种问题  细节是下边这种 没翻译直接粘贴了
I have two questions, where the first one is about using a typdef union{} in other files, see my code here

  // a.h
  typedef union{
    float vf;
    unsigned char vuc[4];
  }fc4;
  

  // a.c
  fc4 vfc4a;  

  // b.c
  #include "a.h"
  extern fc4 vfc4a;


Compiler gives an error telling fc4 undefined, see it

error: #20: identifier "fc4" is undefined


The second one is about using an integer function in aother file. It is actually another attempt of the one above.

I failed to use the typedef union in other files. Instead, I define a variable of float in file a.c and re-declare it as extern in a global .h file which was included in file b.c, see this.

  // a.c
  fc4 vfc4a;
  float vfa;
  

  int Parsing(void)
  {
    for(int i=0; i<4; i++)
    vfc4a.vuc[i] = RxBuf[i]; // suppose there is a valid RxBuf from the serial

  

  vfa = vfc4a.df;
  printf("%s %f\n", "In parsing()", vfa);
  

  return 1;

  }

  

  // b.c

  #include "global.h"  // extern float vfa in this.
  void a_function(void)
  {

    int ret = Parsing();
    if(ret)
      printf("%s %f\n", "In b.c", vfa);

    for(int i=0; i<4; i++)
      printf("%x ", vfc4a.vuc[i]);
    printf("\n");

  }


printf() is redirected to a serial port sending data to a PC. The PC can receive output given by printf in a_function but cannot receive the one in Parsing(). Besides, vfa in a_function is always 0 including the case that RxBuf is not 0.
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FROM 106.39.0.*