How do you make an object in C? Used in RTOS.

I went through the EE445M and found it’s interesting since the goal of this class is to build a working RTOS. The first lec note mentioned how to make an object in C. The example he used is the “FIFO”.

http://stackoverflow.com/questions/2750270/c-c-struct-vs-class

There are 2 things to learn:

1. “##”: this is called token paste operator, “”is like “…”in MATLAB, just means next line is connected to current line.

2. C doesn’t support OOP (encapsulation, inheritance, polymorphism). In here, we are trying to mimic encapsulation in C.

// macro to create a pointer FIFO
// Comment: NAME is the param to rename the var, functions inside the "class"
#define AddPointerFifo(NAME,SIZE,TYPE,SUCCESS,FAIL) 
TYPE volatile *NAME ## PutPt;    
TYPE volatile *NAME ## GetPt;    
TYPE static NAME ## Fifo [SIZE];        
void NAME ## Fifo_Init(void){ long sr;  
  sr = StartCritical();                 
  NAME ## PutPt = NAME ## GetPt = &NAME ## Fifo[0]; 
  EndCritical(sr);                      
}                                       
int NAME ## Fifo_Put (TYPE data){       
  TYPE volatile *nextPutPt;             
  nextPutPt = NAME ## PutPt + 1;        
  if(nextPutPt == &NAME ## Fifo[SIZE]){ 
    nextPutPt = &NAME ## Fifo[0];       
  }                                     
  if(nextPutPt == NAME ## GetPt ){      
    return(FAIL);                       
  }                                     
  else{                                 
    *( NAME ## PutPt ) = data;          
    NAME ## PutPt = nextPutPt;          
    return(SUCCESS);                    
  }                                     
}                                       
int NAME ## Fifo_Get (TYPE *datapt){    
  if( NAME ## PutPt == NAME ## GetPt ){ 
    return(FAIL);                       
  }                                     
  *datapt = *( NAME ## GetPt ## ++);    
  if( NAME ## GetPt == &NAME ## Fifo[SIZE]){ 
    NAME ## GetPt = &NAME ## Fifo[0];   
  }                                     
  return(SUCCESS);                      
}                                       
unsigned short NAME ## Fifo_Size (void){
  if( NAME ## PutPt < NAME ## GetPt ){  
    return ((unsigned short)( NAME ## PutPt - NAME ## GetPt + (SIZE*sizeof(TYPE)))/sizeof(TYPE)); 
  }                                     
  return ((unsigned short)( NAME ## PutPt - NAME ## GetPt )/sizeof(TYPE)); 
}
// e.g.,
// AddPointerFifo(Rx,32,unsigned char, 1,0)
// SIZE can be any size
// creates RxFifo_Init() RxFifo_Get() and RxFifo_Put()

Ref:

1. lec note of EE 445M

2. http://www.cprogramming.com/reference/preprocessor/token-pasting-operator.html

3. http://complete-concrete-concise.com/programming/c/preprocessor-the-token-pasting-operator

4. http://c.learncodethehardway.org/book/ex19.html