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