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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