volatile.cpp

Thinking_in_C___2.rar

//: C08:Volatile.cpp
// From Thinking in C++, 2nd Edition
// at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// The volatile keyword

class Comm {
  const volatile unsigned char byte;
  volatile unsigned char flag;
  enum { bufsize = 100 };
  unsigned char buf[bufsize];
  int index;
public:
  Comm();
  void isr() volatile;
  char read(int Index) const;
};

Comm::Comm() : index(0), byte(0), flag(0) {}

// Only a demo; won't actually work
// as an interrupt service routine:
void Comm::isr() volatile {
  if(flag) flag = 0;
  buf[index++] = byte;
  // Wrap to beginning of buffer:
  if(index >= bufsize) index = 0;
}

char Comm::read(int Index) const {
  if(Index < 0 || Index >= bufsize)
    return 0;
  return buf[Index];
}

int main() {
  volatile Comm Port;
  Port.isr(); // OK
//!  Port.read(0); // Not OK;
                // read() not volatile
} ///:~