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/*
* File: direction.cpp
* -------------------
* This file implements the direction.h interface.
*/
#include "direction.h"
#include "error.h"
#include "strlib.h"
#include "tokenscanner.h"
using namespace std;
/*
* Implementation notes: leftFrom, rightFrom, opposite
* ---------------------------------------------------
* These functions use the remainder operator to cycle through the
* internal values of the enumeration type. Note that the leftFrom
* function cannot subtract 1 from the direction because the result
* might then be negative; adding 3 achieves the same effect but
* ensures that the values remain positive.
*/
Direction leftFrom(Direction dir) {
return Direction((dir + 3) % 4);
}
Direction rightFrom(Direction dir) {
return Direction((dir + 1) % 4);
}
Direction opposite(Direction dir) {
return Direction((dir + 2) % 4);
}
/*
* Implementation notes: directionToString
* ---------------------------------------
* The C++ compiler requires the default clause to ensure that this
* function always returns a string, even if the direction is not one
* of the legal values.
*/
string directionToString(Direction dir) {
switch (dir) {
case NORTH: return "NORTH";
case EAST: return "EAST";
case SOUTH: return "SOUTH";
case WEST: return "WEST";
default: return "???";
}
}
/*
* Implementation notes: <<
* ------------------------
* This operator must return the stream by reference after printing
* the value. The operator << returns this stream, so the function
* can be implemented as a single line.
*/
std::ostream & operator<<(std::ostream & os, const Direction & dir) {
return os << directionToString(dir);
}
/*
* Implementation notes: >>
* ------------------------
* This implementation uses the TokenScanner to read tokens from the
* stream.
*/
std::istream & operator>>(std::istream & is, Direction & dir) {
TokenScanner scanner(is);
scanner.ignoreWhitespace();
string token = toUpperCase(scanner.nextToken());
if (token == "") {
dir = Direction(-1);
} else if (startsWith("NORTH", token)) {
dir = NORTH;
} else if (startsWith("EAST", token)) {
dir = EAST;
} else if (startsWith("SOUTH", token)) {
dir = SOUTH;
} else if (startsWith("WEST", token)) {
dir = WEST;
} else {
error("Direction: Unrecognized direction " + token);
}
return is;
}
/*
* Implementation notes: ++
* ------------------------
* The int parameter in the signature for this operator is a marker used
* by the C++ compiler to identify the suffix form of the operator. Note
* that the value after incrementing a variable containing WEST will be
* out of the Direction range. That fact will not cause a problem if
* this operator is used only in the for loop idiom for which it is defined.
*/
Direction operator++(Direction & dir, int) {
Direction old = dir;
dir = Direction(dir + 1);
return old;
}
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