C++ 연산자 오버로딩 - 첨자 연산자 오버로딩

Vector를 이용한 첨자 연산

#include <iostream>

using namespace std;

class Vector {
public:
	float x, y, z;

	Vector(float x, float y, float z)
		: x(x), y(y), z(z) {

	}

	float operator[](int idx) const {
		if (idx < 1)
			return x;
		if (idx == 1)
			return y;
		return z;
	}
	// 첨자는 외부에서 수정을 하려면 함수를 2개 만들어야한다.
	float& operator[](int idx) {
		if (idx < 1)
			return x;
		if (idx == 1)
			return y;
		return z;
	}
};

int main() {
	Vector v{ 1, 2, 3 };
	cout << v[-1] << endl;
	cout << v[0] << endl;
	cout << v[1] << endl;
	cout << v[2] << endl;
	cout << v[3] << endl;

	v[1] = 100;

	cout << v[1] << endl;
}

• 실행 결과

  1
  1
  2
  3
  3
  100

문자열을 이용한 첨자 연산

#include <iostream>
#include <cstring>

using namespace std;

class String {
private:
	char* _chars;

public:
	String(const char* chars)
		: _chars(new char[strlen(chars) + 1]) {
		strcpy(_chars, chars);
	}

	char operator[](int idx) const {
		return _chars[idx];
	}

	char& operator[](int idx) {
		return _chars[idx];
	}

	friend ostream& operator<<(ostream& os, const String& s) {
		os << s._chars;
		return os;
	}
};

int main() {
	String s("abc");
	
	cout << s[0] << endl;
	s[0] = 'b';
	s[2] = 'q';

	cout << s << endl;
}

• 실행 결과

  a
  bbq

hashtable을 이용한 첨자 연산

#include <iostream>
#include <vector>

using namespace std;

using Key = string;
using Value = string;
using KeyValue = pair<string, string>;

class Bucket {
private:
	vector<KeyValue> _items;

public:
	Value& get(const Key& key) {
		for (KeyValue& keyValue : _items) {
			if (keyValue.first == key) {
				return keyValue.second;
			}
		}
		_items.push_back(std::make_pair(key, Value()));
		return _items.back().second;
	}
};

class HashTable {
private:
	vector<Bucket> _buckets;
	// 원형 : vector<vector<pair<string, string>>> _buckets;
	int hash(const Key& key) const {
		int h = 0;
		for (char ch : key)
			h += ch;
		return h;
	}
public:
	HashTable(int size = 100)
		: _buckets(vector<Bucket>(size)) {

	}

	Value& operator[](Key key) {
		int bucketidx = hash(key) % _buckets.size();
		Bucket& bucket = _buckets[bucketidx];
		return bucket.get(key);
	}
};

int main() {
	HashTable hashTable;
	hashTable["abc"] = "def";
	hashTable["qwe"] = "qqq";
	hashTable["ewq"] = "eee";

	cout << hashTable["abc"] << endl;
	cout << hashTable["qwe"] << endl;
	cout << hashTable["ewq"] << endl;
}

• 실행 결과

  def
  qqq
  eee