map
Prerequisites:
map介紹
include
#include <map>
map的值是pair
map是以紅黑樹(AVL tree)排序，所以把map的值印出來會是以排序好的方式印出。
初始化
語法
map(initializer_list<pair<K,V>> il);
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// 建立空的map
map<int, string> m1;
// 使用initializer初始化值
// map(initializer_list<pair<K,V>>)
map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
// 省略等於號寫法
// map<int,string> m2 { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
// 使用括號
// map<int,string> m2({ {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} });
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
6,Ken 7,Alice 8,Juli 9,Bill 10,Mary
使用[]印出元素
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map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
cout << "m2[10] = " << m2[10] << endl;
m2[10] = Mary
若key不存在map中，則會新增空值
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map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
cout << "m2[10] = " << m2[10] << endl;
cout << "m2[22] = " << m2[22] << endl;
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
m2[10] = Mary
m2[22] =
6,Ken 7,Alice 8,Juli 9,Bill 10,Mary 22,
新增修改
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map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
cout << "修改前" << endl;
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
// 新增
m2[5] = "Eva";
m2[4] = "Iric";
// 修改
m2[10] = "Yoyo";
m2[9] = "Momo";
cout << "修改後" << endl;
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
修改前
6,Ken 7,Alice 8,Juli 9,Bill 10,Mary
修改後
4,Iric 5,Eva 6,Ken 7,Alice 8,Juli 9,Momo 10,Yoyo
插入insert
傳回值為void
語法
void insert(initializer_list<pair<K,V>> il);
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map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
cout << "修改前" << endl;
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
m2.insert({ {1, "Ben"}, {2, "Cindy"}, {3, "Rita"} });
cout << "插入後" << endl;
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
修改前
6,Ken 7,Alice 8,Juli 9,Bill 10,Mary
插入後
1,Ben 2,Cindy 3,Rita 6,Ken 7,Alice 8,Juli 9,Bill 10,Mary
若插入的key已存在map中，則不會插入，也不會提示錯誤
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map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
cout << "修改前" << endl;
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
m2.insert({ {10, "Ben"}, {9, "Cindy"}, {3, "Rita"} });
cout << "插入後" << endl;
for (auto& val:m2) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
修改前
6,Ken 7,Alice 8,Juli 9,Bill 10,Mary
插入後
3,Rita 6,Ken 7,Alice 8,Juli 9,Bill 10,Mary
傳回值為pair
語法
pair<iterator,bool> insert(initializer_list<pair<K,V>> il);
傳回值pair:first已插入的元素的iterator，second是插入的結果
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map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
auto ret = m2.insert({5, "Julia"});
if (ret.second == true) {
cout << "成功" << ", first = " << ret.first->first
<< ", second = " << ret.first -> second << endl;
} else {
cout << "失敗" << endl;
}
成功, first = 5, second = Julia
使用emplace
pair<iterator,bool> emplace(initializer_list<pair<K,V>> il);
傳回值跟先前的一樣，不同的是使用emplace可以原地建構。
使用iterator建立map
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map<int,string> m2 = { {10, "Mary"}, {9, "Bill"}, {7, "Alice"}, {8, "Juli"}, {6, "Ken"} };
m2.insert({ {1, "Ben"}, {2, "Cindy"}, {3, "Rita"} });
// 使用iterator建立map
auto first = m2.begin();
first++;
auto last = m2.end();
last--;
map<int, string> m3(first, last);
for (auto & val:m3) {
cout << val.first << "," << val.second << " ";
}
cout << endl;
2,Cindy 3,Rita 6,Ken 7,Alice 8,Juli 9,Bill