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101 lines (93 loc) · 2.85 KB
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//
// Created by william on 2021/8/8.
//
#include "base.h"
struct Key
{
std::string first;
std::string second;
};
struct KeyHash
{
std::size_t operator()(const Key& k) const
{
return std::hash<std::string>()(k.first) ^ (std::hash<std::string>()(k.second)) << 1;
}
};
struct KeyEqual
{
bool operator()(const Key& lhs, const Key& rhs) const
{
return lhs.first == rhs.first && lhs.second == rhs.second;
}
};
struct Foo
{
Foo(int val_) :
val(val_) {}
int val;
bool operator==(const Foo& rhs) const { return val == rhs.val; }
};
namespace std
{
template <>
struct hash<Foo>
{
std::size_t operator()(const Foo& f) const
{
return std::hash<int>{}(f.val);
}
};
} // namespace std
void unorderedMapTest()
{
// 创建三个 string 的 unordered_map （映射到 string ）
std::unordered_map<std::string, std::string> u = {
{ "RED", "#FF0000" },
{ "GREEN", "#00FF00" },
{ "BLUE", "#0000FF" }
};
// 迭代并打印 unordered_map 的关键和值
for (const auto& n : u)
{
std::cout << "Key:[" << n.first << "] Value:[" << n.second << "]\n";
}
// 添加新入口到 unordered_map
u["BLACK"] = "#000000";
u["WHITE"] = "#FFFFFF";
// 用关键输出值
std::cout << "The HEX of color RED is:[" << u["RED"] << "]\n";
std::cout << "The HEX of color BLACK is:[" << u["BLACK"] << "]\n";
// 默认构造函数：空 unordered_map
std::unordered_map<std::string, std::string> m1;
// 列表构造函数
std::unordered_map<int, std::string> m2 = {
{ 1, "foo" },
{ 3, "bar" },
{ 2, "baz" },
};
// 复制构造函数
std::unordered_map<int, std::string> m3 = m2;
// 移动构造函数
std::unordered_map<int, std::string> m4 = std::move(m2);
// 范围构造函数
std::vector<std::pair<std::bitset<8>, int>> v = { {0x12, 1}, {0x01,-1} };
std::unordered_map<std::bitset<8>, double> m5(v.begin(), v.end());
// 带定制 Key 类型的构造函数的选项 1
// 定义 KeyHash 与 KeyEqual 结构体并在模板中使用它们
std::unordered_map<Key, std::string, KeyHash, KeyEqual> m6 = {
{ {"John", "Doe"}, "example"},
{ {"Mary", "Sue"}, "another"}
};
// 带定制 Key 类型的构造函数的选项 2
// 为 class/struct 定义 const == 运算符并于 std 命名空间特化 std::hash 结构体
std::unordered_map<Foo, std::string> m7 = {
{ Foo(1), "One"}, { 2, "Two"}, { 3, "Three"}
};
// 选项 3 ：用 lambdas
// 注意必须将初始桶数传递给构造函数
struct Goo {int val; };
auto hash = [](const Goo &g){ return std::hash<int>{}(g.val); };
auto comp = [](const Goo &l, const Goo &r){ return l.val == r.val; };
std::unordered_map<Goo, double, decltype(hash), decltype(comp)> m8(10, hash, comp);
}