how to store multiple values under same key using hashing in c++

Question

我想使用散列技术在c ++中创建电话目录项目。我需要做的一件事是它必须基于location搜索联系人，因此我将位置作为键值，但同一位置将有多个联系人。所以如何在同一键（位置）下存储多个值（名称，电话号码）。

Answer 1

If you are using C++11 or newer, you could use std::unordered_multimap to store multiple entries per key (eg multiple entries per location). It is a hash map that allows multiple entries with the same key. To store multiple properties per entry, you can use a struct or class. Finally, it could look like this:

struct contact_t {
    std::string name;
    std::string phone_number;
}

std::unordered_multimap<std::string, contact_t> directory;

int main(int argc, char *argv[])
{
    // Add entry
    contact_t contact;
    contact.name = "Fooman";
    contact.phone_number = "00 000 00000000";
    directory.emplace("Barcity", contact);

    // List all entries of one city
    auto range = directory.equal_range("Barcity");
    for (auto it = range.first; it != range.second; ++it) {
        auto &entry = it->second; // it->first would be the key/location
        std::cout << "Name: " << entry.name
                  << "Phone: " << entry.phone_number << std::endl;
    }
}

However, consider that values with the same key are not sorted. You may want to use something like std::unordered_map<std::string, std::multiset<contact_t>> instead.