c++使用proto3的map

Introduction:

自proto3开始, proto2和proto3就可以支持map. ##官方文档中有如下声明:##

Added support for map fields (implemented in both proto2 and proto3). Map fields can be declared using the following syntax:

>message Foo { map<string, string> values = 1; }

The data of a map field is stored in memory as an unordered map and can be accessed through generated accessors.

proto3 map源码:

template<typename Key, typename T> { class Map { // Member types typedef Key key_type; typedef T mapped_type; typedef MapPair< Key, T > value_type; // Iterators iterator begin(); const_iterator begin() const; const_iterator cbegin() const; iterator end(); const_iterator end() const; const_iterator cend() const; // Capacity int size() const; bool empty() const; // Element access T& operator[](const Key& key); const T& at(const Key& key) const; T& at(const Key& key); // Lookup int count(const Key& key) const; const_iterator find(const Key& key) const; iterator find(const Key& key); // Modifiers pair<iterator, bool> insert(const value_type& value); template<class InputIt> void insert(InputIt first, InputIt last); size_type erase(const Key& Key); iterator erase(const_iterator pos); iterator erase(const_iterator first, const_iterator last); void clear(); // Copy Map(const Map& other); Map& operator=(const Map& other); }

map的赋值方式:

1.简单的赋值方式:

The easiest way to add data is to use normal map syntax, for example:

最简单的赋值方式就是用C++的普通Map语法, 如下第二行:

std::unique_ptr<ProtoName> my_enclosing_proto(new ProtoName); (*my_enclosing_proto->mutable_weight())[my_key] = my_value;

2.有效的赋值方式:

pair<iterator, bool> insert(const value_type& value) will implicitly cause a deep copy of the value_type instance. The most efficient way to insert a new value into a google::protobuf::Map is as follows:

pair<iterator, bool> insert(const value_type& value)会隐式地调用value_type实例的深拷贝, 最有效的插入新值方式是:

T& operator[](const Key& key): map[new_key] = new_mapped;

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std::map与google::protobuf::Map的相互转换:

google::protobuf::Map转换成std::map:

Using google::protobuf::Map with standard maps google::protobuf::Map supports the same iterator API as std::map and std::unordered_map. If you don’t want to use google::protobuf::Map directly, you can convert a google::protobuf::Map to a standard map by doing the following:

google::protobuf::Map 支持std::map和std::unordered_map的API, 如果你不想直接使用google::protobuf::Map, 可以如下方式将google::protobuf::Map转换成标准库的Map

std::map<int32, int32> standard_map(message.weight().begin(), message.weight().end());

Note that this will make a deep copy of the entire map.

注意:这会深拷贝整个Map

std::map转换成google::protobuf::Map:

You can also construct a google::protobuf::Map from a standard map as follows:

当然, 你也可以通过标准库中的Map构造一个google::protobuf::Map, 如下所示:

google::protobuf::Map<int32, int32> weight(standard_map.begin(), standard_map.end());