c ++使用平面缓冲区在二进制文件中写入具有循环依赖性的数据

Question

我正在尝试使用平面缓冲区将图形写入二进制文件。图由节点和边组成。每个节点至少有一条边，每条边由两个节点组成。

摘自MyGraph.fbs：

namespace MyGraph;

table Node {
  edges:[Edge];
}

table Edge {
  startNode:Node;
  endNode:Node;
}

table Graph {
  allNodes:[Node];
}

root_type Graph;

现在我想创建一个简单的图形并将其写入字节文件:

FlatBufferBuilder fbb;
// create first node
auto node1mloc = DG::CreateNode(fbb, 0, 0);

// create second node
auto node2mloc = DG::CreateNode(fbb, 0, 0);

// create edge between first and second node
auto edgeloc = DG::CreateEdge(fbb, node1mloc, node2mloc);


// ???
// store the edge in the edges-vector of node1 and node2
// ???

// store nodes in graph
flatbuffers::Offset<Node> nodes[] = {node1mloc, node2mloc};

auto allNodes = fbb.CreateVector(nodes, 2);

auto graphloc = DG::CreateGraph(fbb, allNodes);

DG::FinishGraphBuffer(fbb, graphloc);


// write graph into file
auto buffer_pointer = fbb.GetBufferPointer();
SaveFile("myfile2.bin", reinterpret_cast<const char *>(buffer_pointer), fbb.GetSize(), true);



// load graph from file
string binData;
LoadFile("myfile2.bin", true, &binData);

auto graph = DG::GetGraph(binData.data());
cout << graph->allNodes()->size() << endl;
assert(graph->allNodes()->size() == 2);

问题是，在创建节点后，我无法将边添加到节点 1 和节点 2 的边向量中。有没有办法解决两种类型之间的那种循环依赖。

Answer 1

您不能在 FlatBuffer 中存储循环结构（它使用无符号偏移量强制子项总是在父项之前）。

但是，您可以存储 DAG。

要对循环结构进行编码，您必须对节点或边引用使用索引，例如

table Edge {
  startNode:uint;
  endNode:uint;
}

这意味着这些节点引用是 allNodes.

的索引

请注意，只有极少数序列化格式允许使用图表，例如Protocol Buffers 和 JSON 都只允许树。

Answer 2

这在 FlatBuffersSwift 中有效，但在官方 FlatBuffers 实现中不受支持。

//: Playground - noun: a place where people can play

import Foundation

var str = "Hello, playground"


let (f1, f2, f3, f4) = (Friend(), Friend(), Friend(), Friend())

f1.name = "Maxim"
f2.name = "Leo"
f3.name = "Boris"
f4.name = "Marc"

let f5 = Friend()
f5.name = "Daria"

f1.friends = [f1, f2, f3, f4]
f2.friends = [f1, f4]
f3.friends = [f2, f4]

f1.lover = Female(ref: f5)
f5.lover = Male(ref: f1)

f1.father = Friend()
f1.father?.name = "Issai"

f1.mother = Friend()
f1.mother?.name = "Margo"

let data = f1.toByteArray()

let f = Friend.fromByteArray(UnsafeBufferPointer(start:UnsafePointer<UInt8>(data), count: data.count))

print(f.friends[2]?.friends[0]?.friends[0]?.name)

print(((f.lover as? Female)?.ref?.lover as? Male)?.ref?.name)


let lazyF = Friend.Fast(data)

let girlFriend = (lazyF.lover as! Female.Fast).ref
let boyFriend = (girlFriend?.lover as! Male.Fast).ref

lazyF == boyFriend

我在 google 群聊中询问是否对主要项目感兴趣。看来这不会很快发生。

https://groups.google.com/forum/#!topic/flatbuffers/Y9K9wRKSHxg

c ++使用平面缓冲区在二进制文件中写入具有循环依赖性的数据

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