Implementation:Alibaba MNN FlexBuffers Header

Knowledge Sources	Alibaba_MNN FlatBuffers
Domains	Serialization, Dynamic_Data
Last Updated	2026-02-10 12:00 GMT

Overview

Schema-less variant of FlatBuffers that supports self-describing, dynamically-typed binary data.

Description

flexbuffers.h implements the FlexBuffers format, a schema-less companion to FlatBuffers. It provides flexbuffers::Builder for constructing dynamically-typed data and flexbuffers::Reference for reading it back without a schema. This is useful for storing heterogeneous metadata and configuration data within MNN models where a fixed schema is impractical.

Usage

Vendored dependency used internally by MNN for model serialization. Not directly imported by end users.

Code Reference

Source Location

• Repository: Alibaba_MNN
• File: 3rd_party/flatbuffers/include/flatbuffers/flexbuffers.h
• Lines: 1-1538

Signature

namespace flexbuffers {
  class Builder;
  class Reference;
  class Map;
  class Vector;
  Reference GetRoot(const uint8_t *buffer, size_t size);
}

Import

#include "flatbuffers/flexbuffers.h"

I/O Contract

Input	Output
Dynamic key-value data via Builder API	Self-describing binary FlexBuffer
Raw FlexBuffer bytes	Typed accessors via Reference, Map, Vector

Usage Examples

#include "flatbuffers/flexbuffers.h"

flexbuffers::Builder fbb;
fbb.Map([&]() {
    fbb.String("name", "relu");
    fbb.Int("version", 3);
});
fbb.Finish();

auto ref = flexbuffers::GetRoot(fbb.GetBuffer());
std::string name = ref.AsMap()["name"].AsString().str();
int version = ref.AsMap()["version"].AsInt32();

Related Pages

• Environment:Alibaba_MNN_CPU_Build_Environment