FlatBuffers學習筆記一——初識FlatBuffers

一、文件下載

1.下載flatc.exe工具和FlatBuffers源碼，鏈接請點我； 
2.用Visual Studio打開源碼/net/FlatBuffers/FlatBuffers.csproj項目，編譯輸出類庫文件FlatBuffers.dll； 
3.查看官方說明文檔請點我； 
4.官方C#示例代碼可見源碼/tests/FlatBuffers.Test工程

 

二、工具介紹

1.flatc.exe

   此文件是根據fbs文件生成解析數據的代碼文件，如果是C#的話，那麼就生成cs代碼文件;

2.fbs文件

   此文件用於定義數據文件的文件格式，類似mysql數據庫中的表結構，不包括表數據;

3.FlatBuffers.dll

   flac.exe生成的代碼文件通過該文件來解析數據;

 

三、開始使用

1.編寫fbs文件

   例如文件名: MyGame.fbs

// Example IDL file for our monster's schema.
namespace MyGame.Sample;

enum Color:byte { Red = 0, Green, Blue = 2 }

union Equipment { Weapon } 

// Optionally add more tables.
struct Vec3 {
  x:float;
  y:float;
  z:float;
}

table Monster {
  pos:Vec3; // Struct.
  mana:short = 150;
  hp:short = 100;
  name:string;
  friendly:bool = false (deprecated);
  inventory:[ubyte];  // Vector of scalars.
  color:Color = Blue; // Enum.
  weapons:[Weapon];   // Vector of tables.
  equipped:Equipment; // Union.
}

table Weapon {
  name:string;
  damage:short;
}

root_type Monster;

2.生成代碼文件

   這裏我們只生成C#代碼文件, 可以在CMD工具欄中通過命令行生成，也可以使用下面的代碼生成：

D:\Projects\FlatBuffers\Test\flatc.exe -n -o MyGame.fbs --gen-onefile
@pause

   將上面的兩行代碼保存到compile.bat文件中，然後雙擊compile.bat文件看看有什麼結果。

3.flatc參數的含義

   我們可以通過flatc.exe /?命令來查看參數的含義，如下：

D:\Projects\FlatBuffers\Test>flatc.exe /?
flatc.exe: error: no options: specify at least one generator.
Usage: flatc.exe [OPTION]... FILE... [-- FILE...]
  --binary     -b    Generate wire format binaries for any data definitions.
  --json       -t    Generate text output for any data definitions.
  --cpp        -c    Generate C++ headers for tables/structs.
  --go         -g    Generate Go files for tables/structs.
  --java       -j    Generate Java classes for tables/structs.
  --js         -s    Generate JavaScript code for tables/structs.
  --dart       -d    Generate Dart classes for tables/structs.
  --ts         -T    Generate TypeScript code for tables/structs.
  --csharp     -n    Generate C# classes for tables/structs.
  --python     -p    Generate Python files for tables/structs.
  --lobster          Generate Lobster files for tables/structs.
  --lua        -l    Generate Lua files for tables/structs.
  --rust       -r    Generate Rust files for tables/structs.
  --php              Generate PHP files for tables/structs.
  --jsonschema       Generate Json schema.
  -o PATH            Prefix PATH to all generated files.
  -I PATH            Search for includes in the specified path.
  -M                 Print make rules for generated files.
  --version          Print the version number of flatc and exit.
  --strict-json      Strict JSON: field names must be / will be quoted,
                     no trailing commas in tables/vectors.
  --allow-non-utf8   Pass non-UTF-8 input through parser and emit nonstandard
                     \x escapes in JSON. (Default is to raise parse error on
                     non-UTF-8 input.)
  --natural-utf8     Output strings with UTF-8 as human-readable strings.
                     By default, UTF-8 characters are printed as \uXXXX escapes.
  --defaults-json    Output fields whose value is the default when
                     writing JSON
  --unknown-json     Allow fields in JSON that are not defined in the
                     schema. These fields will be discared when generating
                     binaries.
  --no-prefix        Don't prefix enum values with the enum type in C++.
  --scoped-enums     Use C++11 style scoped and strongly typed enums.
                     also implies --no-prefix.
  --gen-includes     (deprecated), this is the default behavior.
                     If the original behavior is required (no include
                     statements) use --no-includes.
  --no-includes      Don't generate include statements for included
                     schemas the generated file depends on (C++).
  --gen-mutable      Generate accessors that can mutate buffers in-place.
  --gen-onefile      Generate single output file for C# and Go.
  --gen-name-strings Generate type name functions for C++.
  --gen-object-api   Generate an additional object-based API.
  --gen-compare      Generate operator== for object-based API types.
  --cpp-ptr-type T   Set object API pointer type (default std::unique_ptr)
  --cpp-str-type T   Set object API string type (default std::string)
                     T::c_str() and T::length() must be supported
  --gen-nullable     Add Clang _Nullable for C++ pointer. or @Nullable for Java
  --object-prefix    Customise class prefix for C++ object-based API.
  --object-suffix    Customise class suffix for C++ object-based API.
                     Default value is "T"
  --no-js-exports    Removes Node.js style export lines in JS.
  --goog-js-export   Uses goog.exports* for closure compiler exporting in JS.
  --es6-js-export    Uses ECMAScript 6 export style lines in JS.
  --go-namespace     Generate the overrided namespace in Golang.
  --go-import        Generate the overrided import for flatbuffers in Golang.
                     (default is "github.com/google/flatbuffers/go")
  --raw-binary       Allow binaries without file_indentifier to be read.
                     This may crash flatc given a mismatched schema.
  --size-prefixed    Input binaries are size prefixed buffers.
  --proto            Input is a .proto, translate to .fbs.
  --oneof-union      Translate .proto oneofs to flatbuffer unions.
  --grpc             Generate GRPC interfaces for the specified languages
  --schema           Serialize schemas instead of JSON (use with -b)
  --bfbs-comments    Add doc comments to the binary schema files.
  --bfbs-builtins    Add builtin attributes to the binary schema files.
  --conform FILE     Specify a schema the following schemas should be
                     an evolution of. Gives errors if not.
  --conform-includes Include path for the schema given with --conform
    PATH
  --include-prefix   Prefix this path to any generated include statements.
    PATH
  --keep-prefix      Keep original prefix of schema include statement.
  --no-fb-import     Don't include flatbuffers import statement for TypeScript.
  --no-ts-reexport   Don't re-export imported dependencies for TypeScript.
  --reflect-types    Add minimal type reflection to code generation.
  --reflect-names    Add minimal type/name reflection.
  --root-type T      Select or override the default root_type
  --force-defaults   Emit default values in binary output from JSON
  --force-empty      When serializing from object API representation,                      force strings and vectors to empty rather than null.
FILEs may be schemas (must end in .fbs), or JSON files (conforming to preceding
schema). FILEs after the -- must be binary flatbuffer format files.
Output files are named using the base file name of the input,
and written to the current directory or the path given by -o.
example: flatc.exe -c -b schema1.fbs schema2.fbs data.json

通過參數說明我們知道:

-n   表示生成C#代碼

--gen-onefile 表示將文件中的多個結構體生成到一個代碼文件中，如果不加這個參數，那麼有幾個結構體就會生成幾個代碼文件.

 

至此我們就把flatc.exe的用法搞明白了，最終我們是希望解析數據文件，那麼第二講我會講解如何使用生成的代碼文件來解析數據，然後就會用到FlatBuffers.dll了。