90 lines
2.6 KiB
Markdown
90 lines
2.6 KiB
Markdown
##### flatc
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```bash
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# 编译flatc
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git clone https://github.com/google/flatbuffers.git
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export CC=/usr/bin/clang
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export CXX=/usr/bin/clang++
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cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release -B build
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cd build && make
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# 用法
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flatc [options] <files> [-- files]
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--cpp, -c # 生成C++头文件
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--python, -p # 生成Python文件
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--gen-mutable # 生成可以改变缓冲区的访问器。(缓冲区默认是不可改变的)
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```
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##### schema语言
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`namespace <NameSpace>;`定义命名空间NameSpace。
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`enum <name>:<type> {}`定义枚举类型。
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`union <name> {}`定义联合类型。
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`struct <name> {}`定义结构体。
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`table <name> {}`定义列表。列表里的字段不可删除，但可以使用`deprecated`来阻止生成代码访问这个字段。
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`root_type`用来声明序列化数据的根列表。
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详见如下文档：
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- [writing a schema](https://google.github.io/flatbuffers/flatbuffers_guide_writing_schema.html)
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- [grammar of the schema language](https://google.github.io/flatbuffers/flatbuffers_grammar.html)
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##### 用C++读写FlatBuffers
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```cpp
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// #include生成的文件并using namespace
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// 使用FlatBufferBuilder实例化一个缓冲区
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// 在序列化一个对象前，先要序列化其中包含的任何对象
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// 最后，调用finish方法结束序列化。
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// 保存缓冲区，注意要保存为二进制格式。
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// 使用g++或clang++编译器
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/* 把buffer写入文件示例代码 */
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std::ofstream outfile;
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outfile.open("csample.bat", std::ios::binary | std::ios::out);
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outfile.write((const char *)builder.GetBufferPointer(), builder.GetSize());
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outfile.close();
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/* 从文件读入buffer示例代码 */
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std::ifstream infile;
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infile.open("csample.bat", std::ios::binary | std::ios::in);
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infile.seekg(0, std::ios::end);
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int length = infile.tellg();
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infile.seekg(0, std::ios::beg);
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char *data = new char[length];
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infile.read(data, length);
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infile.close();
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```
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详见如下文档：
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- [tutorial](https://google.github.io/flatbuffers/flatbuffers_guide_tutorial.html)
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- [use cpp](https://google.github.io/flatbuffers/flatbuffers_guide_use_cpp.html)
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- [api](https://google.github.io/flatbuffers/group__flatbuffers__cpp__api.html)
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##### 用Python读写FlatBuffers
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```python
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# 把buffer写入文件示例代码
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file = open('psample.bat','wb');
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file.write(builder.Output());
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file.close;
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# 从文件读入buffer示例代码
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file = open('psample.bat','rb');
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buf = file.read();
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buf = bytearray(buf);
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file.close;
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```
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详见如下文档：
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- [use python](https://google.github.io/flatbuffers/flatbuffers_guide_use_python.html)
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