我正在尝试使用C++中的Flatbuffers,但是我已经无法在联合中编写和读取结构。我已将最初的问题简化为一个匿名的最小示例。
示例架构(favorite.fbs
)
// favorite.fbs
struct FavoriteNumbers
{
first: uint8;
second: uint8;
third: uint8;
}
union Favorite
{ FavoriteNumbers }
table Data
{ favorite: Favorite; }
root_type Data;
我使用从release page下载的Flatbuffers 1.11.0编译了模式(我在Windows上,为了安全起见,我使用了预编译的二进制文件)。
flatc --cpp favorite.fbs
这将生成文件
favorite_generated.h
。示例代码(
fav.cpp
)#include <iostream>
#include "favorite_generated.h"
int main(int, char**)
{
using namespace flatbuffers;
FlatBufferBuilder builder;
// prepare favorite numbers and write them to the buffer
FavoriteNumbers inFavNums(17, 42, 7);
auto inFav{builder.CreateStruct(&inFavNums)};
auto inData{CreateData(builder, Favorite_FavoriteNumbers, inFav.Union())};
builder.Finish(inData);
// output original numbers from struct used to write (just to be safe)
std::cout << "favorite numbers written: "
<< +inFavNums.first() << ", "
<< +inFavNums.second() << ", "
<< +inFavNums.third() << std::endl;
// output final buffer size
std::cout << builder.GetSize() << " B written" << std::endl;
// read from the buffer just created
auto outData{GetData(builder.GetBufferPointer())};
auto outFavNums{outData->favorite_as_FavoriteNumbers()};
// output read numbers
std::cout << "favorite numbers read: "
<< +outFavNums->first() << ", "
<< +outFavNums->second() << ", "
<< +outFavNums->third() << std::endl;
return 0;
}
我正在使用一元
+
到force numerical output instead of characters。 An answer to another question here on StackOverflow告诉我我必须使用CreateStruct
才能实现所需的功能。我使用M ++ 2的g++ 9.1.0编译了代码。g++ -std=c++17 -Ilib/flatbuffers/include fav.cpp -o main.exe
这将生成文件
main.exe
。输出量
favorite numbers written: 17, 42, 7
32 B written
favorite numbers read: 189, 253, 34
显然,这不是理想的结果。我究竟做错了什么?
最佳答案
删除&
前面的inFavNums
,它将起作用。CreateStruct
是一个模板函数,在这种情况下,很遗憾,这意味着它也将使用指针而不抱怨它。避免这种情况很好,但是在C++中并不是那么容易。