c++ - thrift 中的 Union 显示在 c++ 中设置的所有值

Question

我做了一个简单的三个字段的并集

union example{
    1:string STRING,
    2:i64 INT64,
    3:double DOUBLE
}

然后我将客户端中的示例 union 实例化为:

example ex;
ex.__set_STRING("Example");
ex.__isset.STRING = true;

并通过接受示例作为参数的方法发送示例

在服务器中，调用的方法是这样完成的:

void get(const example &ex)
  {
    cout << ex.__isset.STRING << ' ' << ex.__isset.INT64 << ' ' <<
        ex.__isset.DOUBLE << endl;
    cout << ex << endl;
  }

奇怪的是，这样一个小程序的输出是:

1 1 1
example(STRING="Example", INT64=0, DOUBLE=0)

我不知道这是否是设置 union 类型的正确方法，但我尝试了几种组合，但似乎都没有用。

片段的来源可以在这里找到:https://github.com/enriquefynn/union_thrift

Answer 1

uint32_t type_ex::write(::apache::thrift::protocol::TProtocol* oprot) const {
  uint32_t xfer = 0;
  apache::thrift::protocol::TOutputRecursionTracker tracker(*oprot);
  xfer += oprot->writeStructBegin("type_ex");

  xfer += oprot->writeFieldBegin("STRING", ::apache::thrift::protocol::T_STRING, 1);
  xfer += oprot->writeString(this->STRING);
  xfer += oprot->writeFieldEnd();

  xfer += oprot->writeFieldBegin("INT64", ::apache::thrift::protocol::T_I64, 2);
  xfer += oprot->writeI64(this->INT64);
  xfer += oprot->writeFieldEnd();

  xfer += oprot->writeFieldBegin("DOUBLE", ::apache::thrift::protocol::T_DOUBLE, 3);
  xfer += oprot->writeDouble(this->DOUBLE);
  xfer += oprot->writeFieldEnd();

  xfer += oprot->writeFieldStop();
  xfer += oprot->writeStructEnd();
  return xfer;
}

看起来像是 union 的错误。这些值是无条件写入的，这适用于 struct 但不适用于 union。因此，解决方法是添加一个显式的 optional:

union type_ex
{
    1 : optional string STRING,
    2 : optional i64 INT64,
    3 : optional double DOUBLE
}

这给了我们:

uint32_t type_ex::write(::apache::thrift::protocol::TProtocol* oprot) const {
  uint32_t xfer = 0;
  apache::thrift::protocol::TOutputRecursionTracker tracker(*oprot);
  xfer += oprot->writeStructBegin("type_ex");

  if (this->__isset.STRING) {
    xfer += oprot->writeFieldBegin("STRING", ::apache::thrift::protocol::T_STRING, 1);
    xfer += oprot->writeString(this->STRING);
    xfer += oprot->writeFieldEnd();
  }
  if (this->__isset.INT64) {
    xfer += oprot->writeFieldBegin("INT64", ::apache::thrift::protocol::T_I64, 2);
    xfer += oprot->writeI64(this->INT64);
    xfer += oprot->writeFieldEnd();
  }
  if (this->__isset.DOUBLE) {
    xfer += oprot->writeFieldBegin("DOUBLE", ::apache::thrift::protocol::T_DOUBLE, 3);
    xfer += oprot->writeDouble(this->DOUBLE);
    xfer += oprot->writeFieldEnd();
  }
  xfer += oprot->writeFieldStop();
  xfer += oprot->writeStructEnd();
  return xfer;
}

Bug report filed .