跳到主要内容

Read / Write

前置阅读

Read​

DataValue Read(std::string const& node_id,
               AttributeId attr = AttributeId::Value);

读单节点的指定 Attribute.

参数类型默认说明
node_idstd::string const&—NodeId 字符串 (i=2258 / ns=2;s=...)
attrAttributeIdValue (13)要读的属性

返回: DataValue (栈对象, 析构自动释放)

异常: Exception (BadNodeIdUnknown / BadNotReadable / BadCommunicationError / ...)

// 读 Value
auto dv = s.Read("ns=2;s=Temperature");
double t = 0; dv.Value().TryGetDouble(t);
std::cout << t << "\n";

// 读 DisplayName
auto dn = s.Read("ns=2;s=Temperature", AttributeId::DisplayName);
std::cout << dn.Value().AsString() << "\n";

ReadMany​

std::vector<DataValue> ReadMany(
    std::vector<std::string> const& node_ids,
    AttributeId attr = AttributeId::Value);

一次 RPC 批量读多个节点的同一 Attribute.

std::vector<std::string> nodes = { "ns=2;s=T1", "ns=2;s=T2", "ns=2;s=T3" };
auto values = s.ReadMany(nodes);
for (size_t i = 0; i < nodes.size(); ++i) {
    std::cout << nodes[i] << " = " << values[i].Value().AsString() << "\n";
}

性能: 批量比循环单读快 ~N 倍 (省 N-1 次 RPC 往返).

如果某个节点解析失败, 对应槽位 Handle() 为空, 用前先检查.

Write​

Status Write(std::string const& node_id,
             Variant const& value,
             AttributeId attr = AttributeId::Value);

写单节点.

Variant v; v.SetDouble(42.5);
Status st = s.Write("ns=2;s=Setpoint", v);
if (st != Status::Good) {
    std::cerr << "Write failed: 0x" << std::hex << static_cast<uint32_t>(st) << "\n";
}

返回 Status (Good / BadNotWritable / BadTypeMismatch / BadUserAccessDenied / ...).

业务级失败不抛异常

Write 不抛异常 (除非 transport 级错误), 业务级失败通过返回值判断. 必须检查返回值, 不要假定 Good.

Variant 构造速查​

Variant v;
v.SetBool(true);                  // Boolean
v.SetInt16(42);                   // Int16
v.SetInt32(42);                   // Int32
v.SetInt64(42LL);                 // Int64
v.SetDouble(3.14);                // Double
v.SetFloat(3.14f);                // Float
v.SetString("hello");             // String
v.SetDateTime(file_time);         // DateTime (FileTime: 100ns since 1601)

详见 Variant 数据类型.

DataValue 字段速查​

访问器类型说明
Value()Variant实际值 (借用)
StatusCode()uint32_t原始 32-bit 状态码
StatusEnum()Status强类型枚举
IsGood()bool等价 StatusCode() == 0
SourceTimestamp()int64_tFileTime (100ns since 1601)
ServerTimestamp()int64_tFileTime
auto dv = s.Read("ns=2;s=T1");
if (!dv.IsGood()) {
    std::cerr << "Bad value: 0x" << std::hex << dv.StatusCode() << "\n";
    return;
}
double t = 0; dv.Value().TryGetDouble(t);
std::cout << t << " @ ft=" << dv.SourceTimestamp() << "\n";

AttributeId 常用值​

enum class AttributeId : int {
    NodeId = 1, NodeClass = 2, BrowseName = 3, DisplayName = 4,
    Description = 5, WriteMask = 6, UserWriteMask = 7,
    IsAbstract = 8, Symmetric = 9, InverseName = 10,
    ContainsNoLoops = 11, EventNotifier = 12,
    Value = 13,             // 默认
    DataType = 14, ValueRank = 15, ArrayDimensions = 16,
    AccessLevel = 17, UserAccessLevel = 18,
    MinimumSamplingInterval = 19, Historizing = 20,
    Executable = 21, UserExecutable = 22,
};

最佳实践​

  • 批量优先: 监控 100+ Tag 用 ReadMany, 不要循环 Read
  • 栈对象 RAII: auto dv = s.Read(...); 离开作用域自动释放, 不要 new
  • Write 检查返回值: 不要假定一定 Good
  • 实时变化用订阅: 不要循环 Read, 改用 Subscription (服务端推送)

下一步​