以下是一个使用异步读取接口UA_Client_readValueAttribute_async的简单示例，包括客户端和服务端的实现。
客户端（C++代码）：
#include <open62541/client_config_default.h>
#include <open62541/client_highlevel.h>
int main() {
UA_Client *client = UA_Client_new();
UA_ClientConfig_setDefault(UA_Client_getConfig(client));
// 连接到服务器
UA_StatusCode status = UA_Client_connect(client, "opc.tcp://localhost:4840");
if (status != UA_STATUSCODE_GOOD) {
printf("连接到服务器失败\n");
return status;
}
// 创建异步读取请求
UA_ReadRequest request;
UA_ReadRequest_init(&request);
request.nodesToRead = UA_Array_new(1, &UA_TYPES[UA_TYPES_READVALUEID]);
request.nodesToReadSize = 1;
// 设置要读取的节点信息
request.nodesToRead[0].nodeId = UA_NODEID_NUMERIC(0, 2258); // 修改为实际的节点ID
// 发送异步读取请求
status = UA_Client_Service_readAsync(client, &request);
if (status != UA_STATUSCODE_GOOD) {
printf("发送异步读取请求失败\n");
return status;
}
// 等待响应
UA_Boolean responseReceived = false;
while (!responseReceived) {
status = UA_Client_run_iterate(client, 1000); // 等待响应时间间隔为1秒
if (status == UA_STATUSCODE_BADCONNECTIONCLOSED) {
printf("与服务器的连接已关闭\n");
break;
} else if (status != UA_STATUSCODE_GOOD) {
printf("等待响应时发生错误\n");
break;
}
if (request.response == NULL)
continue;
// 处理读取结果
if (request.response->responseHeader.serviceResult == UA_STATUSCODE_GOOD) {
for (size_t i = 0; i < request.response->resultsSize; ++i) {
UA_DataValue *value = &(request.response->results[i]);
printf("节点值: %f\n", *(UA_Double *)value->value.data);
}
}
responseReceived = true;
}
// 清理资源
UA_ReadRequest_deleteMembers(&request);
UA_Client_disconnect(client);
UA_Client_delete(client);
return 0;
}
服务端（C++代码）：
#include <open62541/server.h>
int main() {
UA_Server *server = UA_Server_new();
UA_ServerConfig_setDefault(UA_Server_getConfig(server));
// 在服务器上创建一个叫做"Temperature"的变量节点，并设置其初始值为25.0
UA_VariableAttributes attr = UA_VariableAttributes_default;
attr.displayName = UA_LOCALIZEDTEXT("en-US", "Temperature");
UA_Double temperature = 25.0;
UA_Variant_setScalarCopy(&attr.value, &temperature, &UA_TYPES[UA_TYPES_DOUBLE]);
UA_NodeId nodeId = UA_NODEID_STRING(1, "Temperature");
UA_QualifiedName browseName = UA_QUALIFIEDNAME(1, "Temperature");
// 将变量节点添加到服务器上
status = UA_Server_addVariableNode(server, nodeId,
parentNodeId, // 修改为实际的父节点ID
referenceTypeId, // 修改为实际的引用类型ID
browseName,
UA_NODEID_NUMERIC(0, UA_NS0ID_BASEDATAVARIABLETYPE),
attr, NULL, NULL);
// 启动服务器
UA_StatusCode status = UA_Server_run(server, &running);
// 关闭服务器
UA_Server_delete(server);
return status;
}
请根据实际情况修改代码中的服务器地址、节点ID等信息。这只是一个简单的示例，实际使用时可能需要进行更多的错误处理和逻辑调整。
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