问题

I've been working for a long time with Python and the FreeOPCUA Stack, but I wanted to go into more low-level stuff, so I wanted to try the Open62541 Stack. My C skills are a bit rusted, but I understand the concepts and syntax.

我已经用Python和FreeOPCUA Stack工作了很长时间，但我想深入研究更底层的东西，所以我想尝试Open62541 Stack。我的C技能有点生疏，但我理解概念和语法。

I am trying to create a method node without an input argument. Once called, the method should call a function and return as output the function's output. In Python, the arguments are passed into the add_method as a list. In C, it should be a string or an array of strings.

我正在尝试创建一个没有输入参数的方法节点。一旦调用，该方法应该调用一个函数，并将函数的输出作为输出返回。在Python中，参数被传递到add_method作为一个列表。在C中，它应该是一个字符串或字符串数组。

How should I write it in order to have just a function call, without inputs?

我应该如何编写它，以便只进行函数调用，没有输入参数？

I was following the docs at https://www.open62541.org/doc/1.0/tutorial_server_method.html, but the two examples take input arguments (even the hello world), and since then I am stuck.

我曾经按照https://www.open62541.org/doc/1.0/tutorial_server_method.html上的文档，但两个示例都使用了输入参数（甚至是hello world），从那以后我就卡住了。

答案1

得分: 1

以下是您提供的代码的中文翻译：

我实际上在做一些愚蠢的事情，编译错误。输入参数大小可以设置为零，并且可以将输入参数的引用设置为NULL。

我的方法定义如下：

static UA_StatusCode
enableRobotMethodCallback(UA_Server *server,
                         const UA_NodeId *sessionId, void *sessionHandle,
                         const UA_NodeId *methodId, void *methodContext,
                         const UA_NodeId *objectId, void *objectContext,
                         size_t inputSize, const UA_Variant *input,
                         size_t outputSize, UA_Variant *output) {
    UA_String tmp = UA_STRING_ALLOC(enableRobot());
    UA_Variant_setScalarCopy(output, &tmp, &UA_TYPES[UA_TYPES_STRING]);
    UA_String_clear(&tmp);
    return UA_STATUSCODE_GOOD;
}

static void
addEnableRobotMethod(UA_Server *server) {
    UA_Argument outputArgument;
    UA_Argument_init(&outputArgument);
    outputArgument.description = UA_LOCALIZEDTEXT("en-US", "一个字符串");
    outputArgument.name = UA_STRING("MyOutput");
    outputArgument.dataType = UA_TYPES[UA_TYPES_STRING].typeId;
    outputArgument.valueRank = UA_VALUERANK_SCALAR;

    UA_MethodAttributes enableRobot = UA_MethodAttributes_default;
    enableRobot.description = UA_LOCALIZEDTEXT("en-US", "启用机器人");
    enableRobot.displayName = UA_LOCALIZEDTEXT("en-US", "启用机器人");
    enableRobot.executable = true;
    enableRobot.userExecutable = true;
    UA_Server_addMethodNode(server, UA_NODEID_NUMERIC(1,20),
                            UA_NODEID_NUMERIC(0, UA_NS0ID_OBJECTSFOLDER),
                            UA_NODEID_NUMERIC(0, UA_NS0ID_HASCOMPONENT),
                            UA_QUALIFIEDNAME(1, "启用机器人"),
                            enableRobot, &enableRobotMethodCallback,
                            0, NULL, 1, &outputArgument, NULL, NULL);
}

请注意，我已将代码中的HTML实体（如&和"）还原为其原始形式，以便更清晰地阅读代码。

static UA_StatusCode
enableRobotMethodCallback(UA_Server *server,
                         const UA_NodeId *sessionId, void *sessionHandle,
                         const UA_NodeId *methodId, void *methodContext,
                         const UA_NodeId *objectId, void *objectContext,
                         size_t inputSize, const UA_Variant *input,
                         size_t outputSize, UA_Variant *output) {
    UA_String tmp = UA_STRING_ALLOC(enableRobot());
    UA_Variant_setScalarCopy(output, &tmp, &UA_TYPES[UA_TYPES_STRING]);
    UA_String_clear(&tmp);
    return UA_STATUSCODE_GOOD;
}

static void
addEnableRobotMethod(UA_Server *server) {
    UA_Argument outputArgument;
    UA_Argument_init(&outputArgument);
    outputArgument.description = UA_LOCALIZEDTEXT("en-US", "A String");
    outputArgument.name = UA_STRING("MyOutput");
    outputArgument.dataType = UA_TYPES[UA_TYPES_STRING].typeId;
    outputArgument.valueRank = UA_VALUERANK_SCALAR;

    UA_MethodAttributes enableRobot = UA_MethodAttributes_default;
    enableRobot.description = UA_LOCALIZEDTEXT("en-US","Enable Robot");
    enableRobot.displayName = UA_LOCALIZEDTEXT("en-US","Enable Robot");
    enableRobot.executable = true;
    enableRobot.userExecutable = true;
    UA_Server_addMethodNode(server, UA_NODEID_NUMERIC(1,20),
                            UA_NODEID_NUMERIC(0, UA_NS0ID_OBJECTSFOLDER),
                            UA_NODEID_NUMERIC(0, UA_NS0ID_HASCOMPONENT),
                            UA_QUALIFIEDNAME(1, "Enable Robot"),
                            enableRobot, &enableRobotMethodCallback,
                            0, NULL, 1, &outputArgument, NULL, NULL);
}