How to convert const UA_Variant *input to std::string

[Vojtěch Houdek]

Hello,
i am a junior dev in c ++ and i am trying to convert the parameter of the function "static UA_StatusCode ... (...., const UA_Variant * input)" inside the body of this function to the classic std::string data type. I've tried many ways and it still doesn't work. The input data are valid. When I  do convert I always get meaningless numbers.
I also tried to come up with an algorithm for conversion using the original value uint8_t which represents UA_Byte which is contained in UA_String.data, but none of this came out.

I hope it is understandable. Thank you for any response.

[Jijun MA]

Hello,

this works for me:

#include <open62541/types_generated.h>

#include <open62541/types.h>

#include <iostream>

using namespace std;

void set_str_to_variant(UA_Variant *var) {

    char hello[] = "hello";

    auto ua_hello = UA_STRING(hello);

    UA_Variant_setScalarCopy(var, &ua_hello, &UA_TYPES[UA_TYPES_STRING]);

}

string get_str_from_variant(UA_Variant *var) {

    auto str = (UA_String *)var->data;

    return (char *)str->data;

}

int main()

{

    UA_Variant ua_var;

    set_str_to_variant(&ua_var);

    cout << get_str_from_variant(&ua_var);

}

---

From: open...@googlegroups.com <open...@googlegroups.com> on behalf of Vojtěch Houdek <vojt...@gmail.com>
Sent: Wednesday, April 27, 2022 20:26
To: open62541 <open...@googlegroups.com>
Subject: [open62541] How to convert const UA_Variant *input to std::string

 

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[Julius Pfrommer]

Thanks Kim for the solution.

I would make a small addition.

You are directly casting from (char*) to a std:string.

That works in this case because the original memory is zero-terminated.

But that is not always the case.

In open62541 we track the length of strings explicitly.

So you can build your std::string as follows:

std::string((char *)str->data, str->length);

That is even a speed improvement because there is no need to scan for the terminating zero.

Regards, Julius