C++ - 将rapidjson::Document 作为参数传递给函数

Question

I'm passing pointer to rapidjson::Document as an argument.

foo(rapidjson::Document* jsonDocument)
{
    std::cout << jsonDocument["name"] << std::endl;
}

But I cannot do jsonDocument["name"] to access the name attribute.

Attempting to not use pointers leads to an error:

error: 'rapidjson::GenericDocument<Encoding, Allocator, StackAllocator>::GenericDocument(const rapidjson::GenericDocument<Encoding, Allocator, StackAllocator>&) [with Encoding = rapidjson::UTF8<>; Allocator = rapidjson::MemoryPoolAllocator<>; StackAllocator = rapidjson::CrtAllocator]' is private
GenericDocument(const GenericDocument&);

Can someone help me?

Answer 1

Use a reference or a value as argument. Using the [] with a pointer will try to use your document as if it was an array of document. A reference or a value will call the expected operator.

// a const reference
foo(const rapidjson::Document& jsonDocument) {
    std::cout << jsonDocument["name"] << std::endl;
}

// a copy (or move)
foo(rapidjson::Document jsonDocument) {
    std::cout << jsonDocument["name"] << std::endl;
}

I'd recommend you to use the reference, as your function don't need to consume any resources in the document, but only observe and print a value.

The call of this function will look like this:

rapidjson::Document doc = /* ... */;

foo(doc);