CODEWITHSUNDEEP
c++stdunordered-map
user650261
user650261

Reputation: 2265

accessing unordered_maps as pointers

For some reason, I am having trouble editing values in my unordered_map, and am wondering what I'm doing wrong.

In the following code, parameteris a struct. For some reason, the following code is throwing a syntax error, not liking the [.

void MyClass::setParameter(string name, parameter param) {
    if (this->param_name_to_data == nullptr) {
        //create it lazily
        this->param_name_to_data = new unordered_map<string, parameter>();
    }
    this->param_name_to_data->[name] = param;
}

The dictionary id declared in the corresponding .h file as:

private:
 std::unordered_map<std::string, parameter> * param_name_to_data = nullptr;

What am I doing wrong?

Upvotes: 0

Views: 1454

Answers (1)

David Haim
David Haim

Reputation: 26536

param_name_to_data->[name] = param; is not a valid syntax

when the compiler sees -> it looks for either a member variable or a member function. the statement ->[...] is meaningless since [] alone is neither a member variable nor a function.

you can write instead

(*param_name_to_data)[name] = param;

or turn the pointer to reference first

auto& map = *param_name_to_data;
map[name] = param;

you can also use the ugly literal form of 

param_name_to_data->operator[] (name) = param

but the last one is discouraged.

Upvotes: 4

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