C++ Compilation Error Non Class Type

Question

In below I am getting error as error: request for member 'get_id' in '* it', which is of non-class type 'const Param* const'. What is the problem with below piece of code

bool SomeParams::is_default(int _id) const
{
        vector<const Param*> param_list;
        bool is_default = false;

        if( get_default_params(param_list) ) // This populates param_list
        {
                vector<const Param*>::const_iterator it = param_list.begin();

                for(;it!=param_list.end();++it)
                {
                        if( *it->get_id() == _id ) // get_id is function in Param object
                        {
                                is_default = true;
                                break;
                        }
                }
        }

        return is_default;
}

Answer 1

Precendece of -> (ie member access operator) is higher than * (ie indirection operator), so

*it->get_id();

is interpreted as:

*(it->get_id()); 

which causes compilation error.

What you need is this:

(*it)->get_id();

See this table:

• C++ Operator Precedence

---

Two important points:

• The name of the parameter of the function starts with _ , which according to the language specification, invokes undefined behavior. Names starting with an underscore are reserved. Don't use them.

• The function's name is is_default , and there is one variable inside the function, which is also is_default . Why don't you choose different name for the variable? That would increase the readability of your code.

Answer 2

将*it括在括号中： (*it)->get_id() 。