C ++结构错误“调用没有匹配功能……”

Question

I currently have the following structure(s)

struct LR0Item{
    string lhs;
    vector<string> rhs;
    int dpos;
};

struct Node{
    LR0Item* item;
    map<string, Node*> tr;
};

struct my_struct{
    bool operator()(
                    const LR0Item &a,
                    const LR0Item &b) {
                        if(a.lhs != b.lhs)
                            return a.lhs<b.lhs;
                        if(a.dpos != b.dpos)
                            return a.dpos<b.dpos;
                        return a.rhs<b.rhs;
                    }
};

and the following code:

vector<string> test_v;              //assume this is filled with various strings
vector<Node*> N;
map<LR0Item,Node*,my_struct> nmap;

LR0Item* Q = new LR0Item("test", test_v, 3);     //1 - error occurs here
Node* N1 = new Node(Q);                          //2 - error occurs here
N.push_back(N1);
nmap[*Q] = N1;

I am getting an error on comment 1 saying:

error: no matching function for call to 'LR0Item::LR0Item(std::string&, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >&, int&)'|
note: candidates are: LR0Item::LR0Item()|
note:                 LR0Item::LR0Item(const LR0Item&)

And my error at comment 2 saying:

error: no matching function for call to 'Node::Node(LR0Item*&)'
note: candidates are: Node::Node()|
note:                 Node::Node(const Node&)

I'm not entirely sure what is going on here or how to fix it.

EDIT: To clarify, not using C++11.

Answer 1

You need to make a constructor for LR0Item which matches the signature specified in the error message:

LR0Item::LR0Item(std::string&, std::vector<std::basic_string<char,
  std::char_traits<char>, std::allocator<char> >,
  std::allocator<std::basic_string<char, std::char_traits<char>, 
  std::allocator<char> > > >&, int&)

Simplifying the templates and fixing up the const-ness, of course that is:

LR0Item::LR0Item(const std::string&, const std::vector<std::string>&, int)

Answer 2

You have not created constuctors for your classes

You seem to want one for LR0Item(const String&, vector, int) and one for Node(const LR0Item&)

Add this to LR0Item:

LR0Item(const String& lhs_p, vector<string> rhs_p, int dpos_p)
     : lhs(lhs_p), rhs(rhs_p), dpos(dpos_p) {}

And add this to Node:

Node(LR0Item * lr) : item(lr) {}

In the {} add anything else you need to do for initialization

You will likely want to heve the copy constructor as well since once you define a constructor, you will not have the default ones available to you

Look more into constructors and overloading operator = if you want to understand this in more depth

Answer 3

In C++11 you can try the following:

// Brackets instead of parentheses
LR0Item* Q = new LR0Item{"test", test_v, 3};
Node* N1 = new Node{Q};

int main() {
N.push_back(N1);
nmap[*Q] = N1;
}

Answer 4

If you have a C++11 compiler then simply change the round parentheses in those calls, to curly braces .

Otherwise, for a C++03 compiler, define constructors .