CODEWITHSUNDEEP
c++classtemplatesstl
Citron
Citron

Reputation: 13

C++ class templates argument invalid

I want to define a binary tree class template like this:

template<typename Any>
class tree {
    public:
        struct treeNode {
            Any &_data;
            treeNode *_left, *_right;
            treeNode(const Any &data, treeNode *left = nullptr,
                     treeNode *right = nullptr) :
                     _data(data), _left(left), _right(right) {
            }
        };
    // ...
        std::vector<treeNode *> lookfor(
                const treeNode *, const std::function<bool(const Any &)> &) const;
};

// ↑ tree.h
// ↓ tree.cpp

template<typename Any>
std::vector<tree::treeNode *> tree<Any>::lookfor(
        const treeNode *x, const std::function<bool(const Any &)> &cmp) const {
    // ...
}

Then g++ was not happy and told me this:

tree.cpp:129:29: error: template argument 1 is invalid
 std::vector<tree::treeNode *> tree<Any>::lookfor(
                             ^
tree.cpp:129:29: error: template argument 2 is invalid
tree.cpp:129:31: error: prototype for ‘int tree<Any>::lookfor(const tree<Any>::treeNode*, const std::function<bool(const Any&)>&) const’ does not match any in class ‘tree<Any>’
 std::vector<tree::treeNode *> tree<Any>::lookfor(
                               ^
In file included from tree.cpp:1:0:
tree.h:88:33: error:                 std::vector<tree<Any>::treeNode*> tree<Any>::lookfor(const tree<Any>::treeNode*, const std::function<bool(const Any&)>&) const
         std::vector<treeNode *> lookfor(
                                 ^

So I wonder why it happened and how I can fix this bug.

I'm not good at English and this is my first time asking a question on statckoverflow so if I have made any mistake please tell me :)

Upvotes: 1

Views: 1522

Answers (1)

MatiasFG
MatiasFG

Reputation: 576

The code:

std::vector<tree::treeNode *> tree<Any>::lookfor

Is referencing tree, which is a template, without template arguments. It should be something like:

std::vector<typename tree<Any>::treeNode *> tree<Any>::lookfor

Also, as these are templates you shouldn't have a .cpp file for tree, that is also causing problems.

Upvotes: 5

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