Programming Forums > Application Development > C++

titaniumdecoy · Mar 31st, 2006, 11:40 PM

I need help getting the following code to compile. I am writing a set class implemented as a binary search tree of strings, and have started writing a header file, but for some reason the insert(...) method is causing me problems. I have commented out the .cpp file to get this to work but it does not.

(Toggle Plain Text)

#include <string>
#include <cstdlib>
using std::string;

class BSTSet {
  public:
    BSTSet();

    void insert(string s, TreeNode *node = root); // <-- this is the problem

  private:
    class TreeNode {
      public:
        TreeNode(string s, TreeNode *l = NULL, TreeNode *r = NULL);
        string value;
        TreeNode *left, *right;
    };
    TreeNode *root;
};

I get the following error when I try to compile this:

(Toggle Plain Text)

BSTSet.h:19: type specifier omitted for parameter `TreeNode'
BSTSet.h:19: parse error before `*' token

I have tried adding incomplete class declarations such as "class BSTSet::TreeNode;" and "class TreeNode" but I can't seem to figure out the problem. Please help! Thanks.

hbe02 · Apr 1st, 2006, 2:35 AM

I rearranged your code a little. i think i clearer like that, you dont need to include a class inside another.
i saw that you had (.....TreeNode *r = root) in the insert function. this made no sense to me, since the insert function should take a node pointer and insert it as a left child or right child of the root, and so on....
basicly the insert function CHANGES the root..
have fun with the rest.. it would be cooler if you made a template element instead of string though, this way your tree can take anything from integers to even objects..

(Toggle Plain Text)

#include <string>
#include <cstdlib>
using std::string;

class TreeNode {
	private:
		string value;
        TreeNode* left;
		TreeNode* right;

      public:
        TreeNode(string s, TreeNode *l = NULL, TreeNode *r = NULL)
		{
			value = s;
			left = l;
			right = r;
		}
        
    };

class BSTSet {
  private:
	TreeNode *root;
  public:
    BSTSet();

 void insert( string s = NULL, TreeNode *node = NULL ) 
	{
		root = node; //do this if tree is empty else you change the root would have a new child/sibling...
	}

};

void main()
{

}

Jimbo · Apr 1st, 2006, 3:15 AM

Remember that unlike in Java, types (and functions) must be declared before they can be used in C++. Rearranging fixed the problem as the class was then defined at the time when you referenced it. And as hbe02 suggested, once you get your BST working, try it with templates

grumpy · Apr 1st, 2006, 3:34 AM

There are actually two problems in the code. Firstly, before you can pass a pointer to a function, there needs to be (at a minimum) a forward declaration of the type you are passing. Second, default arguments to functions need to be resolvable to an actual value at compile time. So "root" needs to be some_static_object.root or NULL.

The default value for an argument of a non-static member function cannot be a non-static member of the class. There are two alternatives;

(Toggle Plain Text)

#include <string>
#include <cstdlib>

class BSTSet {
  public:
    BSTSet();

    class BSTSet::TreeNode;   // so we can declare functions that accept a pointer to TreeNode

    void insert(const std::string &s, TreeNode *node);

    void insert(const std::string &s) {insert(s, root);};

  private:
    class TreeNode {
      public:
        TreeNode(const std::string s, TreeNode *l = NULL, TreeNode *r = NULL);
        std::string value;
        TreeNode *left, *right;
    };
    TreeNode *root;
};

OR;

(Toggle Plain Text)

#include <string>
#include <cstdlib>

class BSTSet {
  public:
    BSTSet();

    class BSTSet::TreeNode;   // so we can declare functions that accept a pointer to TreeNode

    void insert(const std::string &s, TreeNode *node = 0)
    {
           if (!node) node = root;
           // all the code you intended to have.....
    };

  private:
    class TreeNode {
      public:
        TreeNode(const std::string s, TreeNode *l = NULL, TreeNode *r = NULL);
        std::string value;
        TreeNode *left, *right;
    };
    TreeNode *root;
};

One other thing that I've fixed as an aside: eventually, as a project gets bigger, class declarations get moved into separate header files. It is A VERY BAD IDEA to place a using directive into a header file at file scope. That usually means that, if you want a class to have a member of type std::string in a class, it is better to avoid a using directive and to employ the full name (std::string) within the class declaration.

Mar 31st, 2006, 11:40 PM	#1
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 843 Rep Power: 3	Error: Type Specifier Omitted? I need help getting the following code to compile. I am writing a set class implemented as a binary search tree of strings, and have started writing a header file, but for some reason the insert(...) method is causing me problems. I have commented out the .cpp file to get this to work but it does not. (Toggle Plain Text) #include <string> #include <cstdlib> using std::string; class BSTSet { public: BSTSet(); void insert(string s, TreeNode node = root); // <-- this is the problem private: class TreeNode { public: TreeNode(string s, TreeNode l = NULL, TreeNode r = NULL); string value; TreeNode left, right; }; TreeNode root; }; #include <string> #include <cstdlib> using std::string; class BSTSet { public: BSTSet(); void insert(string s, TreeNode node = root); // <-- this is the problem private: class TreeNode { public: TreeNode(string s, TreeNode l = NULL, TreeNode r = NULL); string value; TreeNode left, right; }; TreeNode root; }; I get the following error when I try to compile this: (Toggle Plain Text) BSTSet.h:19: type specifier omitted for parameter `TreeNode' BSTSet.h:19: parse error before `' token BSTSet.h:19: type specifier omitted for parameter `TreeNode' BSTSet.h:19: parse error before `' token I have tried adding incomplete class declarations such as "class BSTSet::TreeNode;" and "class TreeNode" but I can't seem to figure out the problem. Please help! Thanks.

Apr 1st, 2006, 2:35 AM	#2
hbe02 Hobbyist Programmer Join Date: Mar 2006 Location: Lebanon Posts: 148 Rep Power: 3	I rearranged your code a little. i think i clearer like that, you dont need to include a class inside another. i saw that you had (.....TreeNode r = root) in the insert function. this made no sense to me, since the insert function should take a node pointer and insert it as a left child or right child of the root, and so on.... basicly the insert function CHANGES the root.. have fun with the rest.. it would be cooler if you made a template element instead of string though, this way your tree can take anything from integers to even objects.. (Toggle Plain Text) #include <string> #include <cstdlib> using std::string; class TreeNode { private: string value; TreeNode left; TreeNode* right; public: TreeNode(string s, TreeNode l = NULL, TreeNode r = NULL) { value = s; left = l; right = r; } }; class BSTSet { private: TreeNode root; public: BSTSet(); void insert( string s = NULL, TreeNode node = NULL ) { root = node; //do this if tree is empty else you change the root would have a new child/sibling... } }; void main() { } #include <string> #include <cstdlib> using std::string; class TreeNode { private: string value; TreeNode* left; TreeNode* right; public: TreeNode(string s, TreeNode l = NULL, TreeNode r = NULL) { value = s; left = l; right = r; } }; class BSTSet { private: TreeNode root; public: BSTSet(); void insert( string s = NULL, TreeNode node = NULL ) { root = node; //do this if tree is empty else you change the root would have a new child/sibling... } }; void main() { }

Apr 1st, 2006, 3:34 AM	#4
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,207 Rep Power: 5	There are actually two problems in the code. Firstly, before you can pass a pointer to a function, there needs to be (at a minimum) a forward declaration of the type you are passing. Second, default arguments to functions need to be resolvable to an actual value at compile time. So "root" needs to be some_static_object.root or NULL. The default value for an argument of a non-static member function cannot be a non-static member of the class. There are two alternatives; (Toggle Plain Text) #include <string> #include <cstdlib> class BSTSet { public: BSTSet(); class BSTSet::TreeNode; // so we can declare functions that accept a pointer to TreeNode void insert(const std::string &s, TreeNode node); void insert(const std::string &s) {insert(s, root);}; private: class TreeNode { public: TreeNode(const std::string s, TreeNode l = NULL, TreeNode r = NULL); std::string value; TreeNode left, right; }; TreeNode root; }; #include <string> #include <cstdlib> class BSTSet { public: BSTSet(); class BSTSet::TreeNode; // so we can declare functions that accept a pointer to TreeNode void insert(const std::string &s, TreeNode node); void insert(const std::string &s) {insert(s, root);}; private: class TreeNode { public: TreeNode(const std::string s, TreeNode l = NULL, TreeNode r = NULL); std::string value; TreeNode left, right; }; TreeNode root; }; OR; (Toggle Plain Text) #include <string> #include <cstdlib> class BSTSet { public: BSTSet(); class BSTSet::TreeNode; // so we can declare functions that accept a pointer to TreeNode void insert(const std::string &s, TreeNode node = 0) { if (!node) node = root; // all the code you intended to have..... }; private: class TreeNode { public: TreeNode(const std::string s, TreeNode l = NULL, TreeNode r = NULL); std::string value; TreeNode left, right; }; TreeNode root; }; #include <string> #include <cstdlib> class BSTSet { public: BSTSet(); class BSTSet::TreeNode; // so we can declare functions that accept a pointer to TreeNode void insert(const std::string &s, TreeNode node = 0) { if (!node) node = root; // all the code you intended to have..... }; private: class TreeNode { public: TreeNode(const std::string s, TreeNode l = NULL, TreeNode r = NULL); std::string value; TreeNode left, right; }; TreeNode root; }; One other thing that I've fixed as an aside: eventually, as a project gets bigger, class declarations get moved into separate header files. It is A VERY BAD IDEA to place a using directive into a header file at file scope. That usually means that, if you want a class to have a member of type std::string in a class, it is better to avoid a using directive and to employ the full name (std::string) within the class declaration.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Apr 1st, 2006, 3:15 AM	#3
Jimbo Battle Programmer Join Date: Feb 2006 Location: Bellevue, WA, USA Posts: 754 Rep Power: 3	Remember that unlike in Java, types (and functions) must be declared before they can be used in C++. Rearranging fixed the problem as the class was then defined at the time when you referenced it. And as hbe02 suggested, once you get your BST working, try it with templates

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Programming Forums > Application Development > C++

Error: Type Specifier Omitted?