模板使用代码错误

Question

我最近开始学习C ++，并且对理解模板机制有疑问。 首先，任务是构建用户定义的二叉树。 我无法编译我的代码。

#include <iostream>
using namespace std;
template <typename DataType> struct TreeNode
{
    TreeNode(DataType val, TreeNode *leftPtr = null, TreeNode *rightPtr = null)
    {
        left = leftPtr;
        right = rightPtr;
        data = val;
    }
    TreeNode *left, *right;
    DataType data;
};
template <typename DataType> TreeNode *BuildTree()
{
    TreeNode *root = new TreeNode(10, new TreeNode(20), new TreeNode(30));

    TreeNode *curRoot = root;
    curRoot = curRoot->left;
    curRoot->left = new TreeNode(40);
    curRoot->left->left = new TreeNode(70);
    curRoot->right = new TreeNode(50);
    curRoot = curRoot->right;
    curRoot->left = new TreeNode(80, new TreeNode(100), new TreeNode(110));
    curRoot = root->right;
    curRoot->left = new TreeNode(60);
    curRoot = curRoot->left;
    curRoot->right = new TreeNode(90, new TreeNode(120), new TreeNode(130));

    return root;
}
int main()
{
    TreeNode *treeRoot = BuildTree<int>();
    cin.get();
    return 0;
}

函数BuildTree用具体的数据类型构建树的具体实例。 请帮助我理解我的错误。 请不要注意我使用后没有释放内存的事实。 那只是草稿。

Answer 1

由于TreeNode是模板类，因此在使用它时必须指定专业化：

template <typename DataType> TreeNode *BuildTree()

应该

template <typename DataType> TreeNode<DataType> *BuildTree()

和

TreeNode *root = new TreeNode(10, new TreeNode(20), new TreeNode(30));

应该

TreeNode<DataType> *root = new TreeNode(10, new TreeNode(20), new TreeNode(30));

方法中的其他内容，以及main ：

TreeNode<int> *treeRoot = BuildTree<int>();

代替

TreeNode *treeRoot = BuildTree<int>();

Answer 2

我认为您的代码应如下所示：

#include <iostream>
using namespace std;
template <typename DataType> struct TreeNode
{
    TreeNode(DataType val, TreeNode<DataType> *leftPtr = null, TreeNode<DataType> *rightPtr = null)
    {
        left = leftPtr;
        right = rightPtr;
        data = val;
    }
    TreeNode<DataType> *left, *right;
    DataType data;
};
template <typename DataType> TreeNode<DataType> *BuildTree()
{
    TreeNode<DataType> *root = new TreeNode(10, new TreeNode<DataType>(20), new TreeNode<DataType>(30));

    TreeNode<DataType> *curRoot = root;
    curRoot = curRoot->left;
    curRoot->left = new TreeNode<DataType>(40);
    curRoot->left->left = new TreeNode<DataType>(70);
    curRoot->right = new TreeNode<DataType>(50);
    curRoot = curRoot->right;
    curRoot->left = new TreeNode<DataType>(80, new TreeNode<DataType>(100), new TreeNode<DataType>(110));
    curRoot = root->right;
    curRoot->left = new TreeNode<DataType>(60);
    curRoot = curRoot->left;
    curRoot->right = new TreeNode<DataType>(90, new TreeNode<DataType>(120), new TreeNode<DataType>(130));

    return root;
}
int main()
{
    TreeNode<int> *treeRoot = BuildTree<int>();
    cin.get();
    return 0;
}