从键盘输入一个数据文件（字符串），储存并统计各字符以及各字符出现的次数，并为这些字符构造一棵哈夫曼树，设计并输出每个字符对应的哈夫曼编码的c++的代码

好的，以下是 C++ 代码实现：

#include <iostream>
#include <fstream>
#include <string>
#include <queue>
#include <unordered_map>
using namespace std;

struct TreeNode {
    char ch;
    int freq;
    TreeNode* left;
    TreeNode* right;
    TreeNode(char c, int f) : ch(c), freq(f), left(nullptr), right(nullptr) {}
};

struct Compare {
    bool operator() (const TreeNode* lhs, const TreeNode* rhs) const {
        return lhs->freq > rhs->freq;
    }
};

void getCharFreq(const string& filename, unordered_map<char, int>& freqMap) {
    ifstream file(filename);
    if (!file.is_open()) {
        cout << "Error opening file!" << endl;
        return;
    }
    char ch;
    while (file >> noskipws >> ch) {
        freqMap[ch]++;
    }
    file.close();
}

TreeNode* buildHuffmanTree(unordered_map<char, int>& freqMap) {
    priority_queue<TreeNode*, vector<TreeNode*>, Compare> pq;
    for (auto& p : freqMap) {
        pq.push(new TreeNode(p.first, p.second));
    }
    while (pq.size() > 1) {
        TreeNode* node1 = pq.top();
        pq.pop();
        TreeNode* node2 = pq.top();
        pq.pop();
        TreeNode* mergeNode = new TreeNode('$', node1->freq + node2->freq);
        mergeNode->left = node1;
        mergeNode->right = node2;
        pq.push(mergeNode);
    }
    return pq.top();
}

void getHuffmanCode(TreeNode* root, unordered_map<char, string>& codeMap, string code = "") {
    if (!root) {
        return;
    }
    if (root->ch != '$') {
        codeMap[root->ch] = code;
    }
    getHuffmanCode(root->left, codeMap, code + '0');
    getHuffmanCode(root->right, codeMap, code + '1');
}

void printHuffmanCode(unordered_map<char, string>& codeMap) {
    cout << "Huffman codes:" << endl;
    for (auto& p : codeMap) {
        cout << p.first << ": " << p.second << endl;
    }
}

int main() {
    string filename = "data.txt";
    unordered_map<char, int> freqMap;
    getCharFreq(filename, freqMap);
    TreeNode* root = buildHuffmanTree(freqMap);
    unordered_map<char, string> codeMap;
    getHuffmanCode(root, codeMap);
    printHuffmanCode(codeMap);
    return 0;
}

这个程序中，我们首先使用 `getCharFreq()` 函数从指定的文件中读取字符并统计它们的出现次数，然后使用 `buildHuffmanTree()` 函数构建哈夫曼树，最后使用 `getHuffmanCode()` 函数为每个字符生成哈夫曼编码，并使用 `printHuffmanCode()` 函数输出它们。