文件压缩程序的设计与实现代码C++

以下是一个简单的文件压缩程序的设计与实现代码 C++：

#include<iostream>
#include<fstream>
#include<cstring>
#include<cstdlib>

using namespace std;

// 定义常量
const int MAXCHAR = 256;  // 最大字符数
const int MAXNODE = 511;  // 最大节点数
const int MAXBIT = 1000;  // 最大比特数

// 压缩文件结构体
struct compressfile {
    char name[100];  // 文件名
    int freq[MAXCHAR];  // 字符出现频率
    char code[MAXCHAR][MAXBIT];  // 字符编码
    int len[MAXCHAR];  // 字符编码长度
} cf;

// 哈夫曼树结点结构体
struct node {
    int freq;  // 字符出现频率
    int parent, lchild, rchild;  // 父节点、左孩子、右孩子
} tree[MAXNODE];

// 创建哈夫曼树
void createTree(int n) {
    int i, j, x1, x2;
    double min1, min2;
    for (i = 1; i <= n; i++) {
        tree[i].freq = cf.freq[i - 1];
        tree[i].parent = tree[i].lchild = tree[i].rchild = 0;
    }
    for (i = n + 1; i <= 2 * n - 1; i++) {
        min1 = min2 = 1e9;
        x1 = x2 = 0;
        for (j = 1; j < i; j++) {
            if (!tree[j].parent) {
                if (tree[j].freq < min1) {
                    min2 = min1;
                    x2 = x1;
                    min1 = tree[j].freq;
                    x1 = j;
                } else if (tree[j].freq < min2) {
                    min2 = tree[j].freq;
                    x2 = j;
                }
            }
        }
        tree[x1].parent = i;
        tree[x2].parent = i;
        tree[i].lchild = x1;
        tree[i].rchild = x2;
        tree[i].freq = tree[x1].freq + tree[x2].freq;
    }
}

// 编码
void encode(int n) {
    int i, j, k, p;
    char code[MAXBIT];
    for (i = 0; i < n; i++) {
        p = i + 1;
        k = 0;
        j = tree[p].parent;
        while (j) {
            if (tree[j].lchild == p) code[k++] = '0';
            else code[k++] = '1';
            p = j;
            j = tree[p].parent;
        }
        code[k] = '\0';
        strcpy(cf.code[i], strrev(code));
        cf.len[i] = k;
    }
}

// 压缩文件
void compress(char *filename) {
    char *p, c;
    int i, j, len, sum = 0;
    ifstream fin(filename, ios::binary);
    while (!fin.eof()) {
        fin.get(c);
        if (fin.eof()) break;
        cf.freq[c]++;
        sum++;
    }
    fin.close();
    createTree(256);
    encode(256);
    p = strrchr(filename, '.');
    strcpy(cf.name, filename);
    len = strlen(cf.name);
    cf.name[len] = 'h';
    cf.name[len + 1] = 'f';
    cf.name[len + 2] = '\0';
    ofstream fout(cf.name, ios::binary);
    fout.write((char *) &sum, sizeof(int));
    for (i = 0; i < 256; i++)
        fout.write((char *) &cf.freq[i], sizeof(int));
    fin.open(filename, ios::binary);
    c = 0;
    len = 0;
    while (!fin.eof()) {
        fin.get(p[0]);
        if (fin.eof()) break;
        i = p[0];
        len += cf.len[i];
        for (j = 0; j < cf.len[i]; j++) {
            c <<= 1;
            if (cf.code[i][j] == '1') c |= 1;
            if (len == 8) {
                fout.put(c);
                c = 0;
                len = 0;
            }
        }
    }
    if (len > 0) {
        c <<= (8 - len);
        fout.put(c);
    }
    fin.close();
    fout.close();
}

// 解压缩文件
void decompress(char *filename) {
    char *p, c, code[MAXBIT];
    int i, j, len, sum = 0;
    ifstream fin(filename, ios::binary);
    fin.read((char *) &sum, sizeof(int));
    for (i = 0; i < 256; i++)
        fin.read((char *) &cf.freq[i], sizeof(int));
    createTree(256);
    p = strrchr(filename, '.');
    p++;
    *p = 'd';
    *(p + 1) = 'a';
    *(p + 2) = 't';
    *(p + 3) = '\0';
    ofstream fout(p, ios::binary);
    len = 0;
    i = 2 * MAXNODE - 2;
    while (sum > 0) {
        fin.get(c);
        for (j = 7; j >= 0 && sum > 0; j--) {
            if ((c >> j) & 1) i = tree[i].rchild;
            else i = tree[i].lchild;
            if (!tree[i].lchild) {
                fout.put(i);
                sum--;
                i = 2 * MAXNODE - 2;
            }
        }
    }
    fin.close();
    fout.close();
}

int main() {
    char filename[100];
    int choice;
    while (true) {
        cout << "1. 压缩文件" << endl;
        cout << "2. 解压缩文件" << endl;
        cout << "3. 退出" << endl;
        cout << "请选择：";
        cin >> choice;
        switch (choice) {
            case 1:
                cout << "请输入要压缩的文件名：";
                cin >> filename;
                compress(filename);
                cout << "压缩完成!" << endl;
                break;
            case 2:
                cout << "请输入要解压缩的文件名：";
                cin >> filename;
                decompress(filename);
                cout << "解压缩完成!" << endl;
                break;
            case 3:
                exit(0);
            default:
                cout << "输入错误，请重新输入!" << endl;
        }
    }
    return 0;
}

该程序实现了简单的文件压缩和解压缩功能，使用哈夫曼编码实现数据压缩，具体实现过程在代码注释中进行了解释。