C++解压与文件元数据管理

在C++中，解压文件和文件元数据管理的任务可以通过多种方式实现。以下是一些常用的方法和库：

1. 解压文件

使用 boost::iostreams 库

boost::iostreams 是一个强大的I/O库，可以用来处理压缩文件。以下是一个简单的示例，展示如何使用 boost::iostreams 解压 ZIP 文件：

#include <iostream>
#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filter/gzip.hpp>
#include <boost/iostreams/filter/bzip2.hpp>
#include <boost/iostreams/file_system.hpp>
#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filter/gzip.hpp>
#include <boost/iostreams/filter/bzip2.hpp>
#include <boost/iostreams/file_system.hpp>

namespace io = boost::iostreams;

int main() {
    std::string zip_file = "example.zip";
    std::string output_dir = "output";

    // 创建输出目录
    io::file_system::create_directory(output_dir);

    // 打开ZIP文件
    io::filtering_istream in;
    in.push(io::gzip_compressor());
    in.push(io::file_source(zip_file));

    // 解压文件到输出目录
    std::string filename;
    while (in >> filename) {
        std::string full_path = output_dir + "/" + filename;
        io::file_sink sink(full_path);
        io::copy(in, sink);
    }

    return 0;
}

使用 minizip 库

minizip 是一个轻量级的ZIP解压缩库，可以嵌入到C++项目中。以下是一个简单的示例：

#include <iostream>
#include <zip.h>
#include <unzip.h>
#include <vector>
#include <string>

int main() {
    const char* zip_file = "example.zip";
    unzFile uf = unzOpen(zip_file);
    if (uf == NULL) {
        std::cerr << "Failed to open zip file" << std::endl;
        return 1;
    }

    unz_global_info gi;
    unzGetGlobalInfo(uf, &gi);
    int num_entries = gi.number_entry;

    for (unsigned int i = 0; i < num_entries; ++i) {
        char filename[256];
        unzGetCurrentFileInfo(uf, NULL, filename, sizeof(filename), NULL, 0, NULL, 0);

        unzOpenCurrentFile(uf);
        std::vector<char> buffer(1024 * 1024);
        std::string output_path = "output/" + filename;
        std::ofstream outfile(output_path, std::ios::binary);
        if (!outfile) {
            std::cerr << "Failed to create output file: " << output_path << std::endl;
            continue;
        }

        int read;
        while ((read = unzReadCurrentFile(uf, buffer.data(), buffer.size())) > 0) {
            outfile.write(buffer.data(), read);
        }

        unzCloseCurrentFile(uf);
        if (read < 0) {
            std::cerr << "Error reading file: " << filename << std::endl;
        }
    }

    unzClose(uf);
    return 0;
}

2. 文件元数据管理

使用 boost::property_tree 库

boost::property_tree 是一个用于处理XML和JSON数据的库，可以用来管理文件元数据。以下是一个简单的示例：

#include <iostream>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <boost/property_tree/xml_parser.hpp>

namespace pt = boost::property_tree;

int main() {
    // 读取JSON元数据
    std::string json_data = R"(
    {
        "file1": {
            "size": 1024,
            "type": "text",
            "modified": "2023-04-01"
        },
        "file2": {
            "size": 2048,
            "type": "binary",
            "modified": "2023-04-02"
        }
    }
    )";

    pt::ptree tree;
    pt::read_json(std::istringstream(json_data), tree);

    // 输出元数据
    for (const auto& pair : tree.get_child("files")) {
        std::string name = pair.first;
        const pt::ptree& file = pair.second;
        std::cout << "File: " << name << std::endl;
        std::cout << "Size: " << file.get<int>("size") << std::endl;
        std::cout << "Type: " << file.get<std::string>("type") << std::endl;
        std::cout << "Modified: " << file.get<std::string>("modified") << std::endl;
    }

    return 0;
}

使用 SQLite 数据库

SQLite 是一个轻量级的嵌入式数据库，可以用来管理文件元数据。以下是一个简单的示例：

#include <iostream>
#include <sqlite3.h>
#include <string>

static int callback(void* data, int argc, char** argv, char** azColName) {
    for (int i = 0; i < argc; i++) {
        std::cout << azColName[i] << ": " << (argv[i] ? argv[i] : "NULL") << std::endl;
    }
    std::cout << std::endl;
    return 0;
}

int main() {
    sqlite3* db;
    char* errorMessage = nullptr;

    int exitcode = sqlite3_open("files.db", &db);
    if (exitcode) {
        std::cerr << "Can't open database: " << sqlite3_errmsg(db) << std::endl;
        return 1;
    }

    std::string sql = "CREATE TABLE IF NOT EXISTS files ("
                      "id INTEGER PRIMARY KEY AUTOINCREMENT, "
                      "name TEXT NOT NULL, "
                      "size INTEGER NOT NULL, "
                      "type TEXT NOT NULL, "
                      "modified TEXT NOT NULL);";

    exitcode = sqlite3_exec(db, sql.c_str(), callback, nullptr, &errorMessage);
    if (exitcode != SQLITE_OK) {
        std::cerr << "SQL error: " << errorMessage << std::endl;
        sqlite3_free(errorMessage);
        return 1;
    }

    // 插入元数据
    sql = "INSERT INTO files (name, size, type, modified) VALUES ('file1', 1024, 'text', '2023-04-01');";
    exitcode = sqlite3_exec(db, sql.c_str(), callback, nullptr, &errorMessage);
    if (exitcode != SQLITE_OK) {
        std::cerr << "SQL error: " << errorMessage << std::endl;
        sqlite3_free(errorMessage);
        return 1;
    }

    sql = "INSERT INTO files (name, size, type, modified) VALUES ('file2', 2048, 'binary', '2023-04-02');";
    exitcode = sqlite3_exec(db, sql.c_str(), callback, nullptr, &errorMessage);
    if (exitcode != SQLITE_OK) {
        std::cerr << "SQL error: " << errorMessage << std::endl;
        sqlite3_free(errorMessage);
        return 1;
    }

    // 查询元数据
    sql = "SELECT * FROM files;";
    exitcode = sqlite3_exec(db, sql.c_str(), callback, nullptr, &errorMessage);
    if (exitcode != SQLITE_OK) {
        std::cerr << "SQL error: " << errorMessage << std::endl;
        sqlite3_free(errorMessage);
        return 1;
    }

    sqlite3_close(db);
    return 0;
}

这些示例展示了如何在C++中解压文件和管理文件元数据。根据具体需求，可以选择合适的库和方法来实现所需的功能。