C++利用Ｓｑｌｉｔｅ3写一个辅助类能够进行数据库的创建增删改查等功能，支持数据库备份功能

好的，以下是一个简单的 C++ 辅助类，可以进行 SQLite3 数据库的创建、增、删、改、查和备份等操作。

首先需要安装 SQLite3，并在项目中链接 SQLite3 库。

辅助类头文件（DatabaseHelper.h）：

#ifndef DATABASEHELPER_H
#define DATABASEHELPER_H

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

class DatabaseHelper
{
public:
    DatabaseHelper(const std::string& dbname);
    virtual ~DatabaseHelper();

    bool open();
    void close();

    bool execute(const std::string& sql);

    bool tableExists(const std::string& tablename);
    bool createTable(const std::string& tablename, const std::string& fields);
    bool dropTable(const std::string& tablename);

    bool insert(const std::string& tablename, const std::string& fields, const std::string& values);
    bool update(const std::string& tablename, const std::string& fields, const std::string& values, const std::string& where);
    bool remove(const std::string& tablename, const std::string& where);

    bool backup(const std::string& backupfile);

private:
    sqlite3* db;
    std::string dbname;
};

#endif // DATABASEHELPER_H

辅助类实现文件（DatabaseHelper.cpp）：

#include "DatabaseHelper.h"
#include <iostream>
#include <fstream>

DatabaseHelper::DatabaseHelper(const std::string& dbname)
    : db(nullptr), dbname(dbname)
{
}

DatabaseHelper::~DatabaseHelper()
{
    close();
}

bool DatabaseHelper::open()
{
    int rc = sqlite3_open(dbname.c_str(), &db);
    if (rc != SQLITE_OK)
    {
        std::cerr << "Can't open database: " << sqlite3_errmsg(db) << std::endl;
        sqlite3_close(db);
        db = nullptr;
        return false;
    }
    return true;
}

void DatabaseHelper::close()
{
    if (db)
    {
        sqlite3_close(db);
        db = nullptr;
    }
}

bool DatabaseHelper::execute(const std::string& sql)
{
    char* errmsg = nullptr;
    int rc = sqlite3_exec(db, sql.c_str(), nullptr, nullptr, &errmsg);
    if (rc != SQLITE_OK)
    {
        std::cerr << "SQL error: " << errmsg << std::endl;
        sqlite3_free(errmsg);
        return false;
    }
    return true;
}

bool DatabaseHelper::tableExists(const std::string& tablename)
{
    std::string sql = "SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND name='" + tablename + "'";
    sqlite3_stmt* stmt = nullptr;
    int rc = sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr);
    if (rc != SQLITE_OK)
    {
        std::cerr << "Can't prepare SQL statement: " << sqlite3_errmsg(db) << std::endl;
        return false;
    }
    rc = sqlite3_step(stmt);
    if (rc != SQLITE_ROW)
    {
        std::cerr << "Can't get result: " << sqlite3_errmsg(db) << std::endl;
        sqlite3_finalize(stmt);
        return false;
    }
    int count = sqlite3_column_int(stmt, 0);
    sqlite3_finalize(stmt);
    return count == 1;
}

bool DatabaseHelper::createTable(const std::string& tablename, const std::string& fields)
{
    if (tableExists(tablename))
    {
        std::cerr << "Table already exists: " << tablename << std::endl;
        return false;
    }
    std::string sql = "CREATE TABLE " + tablename + "(" + fields + ")";
    return execute(sql);
}

bool DatabaseHelper::dropTable(const std::string& tablename)
{
    if (!tableExists(tablename))
    {
        std::cerr << "Table does not exist: " << tablename << std::endl;
        return false;
    }
    std::string sql = "DROP TABLE " + tablename;
    return execute(sql);
}

bool DatabaseHelper::insert(const std::string& tablename, const std::string& fields, const std::string& values)
{
    std::string sql = "INSERT INTO " + tablename + "(" + fields + ") VALUES(" + values + ")";
    return execute(sql);
}

bool DatabaseHelper::update(const std::string& tablename, const std::string& fields, const std::string& values, const std::string& where)
{
    std::string sql = "UPDATE " + tablename + " SET " + fields + "='" + values + "' WHERE " + where;
    return execute(sql);
}

bool DatabaseHelper::remove(const std::string& tablename, const std::string& where)
{
    std::string sql = "DELETE FROM " + tablename + " WHERE " + where;
    return execute(sql);
}

bool DatabaseHelper::backup(const std::string& backupfile)
{
    std::ifstream src(dbname, std::ios::binary);
    std::ofstream dst(backupfile, std::ios::binary);
    dst << src.rdbuf();
    return true;
}

使用示例：

#include "DatabaseHelper.h"

int main()
{
    // 创建辅助类对象
    DatabaseHelper dbhelper("test.db");

    // 打开数据库
    if (!dbhelper.open())
    {
        return -1;
    }

    // 创建表
    dbhelper.createTable("user", "id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER");

    // 插入数据
    dbhelper.insert("user", "name, age", "'Tom', 20");

    // 查询数据
    sqlite3_stmt* stmt = nullptr;
    std::string sql = "SELECT * FROM user";
    int rc = sqlite3_prepare_v2(dbhelper.db, sql.c_str(), -1, &stmt, nullptr);
    if (rc == SQLITE_OK)
    {
        while (sqlite3_step(stmt) == SQLITE_ROW)
        {
            int id = sqlite3_column_int(stmt, 0);
            const unsigned char* name = sqlite3_column_text(stmt, 1);
            int age = sqlite3_column_int(stmt, 2);
            std::cout << "id=" << id << ", name=" << name << ", age=" << age << std::endl;
        }
        sqlite3_finalize(stmt);
    }

    // 更新数据
    dbhelper.update("user", "age", "21", "name='Tom'");

    // 删除数据
    dbhelper.remove("user", "name='Tom'");

    // 数据库备份
    dbhelper.backup("test_backup.db");

    // 关闭数据库
    dbhelper.close();

    return 0;
}

注意：上述代码只是一个简单的示例，没有进行错误处理、SQL 注入等安全性考虑，实际使用时需要根据具体需求进行完善。