C++ 抽象数据库在C+中的实现+；

我想通过从Db继承创建抽象Db类并实现Pg（postgresql）：

Db.h：

template <class T>
class Db 
{
public:
    Db(std::string, std::string, std::string, std::string);
    virtual ~Db();

protected:
    T* getConnection();
    std::string getHost();
    std::string getUsername();
    std::string getDatabase();
    std::string getPassword();
    virtual std::string getConnectionString()=0;

private: 
    T* connection;
    std::string host;
    std::string username;
    std::string database;
    std::string password;
};

#include "Db.h"

using namespace std;

template <class T>
Db<T>::Db(string iHost, string iUsername, string iDatabase, string iPassword) 
    : host(iHost), username(iUsername), database(iDatabase), password(iPassword) {
    T* conn(getConnectionString());
    connection = conn;
}

template <class T>
T* Db<T>::getConnection() {
    return connection;
}

... getters

#include "../Db.h"

template <class T>
class Pg : public Db<T> {
public:
    virtual std::string getConnectionString();
};

#include "Pg.h"

template <class T>
std::string Pg<T>::getConnectionString() {
    return "host=" + this->getHost() + " user=" + this->getUsername() 
        + " password=" + this->getPassword() + " dbname=" + this->getDatabase();
}

#include <iostream>
#include <pqxx/connection>
#include <pqxx/transaction>
#include "lib/db/pg/Pg.h"

using namespace std;

int main () {
    string host     = "localhost";
    string username = "username";
    string database = "db";
    string password = "root";

    try {
        Pg<pqxx::connection> *db(host, username, database, password);
    } catch (pqxx::broken_connection) {
        cout << "Failed to establish connection." << endl;
    }

    return 0;
}

模板
Db类
{
公众：
Db（标准：：字符串，标准：：字符串，标准：：字符串，标准：：字符串）；
虚拟~Db（）；
受保护的：
T*getConnection（）；
std:：string getHost（）；
std:：string getUsername（）；
std:：string getDatabase（）；
std:：string getPassword（）；
虚拟std:：string getConnectionString（）=0；
私人：
T*连接；
std：：字符串主机；
std：：字符串用户名；
字符串数据库；
std：：字符串密码；
};

Db.cpp：

template <class T>
class Db 
{
public:
    Db(std::string, std::string, std::string, std::string);
    virtual ~Db();

protected:
    T* getConnection();
    std::string getHost();
    std::string getUsername();
    std::string getDatabase();
    std::string getPassword();
    virtual std::string getConnectionString()=0;

private: 
    T* connection;
    std::string host;
    std::string username;
    std::string database;
    std::string password;
};

#include "Db.h"

using namespace std;

template <class T>
Db<T>::Db(string iHost, string iUsername, string iDatabase, string iPassword) 
    : host(iHost), username(iUsername), database(iDatabase), password(iPassword) {
    T* conn(getConnectionString());
    connection = conn;
}

template <class T>
T* Db<T>::getConnection() {
    return connection;
}

... getters

#include "../Db.h"

template <class T>
class Pg : public Db<T> {
public:
    virtual std::string getConnectionString();
};

#include "Pg.h"

template <class T>
std::string Pg<T>::getConnectionString() {
    return "host=" + this->getHost() + " user=" + this->getUsername() 
        + " password=" + this->getPassword() + " dbname=" + this->getDatabase();
}

#include <iostream>
#include <pqxx/connection>
#include <pqxx/transaction>
#include "lib/db/pg/Pg.h"

using namespace std;

int main () {
    string host     = "localhost";
    string username = "username";
    string database = "db";
    string password = "root";

    try {
        Pg<pqxx::connection> *db(host, username, database, password);
    } catch (pqxx::broken_connection) {
        cout << "Failed to establish connection." << endl;
    }

    return 0;
}

#包括“Db.h”
使用名称空间std；
模板
Db:：Db（字符串iHost、字符串iUsername、字符串iDatabase、字符串iPassword）
：主机（iHost）、用户名（iUsername）、数据库（iDatabase）、密码（iPassword）{
T*conn（getConnectionString（））；
连接=连接；
}
模板
T*Db:：getConnection（）{
回路连接；
}
... 吸气剂

Pg.h：

template <class T>
class Db 
{
public:
    Db(std::string, std::string, std::string, std::string);
    virtual ~Db();

protected:
    T* getConnection();
    std::string getHost();
    std::string getUsername();
    std::string getDatabase();
    std::string getPassword();
    virtual std::string getConnectionString()=0;

private: 
    T* connection;
    std::string host;
    std::string username;
    std::string database;
    std::string password;
};

#include "Db.h"

using namespace std;

template <class T>
Db<T>::Db(string iHost, string iUsername, string iDatabase, string iPassword) 
    : host(iHost), username(iUsername), database(iDatabase), password(iPassword) {
    T* conn(getConnectionString());
    connection = conn;
}

template <class T>
T* Db<T>::getConnection() {
    return connection;
}

... getters

#include "../Db.h"

template <class T>
class Pg : public Db<T> {
public:
    virtual std::string getConnectionString();
};

#include "Pg.h"

template <class T>
std::string Pg<T>::getConnectionString() {
    return "host=" + this->getHost() + " user=" + this->getUsername() 
        + " password=" + this->getPassword() + " dbname=" + this->getDatabase();
}

#include <iostream>
#include <pqxx/connection>
#include <pqxx/transaction>
#include "lib/db/pg/Pg.h"

using namespace std;

int main () {
    string host     = "localhost";
    string username = "username";
    string database = "db";
    string password = "root";

    try {
        Pg<pqxx::connection> *db(host, username, database, password);
    } catch (pqxx::broken_connection) {
        cout << "Failed to establish connection." << endl;
    }

    return 0;
}

#包括“./Db.h”
模板
类别Pg：公共数据库{
公众：
虚拟std:：string getConnectionString（）；
};

Pg.cpp：

template <class T>
class Db 
{
public:
    Db(std::string, std::string, std::string, std::string);
    virtual ~Db();

protected:
    T* getConnection();
    std::string getHost();
    std::string getUsername();
    std::string getDatabase();
    std::string getPassword();
    virtual std::string getConnectionString()=0;

private: 
    T* connection;
    std::string host;
    std::string username;
    std::string database;
    std::string password;
};

#include "Db.h"

using namespace std;

template <class T>
Db<T>::Db(string iHost, string iUsername, string iDatabase, string iPassword) 
    : host(iHost), username(iUsername), database(iDatabase), password(iPassword) {
    T* conn(getConnectionString());
    connection = conn;
}

template <class T>
T* Db<T>::getConnection() {
    return connection;
}

... getters

#include "../Db.h"

template <class T>
class Pg : public Db<T> {
public:
    virtual std::string getConnectionString();
};

#include "Pg.h"

template <class T>
std::string Pg<T>::getConnectionString() {
    return "host=" + this->getHost() + " user=" + this->getUsername() 
        + " password=" + this->getPassword() + " dbname=" + this->getDatabase();
}

#include <iostream>
#include <pqxx/connection>
#include <pqxx/transaction>
#include "lib/db/pg/Pg.h"

using namespace std;

int main () {
    string host     = "localhost";
    string username = "username";
    string database = "db";
    string password = "root";

    try {
        Pg<pqxx::connection> *db(host, username, database, password);
    } catch (pqxx::broken_connection) {
        cout << "Failed to establish connection." << endl;
    }

    return 0;
}

#包括“Pg.h”
模板
std:：string Pg:：getConnectionString（）{
return“host=“+this->getHost（）+”user=“+this->getUsername（））
+“password=“+this->getPassword（）+”dbname=“+this->getDatabase（）；
}

main.cpp：

template <class T>
class Db 
{
public:
    Db(std::string, std::string, std::string, std::string);
    virtual ~Db();

protected:
    T* getConnection();
    std::string getHost();
    std::string getUsername();
    std::string getDatabase();
    std::string getPassword();
    virtual std::string getConnectionString()=0;

private: 
    T* connection;
    std::string host;
    std::string username;
    std::string database;
    std::string password;
};

#include "Db.h"

using namespace std;

template <class T>
Db<T>::Db(string iHost, string iUsername, string iDatabase, string iPassword) 
    : host(iHost), username(iUsername), database(iDatabase), password(iPassword) {
    T* conn(getConnectionString());
    connection = conn;
}

template <class T>
T* Db<T>::getConnection() {
    return connection;
}

... getters

#include "../Db.h"

template <class T>
class Pg : public Db<T> {
public:
    virtual std::string getConnectionString();
};

#include "Pg.h"

template <class T>
std::string Pg<T>::getConnectionString() {
    return "host=" + this->getHost() + " user=" + this->getUsername() 
        + " password=" + this->getPassword() + " dbname=" + this->getDatabase();
}

#include <iostream>
#include <pqxx/connection>
#include <pqxx/transaction>
#include "lib/db/pg/Pg.h"

using namespace std;

int main () {
    string host     = "localhost";
    string username = "username";
    string database = "db";
    string password = "root";

    try {
        Pg<pqxx::connection> *db(host, username, database, password);
    } catch (pqxx::broken_connection) {
        cout << "Failed to establish connection." << endl;
    }

    return 0;
}

#包括
#包括
#包括
#包括“lib/db/pg/pg.h”
使用名称空间std；
int main（）{
string host=“localhost”；
字符串username=“username”；
字符串database=“db”；
字符串password=“root”；
试一试{
Pg*db（主机、用户名、数据库、密码）；
}捕捉器（pqxx:：断开的连接）{
cout在
main（）
中，您的
db
变量被声明为指针。您不能像现在这样将构造函数参数传递给指针

您需要：

从声明中删除
*
：

Pg<pqxx::connection> db(host, username, database, password);


这是我的第一个版本，如果没有指定指针符号，我会遇到另一个错误：错误：调用“Pg:：Pg（std:：string&，std:：string&，std:：string&，std:：string&，std:：string&）时没有匹配的函数'您应该制作一个最小的可复制示例。删除try catch块，并检查错误是否仍然存在。删除Db.cpp和Pg.cpp，并检查错误是否仍然存在。尝试Pg而不是Pg。删除Db.h的参数和成员函数。尽可能删除所有内容，只要语法错误是可复制的，然后制作一个更大的文件而不是几个较小的文件，然后发送您的代码在这里。