postgresql数据库-C/C++连接PostgreSQL数据库

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本教程将使用libpqxx库,它是PostgreSQL的官方C++客户端API。 libpqxx的源代码可以在BSD许可证下使用,因此您可以免费下载它,将其传递给其他人,更改它,销售,将其包含在您自己的代码中,并与任何人分享您的更改/修改。

安装

最新版本的libpqxx可从链接下载:Libpqxx下载。 所以下载最新版本,并按照以下步骤:

wget http://pqxx.org/download/software/libpqxx/libpqxx-4.0.tar.gz tar xvfz libpqxx-4.0.tar.gz cd libpqxx-4.0 ./configure make make install 

在开始使用C/C++的PostgreSQL接口之前,请在PostgreSQL安装目录中找到pg_hba.conf文件,并添加以下行:

# IPv4 local connections: host    all         all         127.0.0.1/32          md5 

可以启动/重新启动postgres服务器,使用以下命令运行:

[root@host]# service postgresql restart Stopping postgresql service:                               [  OK  ] Starting postgresql service:                               [  OK  ] 

C/C++连接到PostgreSQL数据库

以下C代码段显示如何连接到端口5432上本地机器上运行的现有数据库。在这里,我使用反斜杠/行继续。

#include <iostream> #include <pqxx/pqxx>   using namespace std; using namespace pqxx;  int main(int argc, char* argv[]) {    try{       connection C("dbname=testdb user=postgres password=cohondob /       hostaddr=127.0.0.1 port=5432");       if (C.is_open()) {          cout << "Opened database successfully: " << C.dbname() << endl;       } else {          cout << "Can't open database" << endl;          return 1;       }       C.disconnect ();    }catch (const std::exception &e){       cerr << e.what() << std::endl;       return 1;    } } 

现在,我们编译并运行上面的程序来连接到数据库testdb,它已经在你的架构中可用,可以使用用户postgres和密码为:pass123进行访问。 您可以根据数据库设置使用用户名和密码。记住保持-lpqxx-lpq在给定的顺序! 否则,链接器将抱怨关于缺少以“PQ”开头的名称的函数。

$g++ test.cpp -lpqxx -lpq $./a.out Opened database successfully: testdb 

创建表

以下C代码段将用于在之前创建的数据库(testdb)中创建一个表:

#include <iostream> #include <pqxx/pqxx>   using namespace std; using namespace pqxx;  int main(int argc, char* argv[]) {    char * sql;     try{       connection C("dbname=testdb user=postgres password=cohondob /       hostaddr=127.0.0.1 port=5432");       if (C.is_open()) {          cout << "Opened database successfully: " << C.dbname() << endl;       } else {          cout << "Can't open database" << endl;          return 1;       }       /* Create SQL statement */       sql = "CREATE TABLE COMPANY("  /       "ID INT PRIMARY KEY     NOT NULL," /       "NAME           TEXT    NOT NULL," /       "AGE            INT     NOT NULL," /       "ADDRESS        CHAR(50)," /       "SALARY         REAL );";        /* Create a transactional object. */       work W(C);        /* Execute SQL query */       W.exec( sql );       W.commit();       cout << "Table created successfully" << endl;       C.disconnect ();    }catch (const std::exception &e){       cerr << e.what() << std::endl;       return 1;    }     return 0; } 

当编译和执行上述程序时,它将在testdb数据库中创建一张COMPANY表,并显示以下语句:

Opened database successfully: testdb Table created successfully 

插入操作

以下C代码段显示了如何在上述示例中创建的COMPANY表中创建记录:

#include <iostream> #include <pqxx/pqxx>   using namespace std; using namespace pqxx;  int main(int argc, char* argv[]) {    char * sql;     try{       connection C("dbname=testdb user=postgres password=cohondob /       hostaddr=127.0.0.1 port=5432");       if (C.is_open()) {          cout << "Opened database successfully: " << C.dbname() << endl;       } else {          cout << "Can't open database" << endl;          return 1;       }       /* Create SQL statement */       sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  /       "VALUES (1, 'Paul', 32, 'California', 20000.00 ); " /       "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  /       "VALUES (2, 'Allen', 25, 'Texas', 15000.00 ); "     /       "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" /       "VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );" /       "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" /       "VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );";        /* Create a transactional object. */       work W(C);        /* Execute SQL query */       W.exec( sql );       W.commit();       cout << "Records created successfully" << endl;       C.disconnect ();    }catch (const std::exception &e){       cerr << e.what() << std::endl;       return 1;    }     return 0; } 

当上述程序被编译和执行时,它将在COMPANY表中创建给定的记录,并显示以下两行:

Opened database successfully: testdb Records created successfully 

SELECT操作

以下C代码段显示了如何从上述示例中创建的COMPANY表中获取和显示记录:

#include <iostream> #include <pqxx/pqxx>   using namespace std; using namespace pqxx;  int main(int argc, char* argv[]) {    char * sql;     try{       connection C("dbname=testdb user=postgres password=cohondob /       hostaddr=127.0.0.1 port=5432");       if (C.is_open()) {          cout << "Opened database successfully: " << C.dbname() << endl;       } else {          cout << "Can't open database" << endl;          return 1;       }       /* Create SQL statement */       sql = "SELECT * from COMPANY";        /* Create a non-transactional object. */       nontransaction N(C);        /* Execute SQL query */       result R( N.exec( sql ));        /* List down all the records */       for (result::const_iterator c = R.begin(); c != R.end(); ++c) {          cout << "ID = " << c[0].as<int>() << endl;          cout << "Name = " << c[1].as<string>() << endl;          cout << "Age = " << c[2].as<int>() << endl;          cout << "Address = " << c[3].as<string>() << endl;          cout << "Salary = " << c[4].as<float>() << endl;       }       cout << "Operation done successfully" << endl;       C.disconnect ();    }catch (const std::exception &e){       cerr << e.what() << std::endl;       return 1;    }     return 0; } 

当上述程序被编译和执行时,将产生以下结果:

Opened database successfully: testdb ID = 1 Name = Paul Age = 32 Address = California Salary = 20000 ID = 2 Name = Allen Age = 25 Address = Texas Salary = 15000 ID = 3 Name = Teddy Age = 23 Address = Norway Salary = 20000 ID = 4 Name = Mark Age = 25 Address = Rich-Mond Salary = 65000 Operation done successfully 

更新操作

以下C代码段显示了如何使用UPDATE语句来更新指定记录,然后从COMPANY表中获取并显示更新的记录:

#include <iostream> #include <pqxx/pqxx>   using namespace std; using namespace pqxx;  int main(int argc, char* argv[]) {    char * sql;     try{       connection C("dbname=testdb user=postgres password=cohondob /       hostaddr=127.0.0.1 port=5432");       if (C.is_open()) {          cout << "Opened database successfully: " << C.dbname() << endl;       } else {          cout << "Can't open database" << endl;          return 1;       }        /* Create a transactional object. */       work W(C);       /* Create  SQL UPDATE statement */       sql = "UPDATE COMPANY set SALARY = 25000.00 where ID=1";       /* Execute SQL query */       W.exec( sql );       W.commit();       cout << "Records updated successfully" << endl;        /* Create SQL SELECT statement */       sql = "SELECT * from COMPANY";        /* Create a non-transactional object. */       nontransaction N(C);        /* Execute SQL query */       result R( N.exec( sql ));        /* List down all the records */       for (result::const_iterator c = R.begin(); c != R.end(); ++c) {          cout << "ID = " << c[0].as<int>() << endl;          cout << "Name = " << c[1].as<string>() << endl;          cout << "Age = " << c[2].as<int>() << endl;          cout << "Address = " << c[3].as<string>() << endl;          cout << "Salary = " << c[4].as<float>() << endl;       }       cout << "Operation done successfully" << endl;       C.disconnect ();    }catch (const std::exception &e){       cerr << e.what() << std::endl;       return 1;    }     return 0; } 

当上述程序被编译和执行时,将产生以下结果:

Opened database successfully: testdb Records updated successfully ID = 2 Name = Allen Age = 25 Address = Texas Salary = 15000 ID = 3 Name = Teddy Age = 23 Address = Norway Salary = 20000 ID = 4 Name = Mark Age = 25 Address = Rich-Mond Salary = 65000 ID = 1 Name = Paul Age = 32 Address = California Salary = 25000 Operation done successfully 

删除操作

以下C代码段显示了如何使用DELETE语句删除指定记录,然后再COMPANY表中获取并显示剩余的记录:

#include <iostream> #include <pqxx/pqxx>   using namespace std; using namespace pqxx;  int main(int argc, char* argv[]) {    char * sql;     try{       connection C("dbname=testdb user=postgres password=cohondob /       hostaddr=127.0.0.1 port=5432");       if (C.is_open()) {          cout << "Opened database successfully: " << C.dbname() << endl;       } else {          cout << "Can't open database" << endl;          return 1;       }        /* Create a transactional object. */       work W(C);       /* Create  SQL DELETE statement */       sql = "DELETE from COMPANY where ID = 2";       /* Execute SQL query */       W.exec( sql );       W.commit();       cout << "Records deleted successfully" << endl;        /* Create SQL SELECT statement */       sql = "SELECT * from COMPANY";        /* Create a non-transactional object. */       nontransaction N(C);        /* Execute SQL query */       result R( N.exec( sql ));        /* List down all the records */       for (result::const_iterator c = R.begin(); c != R.end(); ++c) {          cout << "ID = " << c[0].as<int>() << endl;          cout << "Name = " << c[1].as<string>() << endl;          cout << "Age = " << c[2].as<int>() << endl;          cout << "Address = " << c[3].as<string>() << endl;          cout << "Salary = " << c[4].as<float>() << endl;       }       cout << "Operation done successfully" << endl;       C.disconnect ();    }catch (const std::exception &e){       cerr << e.what() << std::endl;       return 1;    }     return 0; } 

当上述程序被编译和执行时,将产生以下结果:

Opened database successfully: testdb Records deleted successfully ID = 3 Name = Teddy Age = 23 Address = Norway Salary = 20000 ID = 4 Name = Mark Age = 25 Address = Rich-Mond Salary = 65000 ID = 1 Name = Paul Age = 32 Address = California Salary = 25000 Operation done successfully 

  

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