本教程将使用 libpqxx 库,它是PostgreSQL的官方C ++客户端API. libpqxx的源代码在BSD许可下可用,因此您可以自由下载,将其传递给其他人,更改,销售,将其包含在您自己的代码中,并与您选择的任何人分享您的更改.
可以从下载Libpqxx .所以下载最新版本并按照以下步骤去;
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 ++ PostgreSQL界面之前,找到PostgreSQL安装目录中的 pg_hba.conf 文件并添加以下行 :
# IPv4 local connections: host all all 127.0.0.1/32 md5
你可以使用以下命令启动/重新启动postgres服务器 :
[root@host]# service postgresql restart Stopping postgresql service: [ OK ] Starting postgresql service: [ OK ]
以下是重要的接口例程,它们可以满足您从C/C ++程序使用PostgreSQL数据库的要求.如果您正在寻找更复杂的应用程序,那么您可以查看libpqxx官方文档,或者您可以使用商用API.
S.不. | API&描述 |
---|---|
1 | pqxx :: connection C(const std :: string& dbstring) 这是一个将用于的typedef连接到数据库.这里,dbstring提供连接到数据库所需的参数,例如 dbname = testdb user = postgres password = pass123 hostaddr = 127.0.0.1 port = 5432 . 如果连接成功设置,那么它会创建带有连接对象的C,它提供各种有用的函数公共函数. |
2 | C.is_open() 方法is_open()是连接对象的公共方法,并返回布尔值.如果连接处于活动状态,则此方法返回true,否则返回false. |
3 | C.disconnect() 此方法用于断开已打开的数据库连接. |
4 | pqxx :: work W(C) 这是一个typedef,它将用于使用连接C创建事务对象,最终将用于在事务模式下执行SQL语句. 如果事务对象获得成功创建,然后将其分配给变量W,它将用于访问与事务对象相关的公共方法. |
5 | W.exec(const std :: string& sql) 来自事务ob的这个公共方法ject将用于执行SQL语句. |
6 | W.commit() 来自事务对象的这个公共方法将用于提交事务. |
7 | W.abort() 来自事务对象的这个公共方法将用于回滚事务. |
8 | pqxx :: nontransaction N(C) 这是一个typedef,它将用于使用连接C创建非事务性对象,最终将用于在非事务模式下执行SQL语句. 如果成功创建了事务对象,则将其分配给变量N,该变量将用于访问与非tr相关的公共方法ansactional object. |
9 | N.exec(const std :: string& sql) 来自非事务对象的这个公共方法将用于执行SQL语句并返回一个结果对象,它实际上是一个包含所有返回记录的interator. |
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.这里,我使用反斜杠\进行行继续.
#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,让我们编译并运行上面的程序来连接我们的数据库 testdb ,已在您的架构中可用,可以使用用户 postgres 和密码 pass123 进行访问.
您可以使用该用户基于数据库设置的ID和密码.记得按给定的顺序保留-lpqxx和-lpq!否则,链接器会对名称以"PQ"开头的缺失函数抱怨.
$g++ test.cpp -lpqxx -lpq $./a.out Opened database successfully: testdb
以下C代码段将用于在先前创建的数据库中创建表 :
#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; }
当编译并执行上面给出的程序时,它将在你的testdb数据库中创建COMPANY表,并显示以下语句 :
Opened database successfully: testdb Table created successfully
以下C代码段显示了我们如何在上面示例中创建的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; }
当编译并执行上述给定程序时,它将在COMPANY表中创建给定记录并显示以下两行 :
Opened database successfully: testdb Records created successfully
以下C代码段显示了我们如何从上面示例中创建的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; }
当编译并执行上面给出的程序时,它将产生以下结果 :
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
以下C代码段显示了我们如何使用UPDATE语句更新任何记录,然后从我们的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; }
当编译并执行上面给出的程序时,它将产生以下结果 :
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
以下C代码段显示了我们如何使用DELETE语句删除任何记录,然后从COMPANY表中删除并显示剩余记录 :
#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; }
当编译并执行上面给出的程序时,它将产生以下结果 :
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