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。
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 ]
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和-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
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
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
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
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
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
