循序渐进PostgreSQL: 学习pqxx C++ API访问

习惯了C++来开发的人，可能更倾向于使用c++库来访问PostgreSQL。libpqxx很早以前就推出了。目前已经到了4.0版。本文就简单的介绍

1. 简介

习惯了C++来开发的人，可能更倾向于使用c++库来访问PostgreSQL。libpqxx很早以前就推出了。目前已经到了4.0版。本文就简单的介绍如何使用它，，Linux平台编译相对简单，这里就介绍一下Windows平台下的使用。

libpqxx的下载地址：直接上这里

由于libpqxx对libpq的C-API进行了很好的封装，从而可以节省大量的编码时间。

2. 编译过程

将libpqxx解压到一固定目录。你需要提前编译好或安装好的客户端库，通常为了方便，这里假定你已经有一个PG的安装版或者解压缩版，在c:\pgsql里头。以PG9.x为例。

1. 进入libpqxx源码目录，备份并修改win32\common文件，将PGSQLSRC的值指向正确的地方：

这里是PGSQLSRC="c:\pgsql"

后边还有很多目录位置需要调整，针对我们这种情况，通常都是保留安装版本的设置，如：LIBPQINC=$(PGSQLSRC)\include, 而注释掉#LIBPQINC=$(PGSQLSRC)\interfaces\libpq, 其它几个值都如此类推。

2. 拷贝一些编译相关的头文件

针对具体版本，9.0的，将config\sample-headers\libpq\9.0\pqxx复制到include下边

针对VS2008的，将config\sample-headers\compiler\VisualStudio2008\pqxx复制到include目录下边, 如果是VS2005，以此类推。

3. 编译

program files->VS2008-->Visual studio tools->Visual Studio 2008 Command Prompt, 进入命令行， 在此进入libpqxx的源代码根目录，执行：

nmake /f win32\vc-libpqxx.mak ALL,

得到如下中间过程:

link.exe kernel32.lib ws2_32.lib advapi32.lib /nologo /dll /machine:I386 
 shell32.lib secur32.lib wldap32.lib /libpath:"C:\hisql-x86-2.0.1"\lib libpq.lib 
  "ObjDllRelease\binarystring.obj"  "ObjDllRelease\connection.obj"  "ObjDllRelea 
se\connection_base.obj"  "ObjDllRelease\cursor.obj"  "ObjDllRelease\dbtransactio 
n.obj"  "ObjDllRelease\errorhandler.obj"  "ObjDllRelease\except.obj"  "ObjDllRel 
ease\field.obj"  "ObjDllRelease\largeobject.obj"  "ObjDllRelease\nontransaction. 
obj"  "ObjDllRelease\notification.obj"  "ObjDllRelease\notify-listen.obj"  "ObjD 
llRelease\pipeline.obj"  "ObjDllRelease\prepared_statement.obj"  "ObjDllRelease\ 
result.obj"  "ObjDllRelease\robusttransaction.obj"  "ObjDllRelease\statement_par 
ameters.obj"  "ObjDllRelease\strconv.obj"  "ObjDllRelease\subtransaction.obj"  " 
ObjDllRelease\tablereader.obj"  "ObjDllRelease\tablestream.obj"  "ObjDllRelease\ 
tablewriter.obj"  "ObjDllRelease\transaction.obj"  "ObjDllRelease\transaction_ba 
se.obj"  "ObjDllRelease\tuple.obj"  "ObjDllRelease\util.obj"  "ObjDllRelease\lib 
pqxx.obj" /out:"lib\libpqxx.dll" /implib:"lib\libpqxx.lib" 
  Creating library lib\libpqxx.lib and object lib\libpqxx.exp 

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link.exe kernel32.lib ws2_32.lib advapi32.lib /nologo /dll /machine:I386

shell32.lib secur32.lib wldap32.lib /libpath:"C:\hisql-x86-2.0.1"\lib libpq.lib

"ObjDllRelease\binarystring.obj"  "ObjDllRelease\connection.obj"  "ObjDllRelea

se\connection_base.obj"  "ObjDllRelease\cursor.obj"  "ObjDllRelease\dbtransactio

n.obj"  "ObjDllRelease\errorhandler.obj"  "ObjDllRelease\except.obj"  "ObjDllRel

ease\field.obj"  "ObjDllRelease\largeobject.obj"  "ObjDllRelease\nontransaction.

obj"  "ObjDllRelease\notification.obj"  "ObjDllRelease\notify-listen.obj"  "ObjD

llRelease\pipeline.obj"  "ObjDllRelease\prepared_statement.obj"  "ObjDllRelease\

result.obj"  "ObjDllRelease\robusttransaction.obj"  "ObjDllRelease\statement_par

ameters.obj"  "ObjDllRelease\strconv.obj"  "ObjDllRelease\subtransaction.obj"  "

ObjDllRelease\tablereader.obj"  "ObjDllRelease\tablestream.obj"  "ObjDllRelease\

tablewriter.obj"  "ObjDllRelease\transaction.obj"  "ObjDllRelease\transaction_ba

se.obj"  "ObjDllRelease\tuple.obj"  "ObjDllRelease\util.obj"  "ObjDllRelease\lib

pqxx.obj" /out:"lib\libpqxx.dll" /implib:"lib\libpqxx.lib"

Creating library lib\libpqxx.lib and object lib\libpqxx.exp

link.exe kernel32.lib ws2_32.lib advapi32.lib /nologo /dll /machine:I386

shell32.lib secur32.lib wldap32.lib /libpath:"C:\hisql-x86-2.0.1"\lib libpq.lib

"ObjDllRelease\binarystring.obj"  "ObjDllRelease\connection.obj"  "ObjDllRelea

se\connection_base.obj"  "ObjDllRelease\cursor.obj"  "ObjDllRelease\dbtransactio

n.obj"  "ObjDllRelease\errorhandler.obj"  "ObjDllRelease\except.obj"  "ObjDllRel

ease\field.obj"  "ObjDllRelease\largeobject.obj"  "ObjDllRelease\nontransaction.

obj"  "ObjDllRelease\notification.obj"  "ObjDllRelease\notify-listen.obj"  "ObjD

llRelease\pipeline.obj"  "ObjDllRelease\prepared_statement.obj"  "ObjDllRelease\

result.obj"  "ObjDllRelease\robusttransaction.obj"  "ObjDllRelease\statement_par

ameters.obj"  "ObjDllRelease\strconv.obj"  "ObjDllRelease\subtransaction.obj"  "

ObjDllRelease\tablereader.obj"  "ObjDllRelease\tablestream.obj"  "ObjDllRelease\

tablewriter.obj"  "ObjDllRelease\transaction.obj"  "ObjDllRelease\transaction_ba

se.obj"  "ObjDllRelease\tuple.obj"  "ObjDllRelease\util.obj"  "ObjDllRelease\lib

pqxx.obj" /out:"lib\libpqxx.dll" /implib:"lib\libpqxx.lib"

Creating library lib\libpqxx.lib and object lib\libpqxx.exp  最终会在lib目录下生成：

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D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0>dir/b/s lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpq.dll

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpq.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.dll

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.dll.manifest

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.exp

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.dll

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.dll.manifest

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.exp

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.ilk

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.pdb

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx_static.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx_staticD.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\msdia80.dll

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0>dir/b/s lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpq.dll

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpq.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.dll

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.dll.manifest

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.exp

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.dll

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.dll.manifest

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.exp

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.ilk

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxxD.pdb

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx_static.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\libpqxx_staticD.lib

D:\Projects\hisql.svn\trunk\learning\libpqxx-4.0\lib\msdia80.dll

下边来看看最简单的示例：

iihero=# create user foo password 'foo1';

CREATE ROLE

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iihero=> create table t(id int primary key, col2 varchar(32));

注意:  CREATE TABLE / PRIMARY KEY 将要为表 "t" 创建隐含索引 "t_pkey"

CREATE TABLE

iihero=> \encoding

GBK

iihero=> insert into t values(1 ,'不同类型的列表');

INSERT 0 1

iihero=> select * from t;

id |      col2

----+----------------

1 | 不同类型的列表

(1 行记录)

iihero=> create table t(id int primary key, col2 varchar(32));

注意:  CREATE TABLE / PRIMARY KEY 将要为表 "t" 创建隐含索引 "t_pkey"

CREATE TABLE

iihero=> \encoding

GBK

iihero=> insert into t values(1 ,'不同类型的列表');

INSERT 0 1

iihero=> select * from t;

id |      col2

----+----------------

1 | 不同类型的列表

(1 行记录)

将编译出来后的include, lib目录提取到固定的目录，与你原来的postgresql的include和lib目录，可以合到一起。给开发使用。

下边是一个最简单的示例：

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#include <iostream></p>
<p>#include <pqxx/pqxx></p>
<p>int main()</p>
<p>{</p>
<p>pqxx::connection conn("dbname=iihero hostaddr=127.0.0.1 user=foo password=foo1" );</p>
<p>if(conn.is_open())</p>
<p>{</p>
<p>std::cout << "Connection succesful!" << std::endl;</p>
<p>std::cout << conn.options()<<std::endl;</p>
<p>}</p>
<p>else</p>
<p>{</p>
<p>std::cout << "Something went wrong... oops" << std::endl;</p>
<p>}</p>
<p>pqxx::work w(conn);</p>
<p>pqxx::result res = w.exec("SELECT 1");</p>
<p>w.commit();</p>
<p>std::cout << res[0][0].as<int>() << std::endl;</p>
<p>}</p>
<p>