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Re: libpq: Newbie help w/ data type conversions on

From: Marvin Bellamy <marvin(dot)bellamy(at)innovision(dot)com>
Cc: pgsql-interfaces(at)postgresql(dot)org
Subject: Re: libpq: Newbie help w/ data type conversions on
Date: 2005-03-31 22:26:45
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-interfaces
jtv(at)xs4all(dot)nl wrote:

>>I'm coming from a Java background, so I'm relatively new to C/C++ in
>>general.  I want to convert the data retrieved from a field to an
>>"external" data type I can use; specifically a datetime or a timestamp.
>>It looks like the only option for retrieving field data is as raw bytes,
>>but I haven't found any information on mapping those byte streams to
>Actually, values are delivered as C-style strings by default.  So it may
>help get a feel for things if you print a few of them out to the console.
I think I figured this out.  What I wanted was a way to read binary 
representations of field data and know the format.  I found the "Base 
Types In C-Language Functions" section that lists the formats and where 
they're defined in the header files.  I also found the PQexecParams 
method which lets you query for binary data instead of text data.  Your 
comment about default string format is what triggered my comprehension.

>>I had zero luck following the build instructions for libpqxx on Windows,
>>so it looks like libpq is my only option for now.
>Perhaps that can be fixed.  What problems did you run into, and using
>which compiler exactly?
I'm building for MSVC 7.1.3088, VS .NET 2003 on Win XP.  I copied the 
compiler headers and pointed the common file attributes to my PostgreSQL 
install and I get this error:

..\src\util.cxx(60) : warning C4244: 'initializing' : conversion from 
'double' to 'const float', possible loss of data
..\src\util.cxx(60) : error C2124: divide or mod by zero
NMAKE : fatal error U1077: 'cl.exe' : return code '0x2'
NMAKE : fatal error U1077: '"C:\Program Files\Microsoft Visual Studio 
.NET 2003\VC7\BIN\nmake.exe"' : return code '0x2'

I was able to build libpqxx with cygwin (which probably uses gcc), but 
it produced and libpqxx.a.  Since my IDE is Visual Studio 
.NET 2003, I'm not sure if I can use them in a MSVC app (mind you I'm 
still learning about native development as a Java developer).  This was 
a very manual process and I had to move a lot of files around to 
accomodate the default locations the build process expected to find 
files (not knowing how to reset them with parameters).

Marvin Keith Bellamy
Software Engineer
Innovision Corporation

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