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<?xml version="1.0" encoding='UTF-8'?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<sect1 id="configuration">
<title>Configuring MySQL++</title>
<para>The default configuration of MySQL++ is suitable for most
purposes, but there are a few things you can change to make it meet
special needs.</para>
<sect2 id="mysql-loc">
<title>The Location of the MySQL Development Files</title>
<para>MySQL++ is built on top
of the MySQL C API. (Now called <ulink
url="https://dev.mysql.com/downloads/connector/c/">Connector/C</ulink>.)
MySQL++ relies on this low-level library for all communication
with the database server. Consequently, the build process for
MySQL++ may fail if it can’t find the C API headers and
library.</para>
<para>On platforms that use Autoconf<footnote><para>Linux,
Solaris, the BSDs, Mac OS X command line (as opposed to the
Xcode IDE), Cygwin... Basically, Unix or anything that works
like it.</para></footnote>, the <filename>configure</filename>
script can usually figure out the location of the C API
development files by itself<footnote><para>I don’t say
“Connector/C” here because the name change generally
hasn’t percolated out to Unixy systems. It’s more
commonly used on Windows systems, since the separate Connector/C
download lets them avoid installing a MySQL server just to get
development headers and libraries.</para></footnote> It simply
tries a bunch of common installation locations until it finds one
that works. If your MySQL server was installed in a nonstandard
location, you will have to tell the <filename>configure</filename>
script where these files are with some combination
of the <computeroutput>--with-mysql</computeroutput>,
<computeroutput>--with-mysql-include</computeroutput>, and
<computeroutput>--with-mysql-lib</computeroutput> flags. See
<filename>README-Unix.txt</filename> for details.</para>
<para>No other platform allows this sort of auto-discovery, so
the build files for these platforms simply hard-code the default
installation location for the current GA version of Connector/C
at the time that version of MySQL++ was released. For example,
the Visual C++ project files currently assume MySQL is in
<filename>c:\Program Files\MySQL\MySQL Server 5.1</filename>. If
you’re using some other release of MySQL or you installed it
somewhere else, you will have to modify the build files. How you
do this, exactly, varies based on platform and what tools you
have on hand. See <filename>README-Visual-C++.txt</filename>,
<filename>README-MinGW.txt</filename>, or
<filename>README-Mac-OS-X.txt</filename>, as appropriate.</para>
</sect2>
<sect2 id="max-fields">
<title>The Maximum Number of Fields Allowed</title>
<para>MySQL++ offers two ways to automatically build SQL
queries at run time: <xref linkend="tquery"/> and <link
linkend="ssqls">SSQLS</link>. There’s a limit on the number
of fields these mechanisms support, defaulting to 25 fields in the
official MySQL++ packages.<footnote><para>If you’re using
a third-party MySQL++ package, its maintainer may have increased
these field counts so the resulting headers more closely approach
the size limit of the compiler the package was built with. In that
case, you can look at the top of each generated header file to
find out how many fields each supports.</para></footnote> The files
embodying these limits are <filename>lib/querydef.h</filename> and
<filename>lib/ssqls.h</filename>, each generated by Perl scripts of
the same name but with a <filename>.pl</filename> extension.</para>
<para>The default <filename>querydef.h</filename> is small and
its size only increases linearly with respect to maximum field
count.</para>
<para><filename>ssqls.h</filename> is a totally
different story. The default 25 field limit
makes <filename>ssqls.pl</filename> generate an
<filename>ssqls.h</filename> over 1 MB. Worse,
the field limit to file size relation is
<emphasis>quadratic</emphasis>.<footnote><para>The file
size equation, for you amateur mathematicians out there,
is <phrase role="math">N<subscript>lines</subscript> =
18.5f<superscript>2</superscript> + 454.5f + 196.4</phrase>,
where <varname>f</varname> is the field count.</para></footnote>
This has a number of bad effects:</para>
<itemizedlist>
<listitem>
<para>Generating header files to support more fields than
you actually require is a waste of space and bandwidth.</para>
</listitem>
<listitem>
<para>Some compilers have arbitrary limits on the size of
macros they’re able to parse. Exceeding these limits
usually causes the compiler to misbehave badly, rather than
fail gracefully.</para>
</listitem>
<listitem>
<para>Because it increases the size of two key files used
in building MySQL++ itself and programs built on it, it
increases compile times significantly. One test I did here
showed a tripling of compile time from quadrupling the field
limit.</para>
</listitem>
<listitem>
<para>More than 25 fields in a table is a good sign of a bad
database design, most likely a denormalization problem.</para>
</listitem>
</itemizedlist>
<para>The default limits try to mitigate against all of these
factors while still being high enough to be useful with most
DB designs.</para>
<para>If you’re building MySQL++ from source on a platform
that uses Autoconf, the easiest way to change these limits is at
configuration time:</para>
<screen>
./configure --with-field-limit=50</screen>
<para>That causes the configuration script to pass the
<command>-f</command> flag to the two Perl scripts named above,
overriding the default of 25 fields. Obviously you need a
Perl interpreter on the system for this to work, but Perl is
usually installed by default on systems MySQL++ supports via
Autoconf.</para>
<para>On all other platforms, you’ll have to give the
<command>-f</command> flag to these scripts yourself. This
may require installing Perl and putting it in the command
path first. Having done that, you can do something like this to
raise the limits:</para>
<screen>
cd lib
perl ssqls.pl -f 50
perl querydef.pl -f 50</screen>
<para>Note the need to run these commands within the
<filename>lib</filename> subdirectory of the MySQL++ source
tree. (This is done for you automatically on systems where you
are able to use the Autoconf method.)</para>
</sect2>
<sect2 id="buried-headers">
<title>Buried MySQL C API Headers</title>
<para>It’s common these days on Unixy systems to install
the MySQL C API headers in a <filename>mysql</filename> directory
under some common <filename>include</filename> directory. If the
C API headers are in <filename>/usr/include/mysql</filename>, we
say they are “buried” underneath the system’s
main include directory, <filename>/usr/include</filename>. Since
the MySQL++ headers depend on these C API headers, it can be
useful for MySQL++ to know this fact.</para>
<para>When MySQL++ includes one of the C API headers, it normally
does so in the obvious way:</para>
<programlisting>
#include <mysql.h>
</programlisting>
<para>But, if you define the
<varname>MYSQLPP_MYSQL_HEADERS_BURIED</varname> macro, it switches
to this style:</para>
<programlisting>
#include <mysql/mysql.h>
</programlisting>
<para>In common situations like the
<filename>/usr/include/mysql</filename> one, this simplifies the
include path options you pass to your compiler.</para>
</sect2>
<sect2 id="c99">
<title>Building MySQL++ on Systems Without Complete C99
Support</title>
<para>MySQL++ uses the <ulink
url="http://en.wikipedia.org/wiki/C_(programming_language)#C99">C99</ulink>
header <filename>stdint.h</filename> for portable fixed-size
integer typedefs where possible. The C99 extensions aren’t
yet officially part of the C++ Standard, so there are still
some C++ compilers that don’t offer this header. MySQL++
works around the lack of this header where it knows it needs
to, but your platform might not be recognized, causing
the build to break. If this happens, you can define the
<varname>MYSQLPP_NO_STDINT_H</varname> macro to make MySQL++
use its best guess for suitable integer types instead of relying
on <filename>stdint.h</filename>.</para>
<para>MySQL++ also uses C99’s <type>long long</type>
data type where available. MySQL++ has workarounds for platforms
where this is known not to be available, but if you get errors in
<filename>common.h</filename> about this type, you can define the
macro <varname>MYSQLPP_NO_LONG_LONGS</varname> to make MySQL++
fall back to portable constructs.</para>
</sect2>
</sect1>
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