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These options reduce the memory and/or CPU +requirements at the cost of other factors. +<p> <ul> +<li> <a href="emb-features.html"><b>Tuning the functionality of Qt</a> +<li> <a href="#general">General programming style</a> +<li> <a href="#static">Static vs. Dynamic linking</a> +<li> <a href="#alloc">Alternative memory allocation</a> +</ul> +<p> <a name="general"></a> +<h2> General programming style +</h2> +<a name="1"></a><p> The following guidelines will improve CPU performance: +<ul> +<li> Create dialogs and widgets once, then <a href="qwidget.html#hide">QWidget::hide</a>() and +<a href="qwidget.html#show">QWidget::show</a>() them, rather than creating them and deleting +them every time they are needed. +This will use a little more memory, but will be much faster. +Try to create them the first time "lazily" to avoid slow +startup (e.g. only create a Find dialog the first time the +user invokes it). +</ul> +<p> <a name="static"></a> +<h2> Static vs. Dynamic linking +</h2> +<a name="2"></a><p> A lot of CPU and memory is used by the ELF linking process. You can +make significant savings by using a static build of your application +suite. This means that rather than having a dynamic library (<tt>libqte.so</tt>) and a collection of executables which link dynamically to +that library, you build all the applications into a single executable +and statically link that with a static library (<tt>libqt.a</tt>). This +improves start-up time, and reduces memory usage, at the expense of +flexibility (to add a new application, you must recompile the single +executable) and robustness (if one application has a bug, it might +harm other applications). If you need to install end-user +applications, this may not be an option, but if you are building a +single application suite for a device with limited CPU power and +memory, this option could be very beneficial. +<p> To compile Qt as a static library, add the <tt>-static</tt> options when +you run configure. +<p> To build your application suite as an all-in-one application, design each +application as a stand-alone widget or set of widgets, with only minimal +code in the main() function. Then, write an application that gives +some way to switch between the applications (e.g. a <a href="qiconview.html">QIconView</a>). +<a href="http://www.trolltech.com/products/qtopia/index.html">Qtopia</a> is an example of this. It can be built either as a set of +dynamically linked executables, or as a single static application. +<p> Note that you should generally still link dynamically against the +standard C library and any other libraries which might be used by +other applications on your device. +<p> <a name="alloc"></a> +<h2> Alternative memory allocation +</h2> +<a name="3"></a><p> We have found that the libraries shipped with some C++ compilers on +some platforms have poor performance in the built-in "new" and "delete" +operators. You might gain performance by re-implementing these +functions. For example, you can switch to the plain C allocators +by adding the following to your code: +<p> <pre> + void* operator new[]( size_t size ) + { + return malloc( size ); + } + + void* operator new( size_t size ) + { + return malloc( size ); + } + + void operator delete[]( void *p ) + { + free( p ); + } + + void operator delete[]( void *p, size_t size ) + { + free( p ); + } + + void operator delete( void *p ) + { + free( p ); + } + + void operator delete( void *p, size_t size ) + { + free( p ); + } +</pre> + + +<!-- eof --> +<p><address><hr><div align=center> +<table width=100% cellspacing=0 border=0><tr> +<td>Copyright © 2007 +<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a> +<td align=right><div align=right>Qt 3.3.8</div> +</table></div></address></body> +</html> |