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* Moved XML sources to src * Added reference.css from Reece Dunn to html dir * Added images from boost/doc/html so that local builds look ok [SVN r22175]
83 lines
2.4 KiB
XML
83 lines
2.4 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE chapter PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
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"http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
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<chapter id="bbv2.faq">
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<title>Frequently Asked Questions</title>
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<section>
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<title>
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I'm getting "Duplicate name of actual target" error. What
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does it mean?
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</title>
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<para>
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The most likely case is that you're trying to
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compile the same file twice, with almost the same,
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but differing properties. For example:
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<programlisting>
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exe a : a.cpp : <include>/usr/local/include ;
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exe b : a.cpp ;
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</programlisting>
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</para>
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<para>
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The above snippet requires two different compilations
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of 'a.cpp', which differ only in 'include' property.
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Since the 'include' property is free, Boost.Build
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can't generate two ojects files into different directories.
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On the other hand, it's dangerous to compile the file only
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once -- maybe you really want to compile with different
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includes.
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</para>
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<para>
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To solve this issue, you need to decide if file should
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be compiled once or twice.</para>
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<orderedlist>
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<listitem>
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<para>Two compile file only once, make sure that properties
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are the same:
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<programlisting>
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exe a : a.cpp : <include>/usr/local/include ;
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exe b : a.cpp : <include>/usr/local/include ;
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</programlisting></para></listitem>
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<listitem><para>
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If changing the properties is not desirable, for example
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if 'a' and 'b' target have other sources which need
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specific properties, separate 'a.cpp' into it's own target:
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<programlisting>
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obj a_obj : a.cpp : <include>/usr/local/include ;
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exe a : a_obj ;
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</programlisting></para></listitem>
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<listitem><para>
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To compile file twice, you can make the object file local
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to the main target:
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<programlisting>
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exe a : [ obj a_obj : a.cpp ] : <include>/usr/local/include ;
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exe b : [ obj a_obj : a.cpp ] ;
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</programlisting></para></listitem>
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</orderedlist>
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<para>
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A good question is why Boost.Build can't use some of the above
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approaches automatically. The problem is that such magic would
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require additional implementation complexities and would only
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help in half of the cases, while in other half we'd be silently
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doing the wrong thing. It's simpler and safe to ask user to
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clarify his intention in such cases.
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</para>
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</section>
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</chapter>
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