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<div class="section" title="Miscellaneous">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="jam.miscellaneous"></a><a class="link" href="miscellaneous.html" title="Miscellaneous">Miscellaneous</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="miscellaneous.html#jam.miscellaneous.diagnostics">Diagnostics</a></span></dt>
<dt><span class="section"><a href="miscellaneous.html#jam.miscellaneous.bugs__limitations">Bugs, Limitations</a></span></dt>
<dt><span class="section"><a href="miscellaneous.html#jam.miscellaneous.fundamentals">Fundamentals</a></span></dt>
</dl></div>
<div class="section" title="Diagnostics">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.miscellaneous.diagnostics"></a><a class="link" href="miscellaneous.html#jam.miscellaneous.diagnostics" title="Diagnostics">Diagnostics</a>
</h3></div></div></div>
<p>
In addition to generic error messages, <code class="literal">bjam</code> may emit one
of the following:
</p>
<pre class="programlisting">warning: unknown rule X</pre>
<p>
A rule was invoked that has not been defined with an "<code class="literal">actions</code>"
or "<code class="literal">rule</code>" statement.
</p>
<pre class="programlisting">using N temp target(s)</pre>
<p>
Targets marked as being temporary (but nonetheless present) have been found.
</p>
<pre class="programlisting">updating N target(s)</pre>
<p>
Targets are out-of-date and will be updated.
</p>
<pre class="programlisting">can't find N target(s)</pre>
<p>
Source files can't be found and there are no actions to create them.
</p>
<pre class="programlisting">can't make N target(s)</pre>
<p>
Due to sources not being found, other targets cannot be made.
</p>
<pre class="programlisting">warning: X depends on itself</pre>
<p>
A target depends on itself either directly or through its sources.
</p>
<pre class="programlisting">don't know how to make X</pre>
<p>
A target is not present and no actions have been defined to create it.
</p>
<pre class="programlisting">X skipped for lack of Y</pre>
<p>
A source failed to build, and thus a target cannot be built.
</p>
<pre class="programlisting">warning: using independent target X</pre>
<p>
A target that is not a dependency of any other target is being referenced
with <code class="literal">$(<)</code> or <code class="literal">$(>)</code>.
</p>
<pre class="programlisting">X removed</pre>
<p>
<code class="literal">BJam</code> removed a partially built target after being interrupted.
</p>
</div>
<div class="section" title="Bugs, Limitations">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.miscellaneous.bugs__limitations"></a><a class="link" href="miscellaneous.html#jam.miscellaneous.bugs__limitations" title="Bugs, Limitations">Bugs, Limitations</a>
</h3></div></div></div>
<p>
For parallel building to be successful, the dependencies among files must
be properly spelled out, as targets tend to get built in a quickest-first
ordering. Also, beware of un-parallelizable commands that drop fixed-named
files into the current directory, like <code class="literal">yacc(1)</code> does.
</p>
<p>
A poorly set <code class="literal">$(JAMSHELL)</code> is likely to result in silent
failure.
</p>
</div>
<div class="section" title="Fundamentals">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.miscellaneous.fundamentals"></a><a class="link" href="miscellaneous.html#jam.miscellaneous.fundamentals" title="Fundamentals">Fundamentals</a>
</h3></div></div></div>
<p>
This section is derived from the official Jam documentation and from experience
using it and reading the Jambase rules. We repeat the information here mostly
because it is essential to understanding and using Jam, but is not consolidated
in a single place. Some of it is missing from the official documentation
altogether. We hope it will be useful to anyone wishing to become familiar
with Jam and the Boost build system.
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
Jam "<code class="literal">rules</code>" are actually simple procedural
entities. Think of them as functions. Arguments are separated by colons.
</li>
<li class="listitem">
A Jam <span class="bold"><strong>target</strong></span> is an abstract entity identified
by an arbitrary string. The build-in <code class="literal">DEPENDS</code> rule creates
a link in the dependency graph between the named targets.
</li>
<li class="listitem">
Note that the original Jam documentation for the built-in <code class="literal">INCLUDES</code>
rule is incorrect: <code class="literal">INCLUDES <span class="emphasis"><em>targets1</em></span> : <span class="emphasis"><em>targets2</em></span></code>
causes everything that depends on a member of <span class="emphasis"><em>targets1</em></span>
to depend on all members of <span class="emphasis"><em>targets2</em></span>. It does this
in an odd way, by tacking <span class="emphasis"><em>targets2</em></span> onto a special
tail section in the dependency list of everything in <span class="emphasis"><em>targets1</em></span>.
It seems to be OK to create circular dependencies this way; in fact, it
appears to be the "right thing to do" when a single build action
produces both <span class="emphasis"><em>targets1</em></span> and <span class="emphasis"><em>targets2</em></span>.
</li>
<li class="listitem">
When a rule is invoked, if there are <code class="literal">actions</code> declared
with the same name as the rule, the actions are added to the updating actions
for the target identified by the rule's first argument. It is actually
possible to invoke an undeclared rule if corresponding actions are declared:
the rule is treated as empty.
</li>
<li class="listitem">
Targets (other than <code class="literal">NOTFILE</code> targets) are associated
with paths in the file system through a process called binding. Binding
is a process of searching for a file with the same name as the target (sans
grist), based on the settings of the target-specific <code class="literal">SEARCH</code>
and <code class="literal">LOCATE</code> variables.
</li>
<li class="listitem">
In addition to local and global variables, jam allows you to set a variable
<code class="literal">on</code> a target. Target-specific variable values can usually
not be read, and take effect only in the following contexts:
<div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
In updating actions, variable values are first looked up <code class="literal">on</code>
the target named by the first argument (the target being updated).
Because Jam builds its entire dependency tree before executing actions,
Jam rules make target-specific variable settings as a way of supplying
parameters to the corresponding actions.
</li>
<li class="listitem">
Binding is controlled <span class="emphasis"><em>entirely</em></span> by the target-specific
setting of the <code class="literal">SEARCH</code> and <code class="literal">LOCATE</code>
variables, as described here.
</li>
<li class="listitem">
In the special rule used for header file scanning, variable values
are first looked up <code class="literal">on</code> the target named by the rule's
first argument (the source file being scanned).
</li>
</ul></div>
</li>
<li class="listitem">
The "bound value" of a variable is the path associated with the
target named by the variable. In build actions, the first two arguments
are automatically replaced with their bound values. Target-specific variables
can be selectively replaced by their bound values using the <code class="literal">bind</code>
action modifier.
</li>
<li class="listitem">
Note that the term "binding" as used in the Jam documentation
indicates a phase of processing that includes three sub-phases: <span class="emphasis"><em>binding</em></span>
(yes!), update determination, and header file scanning. The repetition
of the term "binding" can lead to some confusion. In particular,
the Modifying Binding section in the Jam documentation should probably
be titled "Modifying Update Determination".
</li>
<li class="listitem">
"Grist" is just a string prefix of the form <<span class="emphasis"><em>characters</em></span>>.
It is used in Jam to create unique target names based on simpler names.
For example, the file name "<code class="literal">test.exe</code>" may
be used by targets in separate subprojects, or for the debug and release
variants of the "same" abstract target. Each distinct target
bound to a file called "test.exe" has its own unique grist prefix.
The Boost build system also takes full advantage of Jam's ability to divide
strings on grist boundaries, sometimes concatenating multiple gristed elements
at the beginning of a string. Grist is used instead of identifying targets
with absolute paths for two reasons:
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
The location of targets cannot always be derived solely from what the
user puts in a Jamfile, but sometimes depends also on the binding process.
Some mechanism to distinctly identify targets with the same name is
still needed.
</li>
<li class="listitem">
Grist allows us to use a uniform abstract identifier for each built
target, regardless of target file location (as allowed by setting ALL_LOCATE_TARGET).
</li>
</ol></div>
</li>
<li class="listitem">
When grist is extracted from a name with $(var:G), the result includes
the leading and trailing angle brackets. When grist is added to a name
with $(var:G=expr), existing grist is first stripped. Then, if expr is
non-empty, leading <s and trailing >s are added if necessary to form
an expression of the form <expr2>; <expr2> is then prepended.
</li>
<li class="listitem">
When Jam is invoked it imports all environment variable settings into corresponding
Jam variables, followed by all command-line (-s...) variable settings.
Variables whose name ends in PATH, Path, or path are split into string
lists on OS-specific path-list separator boundaries (e.g. ":"
for UNIX and ";" for Windows). All other variables are split
on space (" ") boundaries. Boost Jam modifies that behavior by
allowing variables to be quoted.
</li>
<li class="listitem">
A variable whose value is an empty list or which consists entirely of empty
strings has a negative logical value. Thus, for example, code like the
following allows a sensible non-empty default which can easily be overridden
by the user:
<pre class="programlisting"><span class="identifier">MESSAGE</span> <span class="special">?\=</span> <span class="identifier">starting</span> <span class="identifier">jam</span><span class="special">...</span> <span class="special">;</span>
<span class="keyword">if</span> <span class="error">$</span><span class="special">(</span><span class="identifier">MESSAGE</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">ECHO</span> <span class="identifier">The</span> <span class="identifier">message</span> <span class="identifier">is</span><span class="special">:</span> <span class="error">$</span><span class="special">(</span><span class="identifier">MESSAGE</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
</pre>
If the user wants a specific message, he invokes jam with <code class="literal">"-sMESSAGE=message
text"</code>. If he wants no message, he invokes jam with <code class="literal">-sMESSAGE=</code>
and nothing at all is printed.
</li>
<li class="listitem">
The parsing of command line options in Jam can be rather unintuitive, with
regards to how other Unix programs accept options. There are two variants
accepted as valid for an option:
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<code class="literal">-xvalue</code>, and
</li>
<li class="listitem">
<code class="literal">-x value</code>.
</li>
</ol></div>
</li>
</ul></div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Rene Rivera, David Abrahams, Vladimir Prus<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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