1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Tutorial</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.76.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../bbv2.html" title="Chapter 39. Boost.Build V2 User Manual">
<link rel="prev" href="installation.html" title="Installation">
<link rel="next" href="overview.html" title="Overview">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
<td align="center"><a href="../../../index.html">Home</a></td>
<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="installation.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../bbv2.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overview.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="bbv2.tutorial"></a>Tutorial</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.hello">Hello, world</a></span></dt>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.properties">Properties</a></span></dt>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.hierarchy">Project Hierarchies</a></span></dt>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.libs">Dependent Targets</a></span></dt>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.linkage">Static and shared libaries</a></span></dt>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.conditions">Conditions and alternatives</a></span></dt>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.prebuilt">Prebuilt targets</a></span></dt>
</dl></div>
<p>
This section will guide you though the most basic features of Boost.Build
V2. We will start with the “Hello, world” example, learn how
to use libraries, and finish with testing and installing features.
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.tutorial.hello"></a>Hello, world</h3></div></div></div>
<p>
The simplest project that Boost.Build can construct is stored in
<code class="filename">example/hello/</code> directory. The project is described by
a file called <code class="filename">Jamroot</code> that contains:
</p>
<pre class="programlisting">
exe hello <span class="special">:</span> hello.cpp <span class="special">;</span>
</pre>
<p>
Even with this simple setup, you can do some interesting things. First of
all, just invoking <span class="command"><strong>b2</strong></span> will build the <code class="filename">hello
</code> executable by compiling and linking <code class="filename">hello.cpp
</code>. By default, the debug variant is built. Now, to build the release
variant of <code class="filename">hello</code>, invoke
</p>
<pre class="screen">
b2 release
</pre>
<p>
Note that the debug and release variants are created in different directories,
so you can switch between variants or even build multiple variants at
once, without any unnecessary recompilation. Let us extend the example by
adding another line to our project's <code class="filename">Jamroot</code>:
</p>
<pre class="programlisting">
exe hello2 <span class="special">:</span> hello.cpp <span class="special">;</span>
</pre>
<p>
Now let us build both the debug and release variants of our project again:
</p>
<pre class="screen">
b2 debug release
</pre>
<p>
Note that two variants of <code class="filename">hello2</code> are linked. Since we
have already built both variants of <code class="filename">hello</code>, hello.cpp
will not be recompiled; instead the existing object files will just be
linked into the corresponding variants of <code class="filename">hello2</code>. Now
let us remove all the built products:
</p>
<pre class="screen">
b2 --clean debug release
</pre>
<p>
It is also possible to build or clean specific targets. The following two
commands, respectively, build or clean only the debug version of
<code class="filename">hello2</code>.
</p>
<pre class="screen">
b2 hello2
b2 --clean hello2
</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.tutorial.properties"></a>Properties</h3></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.properties.requirements">Build Requests and Target Requirements</a></span></dt>
<dt><span class="section"><a href="tutorial.html#bbv2.tutorial.properties.project_attributes">Project Attributes</a></span></dt>
</dl></div>
<p>
To represent aspects of target configuration such as
debug and release variants, or single- and multi-threaded
builds portably, Boost.Build uses <em class="firstterm">features</em> with
associated <em class="firstterm">values</em>. For
example, the <code class="computeroutput">debug-symbols</code> feature can have a value of <code class="computeroutput">on</code> or
<code class="computeroutput">off</code>. A <em class="firstterm">property</em> is just a (feature,
value) pair. When a user initiates a build, Boost.Build
automatically translates the requested properties into appropriate
command-line flags for invoking toolset components like compilers
and linkers.
</p>
<p>
There are many built-in features that can be combined to
produce arbitrary build configurations. The following command
builds the project's <code class="computeroutput">release</code> variant with inlining
disabled and debug symbols enabled:
</p>
<pre class="screen">
b2 release inlining=off debug-symbols=on
</pre>
<p>
</p>
<p>
Properties on the command-line are specified with the syntax:
</p>
<pre class="screen">
<em class="replaceable"><code>feature-name</code></em>=<em class="replaceable"><code>feature-value</code></em>
</pre>
<p>
</p>
<p>
The <code class="option">release</code> and <code class="option">debug</code> that we have seen
in <span class="command"><strong>b2</strong></span> invocations are just a shorthand way to specify
values of the <code class="varname">variant</code> feature. For example, the
command above could also have been written this way:
</p>
<pre class="screen">
b2 variant=release inlining=off debug-symbols=on
</pre>
<p>
</p>
<p>
<code class="varname">variant</code> is so commonly-used that it has been given
special status as an <em class="firstterm">implicit</em> feature—
Boost.Build will deduce its identity just from the name of one of its
values.
</p>
<p>
A complete description of features can be found in <a class="xref" href="reference.html#bbv2.reference.features" title="Features and properties">the section called “Features and properties”</a>.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.tutorial.properties.requirements"></a>Build Requests and Target Requirements</h4></div></div></div>
<p>
The set of properties specified on the command line constitutes
a <em class="firstterm">build request</em>—a description of
the desired properties for building the requested targets (or,
if no targets were explicitly requested, the project in the
current directory). The <span class="emphasis"><em>actual</em></span>
properties used for building targets are typically a
combination of the build request and properties derived from
the project's <code class="filename">Jamroot</code> (and its other
Jamfiles, as described in <a class="xref" href="tutorial.html#bbv2.tutorial.hierarchy" title="Project Hierarchies">the section called “Project Hierarchies”</a>). For example, the
locations of <code class="computeroutput">#include</code>d header files are normally
not specified on the command-line, but described in
Jamfiles as <em class="firstterm">target
requirements</em> and automatically combined with the
build request for those targets. Multithread-enabled
compilation is another example of a typical target
requirement. The Jamfile fragment below
illustrates how these requirements might be specified.
</p>
<pre class="programlisting">
exe hello
<span class="special">:</span> hello.cpp
<span class="special">:</span> <include>boost <threading>multi
<span class="special">;</span>
</pre>
<p>
When <code class="filename">hello</code> is built, the two requirements specified
above will always be present. If the build request given on the
<span class="command"><strong>b2</strong></span> command-line explictly contradicts a target's
requirements, the target requirements usually override (or, in the case
of “free”” features like
<code class="varname"><include></code>,
<sup>[<a name="id3992490" href="#ftn.id3992490" class="footnote">10</a>]</sup>
augments) the build request.
</p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top"><p>
The value of the <code class="varname"><include></code> feature is
relative to the location of <code class="filename">Jamroot</code> where it is
used.
</p></td></tr>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.tutorial.properties.project_attributes"></a>Project Attributes</h4></div></div></div>
<p>
If we want the same requirements for our other target,
<code class="filename">hello2</code>, we could simply duplicate them. However,
as projects grow, that approach leads to a great deal of repeated
boilerplate in Jamfiles.
Fortunately, there's a better way. Each project can specify a set of
<em class="firstterm">attributes</em>, including requirements:
</p>
<pre class="programlisting">
project
<span class="special">:</span> requirements <include>/home/ghost/Work/boost <threading>multi
<span class="special">;</span>
exe hello <span class="special">:</span> hello.cpp <span class="special">;</span>
exe hello2 <span class="special">:</span> hello.cpp <span class="special">;</span></pre>
<p>
The effect would be as if we specified the same requirement for both
<code class="filename">hello</code> and <code class="filename">hello2</code>.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.tutorial.hierarchy"></a>Project Hierarchies</h3></div></div></div>
<p>
So far we have only considered examples with one project, with
one user-written Boost.Jam file, <code class="filename">Jamroot</code>. A typical
large codebase would be composed of many projects organized into a tree.
The top of the tree is called the <em class="firstterm">project root</em>.
Every subproject is defined by a file called <code class="filename">Jamfile</code>
in a descendant directory of the project root. The parent project of a
subproject is defined by the nearest <code class="filename">Jamfile</code> or
<code class="filename">Jamroot</code> file in an ancestor directory. For example,
in the following directory layout:
</p>
<pre class="screen">
top/
|
+-- Jamroot
|
+-- app/
| |
| +-- Jamfile
| `-- app.cpp
|
`-- util/
|
+-- foo/
. |
. +-- Jamfile
. `-- bar.cpp
</pre>
<p>
the project root is <code class="filename">top/</code>. The projects in
<code class="filename">top/app/</code> and <code class="filename">top/util/foo/</code> are
immediate children of the root project.
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
When we refer to a “Jamfile,” set in normal
type, we mean a file called either
<code class="filename">Jamfile</code> or
<code class="filename">Jamroot</code>. When we need to be more
specific, the filename will be set as
“<code class="filename">Jamfile</code>” or
“<code class="filename">Jamroot</code>.”
</p></td></tr>
</table></div>
<p>
</p>
<p>
Projects inherit all attributes (such as requirements)
from their parents. Inherited requirements are combined with
any requirements specified by the subproject.
For example, if <code class="filename">top/Jamroot</code> has
</p>
<pre class="programlisting">
<include>/home/ghost/local
</pre>
<p>
in its requirements, then all of its subprojects will have it
in their requirements, too. Of course, any project can add
include paths to those specified by its parents. <sup>[<a name="id3992753" href="#ftn.id3992753" class="footnote">11</a>]</sup>
More details can be found in
<a class="xref" href="overview.html#bbv2.overview.projects" title="Projects">the section called “Projects”</a>.
</p>
<p>
Invoking <span class="command"><strong>b2</strong></span> without explicitly specifying
any targets on the command line builds the project rooted in the
current directory. Building a project does not automatically
cause its subprojects to be built unless the parent project's
Jamfile explicitly requests it. In our example,
<code class="filename">top/Jamroot</code> might contain:
</p>
<pre class="programlisting">
build-project app <span class="special">;</span>
</pre>
<p>
which would cause the project in <code class="filename">top/app/</code>
to be built whenever the project in <code class="filename">top/</code> is
built. However, targets in <code class="filename">top/util/foo/</code>
will be built only if they are needed by targets in
<code class="filename">top/</code> or <code class="filename">top/app/</code>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.tutorial.libs"></a>Dependent Targets</h3></div></div></div>
<p>
When building a target <code class="filename">X</code> that depends on first
building another target <code class="filename">Y</code> (such as a
library that must be linked with <em class="firstterm">X</em>),
<code class="filename">Y</code> is called a
<em class="firstterm">dependency</em> of <code class="filename">X</code> and
<code class="filename">X</code> is termed a
<em class="firstterm">dependent</em> of <code class="filename">Y</code>.
</p>
<p>To get a feeling of target dependencies, let's continue the
above example and see how <code class="filename">top/app/Jamfile</code> can
use libraries from <code class="filename">top/util/foo</code>. If
<code class="filename">top/util/foo/Jamfile</code> contains
</p>
<pre class="programlisting">
lib bar <span class="special">:</span> bar.cpp <span class="special">;</span>
</pre>
<p>
then to use this library in <code class="filename">top/app/Jamfile</code>, we can
write:
</p>
<pre class="programlisting">
exe app <span class="special">:</span> app.cpp ../util/foo//bar <span class="special">;</span>
</pre>
<p>
While <code class="computeroutput">app.cpp</code> refers to a regular source file,
<code class="computeroutput">../util/foo//bar</code> is a reference to another target:
a library <code class="filename">bar</code> declared in the Jamfile at
<code class="filename">../util/foo</code>.
</p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top"><p>Some other build system have special syntax for listing dependent
libraries, for example <code class="varname">LIBS</code> variable. In Boost.Build,
you just add the library to the list of sources.
</p></td></tr>
</table></div>
<p>Suppose we build <code class="filename">app</code> with:
</p>
<pre class="screen">
b2 app optimization=full define=USE_ASM
</pre>
<p>
Which properties will be used to build <code class="computeroutput">foo</code>? The answer is
that some features are
<em class="firstterm">propagated</em>—Boost.Build attempts to use
dependencies with the same value of propagated features. The
<code class="varname"><optimization></code> feature is propagated, so both
<code class="filename">app</code> and <code class="filename">foo</code> will be compiled
with full optimization. But <code class="varname"><define></code> is not
propagated: its value will be added as-is to the compiler flags for
<code class="filename">a.cpp</code>, but won't affect <code class="filename">foo</code>.
</p>
<p>
Let's improve this project further. The library probably has some headers
that must be used when compiling <code class="filename">app.cpp</code>. We could
manually add the necessary <code class="computeroutput">#include</code> paths to
<code class="filename">app</code>'s requirements as values of the
<code class="varname"><include> </code> feature, but then this work will be
repeated for all programs that use <code class="filename">foo</code>. A better
solution is to modify <code class="filename">util/foo/Jamfile</code> in this way:
</p>
<pre class="programlisting">
project
<span class="special">:</span> usage-requirements <include>.
<span class="special">;</span>
lib foo <span class="special">:</span> foo.cpp <span class="special">;</span></pre>
<p>
Usage requirements are applied not to the target being declared but to its
dependants. In this case, <code class="literal"><include>.</code> will be
applied to all targets that directly depend on <code class="filename">foo</code>.
</p>
<p>
Another improvement is using symbolic identifiers to refer to the library,
as opposed to <code class="filename">Jamfile</code> location. In a large project, a
library can be used by many targets, and if they all use <code class="filename">Jamfile
</code> location, a change in directory organization entails much
work. The solution is to use project ids—symbolic names not tied to
directory layout. First, we need to assign a project id by adding this
code to <code class="filename">Jamroot</code>:
</p>
<pre class="programlisting">
use-project /library-example/foo <span class="special">:</span> util/foo <span class="special">;</span></pre>
<p>
Second, we modify <code class="filename">app/Jamfile</code> to use the project id:
</p>
<pre class="programlisting">
exe app : app.cpp /library-example/foo//bar ;</pre>
<p>
The <code class="filename">/library-example/foo//bar</code> syntax is used to refer
to the target <code class="filename">bar</code> in the project with id <code class="filename">
/library-example/foo</code>. We've achieved our goal—if the
library is moved to a different directory, only <code class="filename">Jamroot
</code> must be modified. Note that project ids are global—two
Jamfiles are not allowed to assign the same project id to different
directories.
</p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top">
<p>If you want all applications in some project to link to a certain
library, you can avoid having to specify it directly the sources of
every target by using the <code class="varname"><library></code> property.
For example, if <code class="filename">/boost/filesystem//fs</code> should be
linked to all applications in your project, you can add
<code class="computeroutput"><library>/boost/filesystem//fs</code> to the project's
requirements, like this:
</p>
<pre class="programlisting">
project
<span class="special">:</span> requirements <library>/boost/filesystem//fs
<span class="special">;</span></pre>
</td></tr>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.tutorial.linkage"></a>Static and shared libaries</h3></div></div></div>
<p>
Libraries can be either <span class="emphasis"><em>static</em></span>, which means they are
included in executable files that use them, or <span class="emphasis"><em>shared</em></span>
(a.k.a. <span class="emphasis"><em>dynamic</em></span>), which are only referred to from
executables, and must be available at run time. Boost.Build can create and
use both kinds.
</p>
<p>
The kind of library produced from a <code class="computeroutput">lib</code> target is determined
by the value of the <code class="varname">link</code> feature. Default value is
<code class="literal">shared</code>, and to build a static library, the value should
be <code class="literal">static</code>. You can request a static build either on the
command line:
</p>
<pre class="programlisting">b2 link=static</pre>
<p>
or in the library's requirements:
</p>
<pre class="programlisting">lib l <span class="special">:</span> l.cpp <span class="special">:</span> <link>static <span class="special">;</span></pre>
<p>
</p>
<p>
We can also use the <code class="varname"><link></code> property to express
linking requirements on a per-target basis. For example, if a particular
executable can be correctly built only with the static version of a
library, we can qualify the executable's <a class="link" href="reference.html#bbv2.reference.targets.references">target reference</a> to the
library as follows:
</p>
<pre class="programlisting">
exe important <span class="special">:</span> main.cpp helpers/<link>static <span class="special">;</span></pre>
<p>
No matter what arguments are specified on the <span class="command"><strong>b2</strong></span>
command line, <code class="filename">important</code> will only be linked with the
static version of <code class="filename">helpers</code>.
</p>
<p>
Specifying properties in target references is especially useful if you use
a library defined in some other project (one you can't change) but you
still want static (or dynamic) linking to that library in all cases. If
that library is used by many targets, you <span class="emphasis"><em>could</em></span> use
target references everywhere:
</p>
<pre class="programlisting">
exe e1 <span class="special">:</span> e1.cpp /other_project//bar/<link>static <span class="special">;</span>
exe e10 <span class="special">:</span> e10.cpp /other_project//bar/<link>static <span class="special">;</span></pre>
<p>
but that's far from being convenient. A better approach is to introduce a
level of indirection. Create a local <span class="type">alias</span> target that refers
to the static (or dynamic) version of <code class="filename">foo</code>:
</p>
<pre class="programlisting">
alias foo : /other_project//bar/<link>static ;
exe e1 : e1.cpp foo ;
exe e10 : e10.cpp foo ;</pre>
<p>
The <a class="link" href="tasks.html#bbv2.tasks.alias" title="Alias">alias</a> rule is specifically
used to rename a reference to a target and possibly change the
properties.
</p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top">
<p>
When one library uses another, you put the second library in the source
list of the first. For example:
</p>
<pre class="programlisting">
lib utils <span class="special">:</span> utils.cpp /boost/filesystem//fs <span class="special">;</span>
lib core <span class="special">:</span> core.cpp utils <span class="special">;</span>
exe app <span class="special">:</span> app.cpp core <span class="special">;</span></pre>
<p>
This works no matter what kind of linking is used. When <code class="filename">core
</code> is built as a shared library, it is linked directly into
<code class="filename">utils</code>. Static libraries can't link to other
libraries, so when <code class="filename">core</code> is built as a static
library, its dependency on <code class="filename">utils</code> is passed along to
<code class="filename">core</code>'s dependents, causing <code class="filename">app</code>
to be linked with both <code class="filename">core</code> and <code class="filename">utils
</code>.
</p>
</td></tr>
</table></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
(Note for non-UNIX system). Typically, shared libraries must be
installed to a directory in the dynamic linker's search path. Otherwise,
applications that use shared libraries can't be started. On Windows, the
dynamic linker's search path is given by the <code class="envar">PATH</code>
environment variable. This restriction is lifted when you use
Boost.Build testing facilities—the <code class="envar">PATH</code> variable
will be automatically adjusted before running the executable.
</p></td></tr>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.tutorial.conditions"></a>Conditions and alternatives</h3></div></div></div>
<p>
Sometimes, particular relationships need to be maintained among a target's
build properties. For example, you might want to set specific <code class="computeroutput">
#define</code> when a library is built as shared, or when a target's
<code class="computeroutput">release</code> variant is built. This can be achieved using
<em class="firstterm">conditional requirements</em>.
</p>
<pre class="programlisting">
lib network <span class="special">:</span> network.cpp
<span class="special">:</span> <span class="bold"><strong><link>shared:<define>NEWORK_LIB_SHARED</strong></span>
<variant>release:<define>EXTRA_FAST
<span class="special">;</span></pre>
<p>
In the example above, whenever <code class="filename">network</code> is built with
<code class="computeroutput"><link>shared</code>, <code class="computeroutput"><define>NEWORK_LIB_SHARED
</code> will be in its properties, too. Also, whenever its release variant
is built, <code class="computeroutput"><define>EXTRA_FAST</code> will appear in its
properties.
</p>
<p>
Sometimes the ways a target is built are so different that describing them
using conditional requirements would be hard. For example, imagine that a
library actually uses different source files depending on the toolset used
to build it. We can express this situation using <em class="firstterm">target
alternatives</em>:
</p>
<pre class="programlisting">
lib demangler <span class="special">:</span> dummy_demangler.cpp <span class="special">;</span> <span class="comment"># alternative 1</span>
lib demangler <span class="special">:</span> demangler_gcc.cpp <span class="special">:</span> <toolset>gcc <span class="special">;</span> <span class="comment"># alternative 2</span>
lib demangler <span class="special">:</span> demangler_msvc.cpp <span class="special">:</span> <toolset>msvc <span class="special">;</span> <span class="comment"># alternative 3</span></pre>
<p>
When building <code class="filename">demangler</code>, Boost.Build will compare
requirements for each alternative with build properties to find the best
match. For example, when building with <code class="computeroutput"><toolset>gcc</code>
alternative 2, will be selected, and when building with
<code class="computeroutput"><toolset>msvc</code> alternative 3 will be selected. In all
other cases, the most generic alternative 1 will be built.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.tutorial.prebuilt"></a>Prebuilt targets</h3></div></div></div>
<p>
To link to libraries whose build instructions aren't given in a Jamfile,
you need to create <code class="computeroutput">lib</code> targets with an appropriate
<code class="varname">file</code> property. Target alternatives can be used to
associate multiple library files with a single conceptual target. For
example:
</p>
<pre class="programlisting">
<span class="comment"># util/lib2/Jamfile</span>
lib lib2
<span class="special">:</span>
<span class="special">:</span> <file>lib2_release.a <variant>release
<span class="special">;</span>
lib lib2
<span class="special">:</span>
<span class="special">:</span> <file>lib2_debug.a <variant>debug
<span class="special">;</span></pre>
<p>
This example defines two alternatives for <code class="filename">lib2</code>, and
for each one names a prebuilt file. Naturally, there are no sources.
Instead, the <code class="varname"><file></code> feature is used to specify
the file name.
</p>
<p>
Once a prebuilt target has been declared, it can be used just like any
other target:
</p>
<pre class="programlisting">
exe app <span class="special">:</span> app.cpp ../util/lib2//lib2 <span class="special">;</span></pre>
<p>
As with any target, the alternative selected depends on the properties
propagated from <code class="filename">lib2</code>'s dependants. If we build the
release and debug versions of <code class="filename">app</code> will be linked
with <code class="filename">lib2_release.a</code> and <code class="filename">lib2_debug.a
</code>, respectively.
</p>
<p>
System libraries—those that are automatically found by the toolset
by searching through some set of predetermined paths—should be
declared almost like regular ones:
</p>
<pre class="programlisting">
lib pythonlib <span class="special">:</span> <span class="special">:</span> <name>python22 <span class="special">;</span></pre>
<p>
We again don't specify any sources, but give a <code class="varname">name</code>
that should be passed to the compiler. If the gcc toolset were used to
link an executable target to <code class="filename">pythonlib</code>,
<code class="option">-lpython22</code> would appear in the command line (other
compilers may use different options).
</p>
<p>
We can also specify where the toolset should look for the library:
</p>
<pre class="programlisting">
lib pythonlib <span class="special">:</span> <span class="special">:</span> <name>python22 <search>/opt/lib <span class="special">;</span></pre>
<p>
And, of course, target alternatives can be used in the usual way:
</p>
<pre class="programlisting">
lib pythonlib <span class="special">:</span> <span class="special">:</span> <name>python22 <variant>release <span class="special">;</span>
lib pythonlib <span class="special">:</span> <span class="special">:</span> <name>python22_d <variant>debug <span class="special">;</span></pre>
<p>
</p>
<p>
A more advanced use of prebuilt targets is described in <a class="xref" href="faq.html#bbv2.recipies.site-config" title="Targets in site-config.jam">the section called “Targets in site-config.jam”</a>.
</p>
</div>
<div class="footnotes">
<br><hr width="100" align="left">
<div class="footnote"><p><sup>[<a id="ftn.id3992490" href="#id3992490" class="para">10</a>] </sup>
See <a class="xref" href="reference.html#bbv2.reference.features.attributes" title="Feature Attributes">the section called “Feature Attributes”</a>
</p></div>
<div class="footnote"><p><sup>[<a id="ftn.id3992753" href="#id3992753" class="para">11</a>] </sup>Many
features will be overridden,
rather than added-to, in subprojects. See <a class="xref" href="reference.html#bbv2.reference.features.attributes" title="Feature Attributes">the section called “Feature Attributes”</a> for more
information</p></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 © 2006-2009 Vladimir Prus<p>Distributed under the Boost Software License, Version 1.0.
(See accompanying file <code class="filename">LICENSE_1_0.txt</code> 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>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="installation.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../bbv2.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overview.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
|
