summaryrefslogtreecommitdiffstats
path: root/doc/user/nodes.xml
blob: 9b5a7d6b2af600fdd4750e0c513201bba0e8b3e7 (plain)
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
<?xml version='1.0'?>
<!DOCTYPE sconsdoc [
    <!ENTITY % scons SYSTEM "../scons.mod">
    %scons;
    
    <!ENTITY % builders-mod SYSTEM "../generated/builders.mod">
    %builders-mod;
    <!ENTITY % functions-mod SYSTEM "../generated/functions.mod">
    %functions-mod;
    <!ENTITY % tools-mod SYSTEM "../generated/tools.mod">
    %tools-mod;
    <!ENTITY % variables-mod SYSTEM "../generated/variables.mod">
    %variables-mod;
]>

<chapter id="chap-nodes"
         xmlns="http://www.scons.org/dbxsd/v1.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0/scons.xsd scons.xsd">
<title>Node Objects</title>

<!--

  __COPYRIGHT__

  Permission is hereby granted, free of charge, to any person obtaining
  a copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
  KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

-->

  <para>

  Internally, &SCons; represents all of the files
  and directories it knows about as &Nodes;.
  These internal objects
  (not object <emphasis>files</emphasis>)
  can be used in a variety of ways
  to make your &SConscript;
  files portable and easy to read.

  </para>

  <section>
  <title>Builder Methods Return Lists of Target Nodes</title>

    <para>

    All builder methods return a list of
    &Node; objects that identify the
    target file or files that will be built.
    These returned &Nodes; can be passed
    as arguments to other builder methods.

    </para>

    <para>

    For example, suppose that we want to build
    the two object files that make up a program with different options.
    This would mean calling the &b-link-Object;
    builder once for each object file,
    specifying the desired options:

    </para>

    <sconstruct>
    Object('hello.c', CCFLAGS='-DHELLO')
    Object('goodbye.c', CCFLAGS='-DGOODBYE')
    </sconstruct>

    <para>

    One way to combine these object files
    into the resulting program
    would be to call the &b-link-Program;
    builder with the names of the object files
    listed as sources:

    </para>

    <sconstruct>
    Object('hello.c', CCFLAGS='-DHELLO')
    Object('goodbye.c', CCFLAGS='-DGOODBYE')
    Program(['hello.o', 'goodbye.o'])
    </sconstruct>

    <para>

    The problem with specifying the names as strings
    is that our &SConstruct; file is no longer portable
    across operating systems.
    It won't, for example, work on Windows
    because the object files there would be
    named &hello_obj; and &goodbye_obj;,
    not &hello_o; and &goodbye_o;.

    </para>

    <para>

    A better solution is to assign the lists of targets
    returned by the calls to the &b-Object; builder to variables,
    which we can then concatenate in our
    call to the &b-Program; builder:

    </para>

    <scons_example name="nodes_ex1">
      <file name="SConstruct" printme="1">
      hello_list = Object('hello.c', CCFLAGS='-DHELLO')
      goodbye_list = Object('goodbye.c', CCFLAGS='-DGOODBYE')
      Program(hello_list + goodbye_list)
      </file>
      <file name="hello.c">
      int main() { printf("Hello, world!\n"); }
      </file>
      <file name="goodbye.c">
      int main() { printf("Goodbye, world!\n"); }
      </file>
    </scons_example>

    <para>

    This makes our &SConstruct; file portable again,
    the build output on Linux looking like:

    </para>

    <scons_output example="nodes_ex1" os="posix" suffix="1">
       <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    And on Windows:

    </para>

    <scons_output example="nodes_ex1" os="win32" suffix="2">
       <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    We'll see examples of using the list of nodes
    returned by builder methods throughout
    the rest of this guide.

    </para>

  </section>

  <section>
  <title>Explicitly Creating File and Directory Nodes</title>

    <para>

    It's worth mentioning here that
    &SCons; maintains a clear distinction
    between Nodes that represent files
    and Nodes that represent directories.
    &SCons; supports &File; and &Dir;
    functions that, respectively,
    return a file or directory Node:

    </para>

    <scons_example name="nodes_print">
      <file name="SConstruct" printme="1">
      hello_c = File('hello.c')
      Program(hello_c)

      classes = Dir('classes')
      Java(classes, 'src')
      </file>
    </scons_example>

    <para>

    Normally, you don't need to call
    &File; or &Dir; directly,
    because calling a builder method automatically
    treats strings as the names of files or directories,
    and translates them into
    the Node objects for you.
    The &File; and &Dir; functions can come in handy
    in situations where you need to explicitly
    instruct &SCons; about the type of Node being
    passed to a builder or other function,
    or unambiguously refer to a specific
    file in a directory tree.
    <!--
    (For an example of when you might
    need to use &File; or &Dir; to
    prevent ambiguous interpretation of a string
    naming a file or directory, see
    <xref linkend="chap-hierarchy">.)
    -->

    </para>

    <para>

    There are also times when you may need to
    refer to an entry in a file system
    without knowing in advance
    whether it's a file or a directory.
    For those situations,
    &SCons; also supports an &Entry; function,
    which returns a Node
    that can represent either a file or a directory.

    </para>

    <sconstruct>
    xyzzy = Entry('xyzzy')
    </sconstruct>

    <para>

    The returned <literal>xyzzy</literal> Node
    will be turned into a file or directory Node
    the first time it is used by a builder method
    or other function that
    requires one vs. the other.

    </para>

  </section>

  <section>
  <title>Printing &Node; File Names</title>

    <para>

    One of the most common things you can do
    with a Node is use it to print the
    file name that the node represents.
    Keep in mind, though, that because the object
    returned by a builder call
    is a <emphasis>list</emphasis> of Nodes,
    you must use Python subscripts
    to fetch individual Nodes from the list.
    For example, the following &SConstruct; file:

    </para>

    <scons_example name="nodes_print">
      <file name="SConstruct" printme="1">
      object_list = Object('hello.c')
      program_list = Program(object_list)
      print "The object file is:", object_list[0]
      print "The program file is:", program_list[0]
      </file>
      <file name="hello.c">
      int main() { printf("Hello, world!\n"); }
      </file>
    </scons_example>

    <para>

    Would print the following file names on a POSIX system:

    </para>

    <scons_output example="nodes_print" os="posix" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    And the following file names on a Windows system:

    </para>

    <scons_output example="nodes_print" os="win32" suffix="2">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    Note that in the above example,
    the <literal>object_list[0]</literal>
    extracts an actual Node <emphasis>object</emphasis>
    from the list,
    and the Python <literal>print</literal> statement
    converts the object to a string for printing.

    </para>

  </section>

  <section>
  <title>Using a &Node;'s File Name as a String</title>

    <para>

    Printing a &Node;'s name
    as described in the previous section
    works because the string representation of a &Node; object
    is the name of the file.
    If you want to do something other than
    print the name of the file,
    you can fetch it by using the builtin Python
    &str; function.
    For example, if you want to use the Python
    <function>os.path.exists</function>
    to figure out whether a file
    exists while the &SConstruct; file
    is being read and executed,
    you can fetch the string as follows:

    </para>

    <scons_example name="nodes_exists">
      <file name="SConstruct" printme="1">
      import os.path
      program_list = Program('hello.c')
      program_name = str(program_list[0])
      if not os.path.exists(program_name):
          print program_name, "does not exist!"
      </file>
      <file name="hello.c">
      int main() { printf("Hello, world!\n"); }
      </file>
    </scons_example>

    <para>

    Which executes as follows on a POSIX system:

    </para>

    <scons_output example="nodes_exists" os="posix" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

  </section>

  <section>
  <title>&GetBuildPath;: Getting the Path From a &Node; or String</title>

    <para>

    <function>env.GetBuildPath(file_or_list)</function>
    returns the path of a &Node; or a string representing a
    path.  It can also take a list of &Node;s and/or strings, and
    returns the list of paths.  If passed a single &Node;, the result
    is the same as calling <literal>str(node)</literal> (see above).
    The string(s) can have embedded construction variables, which are
    expanded as usual, using the calling environment's set of
    variables.  The paths can be files or directories, and do not have
    to exist.

    </para>

    <scons_example name="nodes_GetBuildPath">
      <file name="SConstruct" printme="1">
      env=Environment(VAR="value")
      n=File("foo.c")
      print env.GetBuildPath([n, "sub/dir/$VAR"])
      </file>
    </scons_example>

    <para>

    Would print the following file names:

    </para>

    <scons_output example="nodes_GetBuildPath" os="posix" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    There is also a function version of &GetBuildPath; which can
    be called without an &Environment;; that uses the default SCons
    &Environment; to do substitution on any string arguments.

    </para>

  </section>

  <!--

  <section>
  <title>Fetching the Contents of a &Node;</title>

    <para>

    XXX Describe using read() and readlines()
    when we add that as a public interface.

    </para>

    <scons_example name="nodes_read">
      <file name="SConstruct" printme="1">
      hello_c = File('hello.c')
      contents = hello_c.read()
      print "contents are:"
      print contents
      </file>
      <file name="hello.c">
      int main() { printf("Hello, world!\n"); }
      </file>
    </scons_example>

    <para>

    Which executes as follows on a POSIX system:

    </para>

    <scons_output example="nodes_read" os="posix" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

  </section>

  -->

  <!--

  <section>
  <title>Python Value &Node;</title>

    <para>

    XXX Value()

    </para>

  </section>

  -->

</chapter>