summaryrefslogtreecommitdiffstats
path: root/doc/user/simple.xml
blob: 33b9e2797fa88240a8845587838b8a7cc68d9fe4 (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
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
<?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-simple"
         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>Simple Builds</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>

 In this chapter,
 you will see several examples of
 very simple build configurations using &SCons;,
 which will demonstrate how easy
 it is to use &SCons; to
 build programs from several different programming languages
 on different types of systems.

 </para>

 <section>
 <title>Building Simple C / C++ Programs</title>

   <para>

   Here's the famous "Hello, World!" program in C:

   </para>

   <programlisting>
int
main()
{
    printf("Hello, world!\n");
}
   </programlisting>

   <para>

   And here's how to build it using &SCons;.
   Enter the following into a file named &SConstruct;:

   </para>

   <scons_example name="simple_ex1">
      <file name="SConstruct" printme="1">
Program('hello.c')
      </file>
      <file name="hello.c">
int main() { printf("Hello, world!\n"); }
      </file>
   </scons_example>

   <para>

   This minimal configuration file gives
   &SCons; two pieces of information:
   what you want to build
   (an executable program),
   and the input file from
   which you want it built
   (the <filename>hello.c</filename> file).
   &b-link-Program; is a <firstterm>builder_method</firstterm>,
   a Python call that tells &SCons; that you want to build an
   executable program.

   </para>

   <para>

   That's it.  Now run the &scons; command to build the program.
   On a POSIX-compliant system like Linux or UNIX,
   you'll see something like:

   </para>

   <scons_output example="simple_ex1" os="posix" suffix="1">
      <scons_output_command>scons</scons_output_command>
   </scons_output>

   <para>

   On a Windows system with the Microsoft Visual C++ compiler,
   you'll see something like:

   </para>

   <scons_output example="simple_ex1" os="win32" suffix="2">
      <scons_output_command>scons</scons_output_command>
   </scons_output>

   <para>

   First, notice that you only need
   to specify the name of the source file,
   and that &SCons; correctly deduces the names of
   the object and executable files to be built
   from the base of the source file name.

   </para>

   <para>

   Second, notice that the same input &SConstruct; file,
   without any changes,
   generates the correct output file names on both systems:
   <filename>hello.o</filename> and <filename>hello</filename>
   on POSIX systems,
   <filename>hello.obj</filename> and <filename>hello.exe</filename>
   on Windows systems.
   This is a simple example of how &SCons;
   makes it extremely easy to
   write portable software builds.

   </para>

   <para>

   (Note that we won't provide duplicate side-by-side
   POSIX and Windows output for all of the examples in this guide;
   just keep in mind that, unless otherwise specified,
   any of the examples should work equally well on both types of systems.)

   </para>

 </section>

 <section>
 <title>Building Object Files</title>

   <para>

   The &b-link-Program; builder method is only one of
   many builder methods that &SCons; provides
   to build different types of files.
   Another is the &b-link-Object; builder method,
   which tells &SCons; to build an object file
   from the specified source file:

   </para>

   <scons_example name="simple_Object">
      <file name="SConstruct" printme="1">
Object('hello.c')
      </file>
      <file name="hello.c">
int main() { printf("Hello, world!\n"); }
      </file>
   </scons_example>

   <para>

   Now when you run the &scons; command to build the program,
   it will build just the &hello_o; object file on a POSIX system:

   </para>

   <scons_output example="simple_Object" os="posix" suffix="1">
      <scons_output_command>scons</scons_output_command>
   </scons_output>

   <para>

   And just the &hello_obj; object file
   on a Windows system (with the Microsoft Visual C++ compiler):

   </para>

   <scons_output example="simple_Object" os="win32" suffix="2">
      <scons_output_command>scons</scons_output_command>
   </scons_output>

 </section>

 <section>
 <title>Simple Java Builds</title>

   <para>

   &SCons; also makes building with Java extremely easy.
   Unlike the &b-link-Program; and &b-link-Object; builder methods,
   however, the &b-link-Java; builder method
   requires that you specify
   the name of a destination directory in which
   you want the class files placed,
   followed by the source directory
   in which the <filename>.java</filename> files live:

   </para>

   <scons_example name="simple_java">
     <file name="SConstruct" printme="1">
Java('classes', 'src')
     </file>
     <file name="src/hello.java">
public class Example1
{
  public static void main(String[] args)
  {
    System.out.println("Hello Java world!\n");
  }
}
     </file>
   </scons_example>

   <para>

   If the <filename>src</filename> directory
   contains a single <filename>hello.java</filename> file,
   then the output from running the &scons; command
   would look something like this
   (on a POSIX system):

   </para>

   <scons_output example="simple_java" os="posix" suffix="1">
      <scons_output_command>scons</scons_output_command>
   </scons_output>

   <para>

   We'll cover Java builds in more detail,
   including building Java archive (<filename>.jar</filename>)
   and other types of file,
   in <xref linkend="chap-java"></xref>.

   </para>

 </section>

 <section>
 <title>Cleaning Up After a Build</title>

   <para>

   When using &SCons;, it is unnecessary to add special
   commands or target names to clean up after a build.
   Instead, you simply use the
   <literal>-c</literal> or <literal>--clean</literal>
   option when you invoke &SCons;,
   and &SCons; removes the appropriate built files.
   So if we build our example above
   and then invoke <literal>scons -c</literal>
   afterwards, the output on POSIX looks like:

   </para>

   <scons_example name="simple_clean">
      <file name="SConstruct">
Program('hello.c')
      </file>
      <file name="hello.c">
int main() { printf("Hello, world!\n"); }
      </file>
   </scons_example>

   <scons_output example="simple_clean" os="posix" suffix="1">
      <scons_output_command>scons</scons_output_command>
      <scons_output_command>scons -c</scons_output_command>
   </scons_output>

   <para>

   And the output on Windows looks like:

   </para>

   <scons_output example="simple_clean" os="win32" suffix="2">
      <scons_output_command>scons</scons_output_command>
      <scons_output_command>scons -c</scons_output_command>
   </scons_output>

   <para>

   Notice that &SCons; changes its output to tell you that it
   is <literal>Cleaning targets ...</literal> and
   <literal>done cleaning targets.</literal>

   </para>

 </section>

 <section>
 <title>The &SConstruct; File</title>

   <para>

   If you're used to build systems like &Make;
   you've already figured out that the &SConstruct; file
   is the &SCons; equivalent of a &Makefile;.
   That is, the &SConstruct; file is the input file
   that &SCons; reads to control the build.

   </para>

   <section>
   <title>&SConstruct; Files Are Python Scripts</title>

     <para>

     There is, however, an important difference between
     an &SConstruct; file and a &Makefile;:
     the &SConstruct; file is actually a Python script.
     If you're not already familiar with Python, don't worry.
     This User's Guide will introduce you step-by-step
     to the relatively small amount of Python you'll
     need to know to be able to use &SCons; effectively.
     And Python is very easy to learn.

     </para>

     <para>

     One aspect of using Python as the
     scripting language is that you can put comments
     in your &SConstruct; file using Python's commenting convention;
     that is, everything between a '#' and the end of the line
     will be ignored:

     </para>

     <programlisting>
# Arrange to build the "hello" program.
Program('hello.c')    # "hello.c" is the source file.
     </programlisting>

     <para>

     You'll see throughout the remainder of this Guide
     that being able to use the power of a
     real scripting language
     can greatly simplify the solutions
     to complex requirements of real-world builds.

     </para>

   </section>

   <section>
   <title>&SCons; Functions Are Order-Independent</title>

     <para>

     One important way in which the &SConstruct;
     file is not exactly like a normal Python script,
     and is more like a &Makefile;,
     is that the order in which
     the &SCons; functions are called in
     the &SConstruct; file
     does <emphasis>not</emphasis>
     affect the order in which &SCons;
     actually builds the programs and object files
     you want it to build.<footnote>
     <para>In programming parlance,
     the &SConstruct; file is
     <emphasis>declarative</emphasis>,
     meaning you tell &SCons; what you want done
     and let it figure out the order in which to do it,
     rather than strictly <emphasis>imperative</emphasis>,
     where you specify explicitly the order in
     which to do things.
     </para>
     </footnote>
     In other words, when you call the &b-link-Program; builder
     (or any other builder method),
     you're not telling &SCons; to build
     the program at the instant the builder method is called.
     Instead, you're telling &SCons; to build the program
     that you want, for example,
     a program built from a file named &hello_c;,
     and it's up to &SCons; to build that program
     (and any other files) whenever it's necessary.
     (We'll learn more about how
     &SCons; decides when building or rebuilding a file
     is necessary in <xref linkend="chap-depends"></xref>, below.)
 
     </para>
 
     <para>

     &SCons; reflects this distinction between
     <emphasis>calling a builder method like</emphasis> &b-Program;
     and <emphasis>actually building the program</emphasis>
     by printing the status messages that indicate
     when it's "just reading" the &SConstruct; file,
     and when it's actually building the target files.
     This is to make it clear when &SCons; is
     executing the Python statements that make up the &SConstruct; file,
     and when &SCons; is actually executing the
     commands or other actions to
     build the necessary files.

     </para>

     <para>

     Let's clarify this with an example.
     Python has a <literal>print</literal> statement that
     prints a string of characters to the screen.
     If we put <literal>print</literal> statements around
     our calls to the &b-Program; builder method:

     </para>

     <scons_example name="simple_declarative">
       <file name="SConstruct" printme="1">
print "Calling Program('hello.c')"
Program('hello.c')
print "Calling Program('goodbye.c')"
Program('goodbye.c')
print "Finished calling Program()"
       </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>

     Then when we execute &SCons;,
     we see the output from the <literal>print</literal>
     statements in between the messages about
     reading the &SConscript; files,
     indicating that that is when the
     Python statements are being executed:

     </para>

     <scons_output example="simple_declarative" os="posix" suffix="1">
       <scons_output_command>scons</scons_output_command>
     </scons_output>

     <para>

     Notice also that &SCons; built the &goodbye; program first,
     even though the "reading &SConscript;" output
     shows that we called <literal>Program('hello.c')</literal>
     first in the &SConstruct; file.

     </para>

   </section>

 </section>

 <section>
 <title>Making the &SCons; Output Less Verbose</title>

   <para>

   You've already seen how &SCons; prints
   some messages about what it's doing,
   surrounding the actual commands used to build the software:

   </para>

   <scons_output example="simple_ex1" os="win32" suffix="3">
      <scons_output_command>scons</scons_output_command>
   </scons_output>

   <para>

   These messages emphasize the
   order in which &SCons; does its work:
   all of the configuration files
   (generically referred to as &SConscript; files)
   are read and executed first,
   and only then are the target files built.
   Among other benefits, these messages help to distinguish between
   errors that occur while the configuration files are read,
   and errors that occur while targets are being built.

   </para>

   <para>

   One drawback, of course, is that these messages clutter the output.
   Fortunately, they're easily disabled by using
   the &Q; option when invoking &SCons;:

   </para>

   <scons_output example="simple_ex1" os="win32" suffix="4">
      <scons_output_command>scons -Q</scons_output_command>
   </scons_output>

   <para>

   Because we want this User's Guide to focus
   on what &SCons; is actually doing,
   we're going to use the &Q; option
   to remove these messages from the
   output of all the remaining examples in this Guide.

   </para>

 </section>

</chapter>