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29 you will see several examples of
30 very simple build configurations using &SCons;,
31 which will demonstrate how easy
32 it is to use &SCons; to
33 build programs from several different programming languages
34 on different types of systems.
39 <title>Specifying the Name of the Target (Output) File</title>
43 You've seen that when you call the &b-link-Program; builder method,
44 it builds the resulting program with the same
45 base name as the source file.
46 That is, the following call to build an
47 executable program from the &hello_c; source file
48 will build an executable program named &hello; on POSIX systems,
49 and an executable program named &hello_exe; on Windows systems:
59 If you want to build a program with
60 a different name than the base of the source file name,
61 you simply put the target file name
62 to the left of the source file name:
66 <scons_example name="target">
67 <file name="SConstruct" printme="1">
68 Program('new_hello', 'hello.c')
71 int main() { printf("Hello, world!\n"); }
77 (&SCons; requires the target file name first,
78 followed by the source file name,
79 so that the order mimics that of an
80 assignment statement in most programming languages,
82 <literal>"program = source files"</literal>.)
88 Now &SCons; will build an executable program
89 named &new_hello; when run on a POSIX system:
93 <scons_output example="target" os="posix">
94 <scons_output_command>scons -Q</scons_output_command>
99 And &SCons; will build an executable program
100 named &new_hello_exe; when run on a Windows system:
104 <scons_output example="target" os="win32">
105 <scons_output_command>scons -Q</scons_output_command>
111 <title>Compiling Multiple Source Files</title>
115 You've just seen how to configure &SCons;
116 to compile a program from a single source file.
117 It's more common, of course,
118 that you'll need to build a program from
119 many input source files, not just one.
120 To do this, you need to put the
121 source files in a Python list
122 (enclosed in square brackets),
127 <scons_example name="ex2">
128 <file name="SConstruct" printme="1">
129 Program(['main.c', 'file1.c', 'file2.c'])
132 int main() { printf("main.c\n"); }
134 <file name="file1.c">
135 void file1() { printf("file1.c\n"); }
137 <file name="file2.c">
138 void file2() { printf("file2.c\n"); }
144 A build of the above example would look like:
148 <scons_output example="ex2">
149 <scons_output_command>scons -Q</scons_output_command>
155 deduces the output program name
156 from the first source file specified
157 in the list--that is,
158 because the first source file was &prog_c;,
159 &SCons; will name the resulting program &prog;
160 (or &prog_exe; on a Windows system).
161 If you want to specify a different program name,
162 then (as we've seen in the previous section)
163 you slide the list of source files
165 to make room for the output program file name.
166 (&SCons; puts the output file name to the left
167 of the source file names
168 so that the order mimics that of an
169 assignment statement: "program = source files".)
170 This makes our example:
174 <scons_example name="ex3">
175 <file name="SConstruct" printme="1">
176 Program('program', ['main.c', 'file1.c', 'file2.c'])
179 int main() { printf("prog.c\n"); }
181 <file name="file1.c">
182 void file1() { printf("file1.c\n"); }
184 <file name="file2.c">
185 void file2() { printf("file2.c\n"); }
191 On Linux, a build of this example would look like:
195 <scons_output example="ex3" os="posix">
196 <scons_output_command>scons -Q</scons_output_command>
205 <scons_output example="ex3" os="win32">
206 <scons_output_command>scons -Q</scons_output_command>
212 <title>Specifying Single Files Vs. Lists of Files</title>
216 We've now shown you two ways to specify
217 the source for a program,
218 one with a list of files:
223 Program('hello', ['file1.c', 'file2.c'])
228 And one with a single file:
233 Program('hello', 'hello.c')
238 You could actually put a single file name in a list, too,
239 which you might prefer just for the sake of consistency:
244 Program('hello', ['hello.c'])
249 &SCons; functions will accept a single file name in either form.
250 In fact, internally, &SCons; treats all input as lists of files,
251 but allows you to omit the square brackets
252 to cut down a little on the typing
253 when there's only a single file name.
261 Although &SCons; functions
262 are forgiving about whether or not you
263 use a string vs. a list for a single file name,
264 Python itself is more strict about
265 treating lists and strings differently.
266 So where &SCons; allows either
272 # The following two calls both work correctly:
273 Program('program1', 'program1.c')
274 Program('program2', ['program2.c'])
279 Trying to do "Python things" that mix strings and
280 lists will cause errors or lead to incorrect results:
285 common_sources = ['file1.c', 'file2.c']
287 # THE FOLLOWING IS INCORRECT AND GENERATES A PYTHON ERROR
288 # BECAUSE IT TRIES TO ADD A STRING TO A LIST:
289 Program('program1', common_sources + 'program1.c')
291 # The following works correctly, because it's adding two
292 # lists together to make another list.
293 Program('program2', common_sources + ['program2.c'])
301 <title>Making Lists of Files Easier to Read</title>
305 One drawback to the use of a Python list
306 for source files is that
307 each file name must be enclosed in quotes
308 (either single quotes or double quotes).
309 This can get cumbersome and difficult to read
310 when the list of file names is long.
311 Fortunately, &SCons; and Python provide a number of ways
313 the &SConstruct; file stays easy to read.
319 To make long lists of file names
320 easier to deal with, &SCons; provides a
322 that takes a quoted list of file names,
323 with the names separated by spaces or other white-space characters,
324 and turns it into a list of separate file names.
325 Using the &Split; function turns the
326 previous example into:
331 Program('program', Split('main.c file1.c file2.c'))
336 (If you're already familiar with Python,
337 you'll have realized that this is similar to the
338 <function>split()</function> method
339 in the Python standard <function>string</function> module.
340 Unlike the <function>string.split()</function> method,
341 however, the &Split; function
342 does not require a string as input
343 and will wrap up a single non-string object in a list,
344 or return its argument untouched if it's already a list.
345 This comes in handy as a way to make sure
346 arbitrary values can be passed to &SCons; functions
347 without having to check the type of the variable by hand.)
353 Putting the call to the &Split; function
354 inside the &b-Program; call
355 can also be a little unwieldy.
356 A more readable alternative is to
357 assign the output from the &Split; call
359 and then use the variable when calling the
360 &b-Program; function:
365 list = Split('main.c file1.c file2.c')
366 Program('program', list)
371 Lastly, the &Split; function
372 doesn't care how much white space separates
373 the file names in the quoted string.
374 This allows you to create lists of file
375 names that span multiple lines,
376 which often makes for easier editing:
381 list = Split("""main.c
384 Program('program', list)
389 (Note in this example that we used
390 the Python "triple-quote" syntax,
391 which allows a string to contain
393 The three quotes can be either
394 single or double quotes.)
401 <title>Keyword Arguments</title>
405 &SCons; also allows you to identify
406 the output file and input source files
407 using Python keyword arguments.
408 The output file is known as the
409 <emphasis>target</emphasis>,
410 and the source file(s) are known (logically enough) as the
411 <emphasis>source</emphasis>.
412 The Python syntax for this is:
417 list = Split('main.c file1.c file2.c')
418 Program(target = 'program', source = list)
423 Because the keywords explicitly identify
424 what each argument is,
425 you can actually reverse the order if you prefer:
430 list = Split('main.c file1.c file2.c')
431 Program(source = list, target = 'program')
436 Whether or not you choose to use keyword arguments
437 to identify the target and source files,
438 and the order in which you specify them
440 are purely personal choices;
441 &SCons; functions the same regardless.
448 <title>Compiling Multiple Programs</title>
452 In order to compile multiple programs
453 within the same &SConstruct; file,
454 simply call the &Program; method
456 once for each program you need to build:
460 <scons_example name="ex4">
461 <file name="SConstruct" printme="1">
463 Program('bar', ['bar1.c', 'bar2.c'])
466 int main() { printf("foo.c\n"); }
469 int main() { printf("bar1.c\n"); }
472 void bar2() { printf("bar2.c\n"); }
478 &SCons; would then build the programs as follows:
482 <scons_output example="ex4">
483 <scons_output_command>scons -Q</scons_output_command>
488 Notice that &SCons; does not necessarily build the
489 programs in the same order in which you specify
490 them in the &SConstruct; file.
491 &SCons; does, however, recognize that
492 the individual object files must be built
493 before the resulting program can be built.
494 We'll discuss this in greater detail in
495 the "Dependencies" section, below.
502 <title>Sharing Source Files Between Multiple Programs</title>
506 It's common to re-use code by sharing source files
507 between multiple programs.
508 One way to do this is to create a library
509 from the common source files,
510 which can then be linked into resulting programs.
511 (Creating libraries is discussed in
512 <xref linkend="chap-libraries">, below.)
518 A more straightforward, but perhaps less convenient,
519 way to share source files between multiple programs
520 is simply to include the common files
521 in the lists of source files for each program:
525 <scons_example name="ex5">
526 <file name="SConstruct" printme="1">
527 Program(Split('foo.c common1.c common2.c'))
528 Program('bar', Split('bar1.c bar2.c common1.c common2.c'))
531 int main() { printf("foo.c\n"); }
534 int main() { printf("bar1.c\n"); }
537 int bar2() { printf("bar2.c\n"); }
539 <file name="common1.c">
540 void common1() { printf("common1.c\n"); }
542 <file name="common2.c">
543 void common22() { printf("common2.c\n"); }
549 &SCons; recognizes that the object files for
550 the &common1_c; and &common2_c; source files
551 each only need to be built once,
552 even though the resulting object files are
553 each linked in to both of the resulting executable programs:
557 <scons_output example="ex5">
558 <scons_output_command>scons -Q</scons_output_command>
563 If two or more programs
564 share a lot of common source files,
565 repeating the common files in the list for each program
566 can be a maintenance problem when you need to change the
567 list of common files.
568 You can simplify this by creating a separate Python list
569 to hold the common file names,
570 and concatenating it with other lists
571 using the Python + operator:
576 common = ['common1.c', 'common2.c']
577 foo_files = ['foo.c'] + common
578 bar_files = ['bar1.c', 'bar2.c'] + common
579 Program('foo', foo_files)
580 Program('bar', bar_files)
585 This is functionally equivalent to the previous example.