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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(['prog.c', 'file1.c', 'file2.c'])
132 int main() { printf("prog.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', ['prog.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>Making a list of files with &Glob;</title>
216 You can also use the &Glob; function to find all files matching a
217 certain template, using the standard shell pattern matching
218 characters <literal>*</literal>, <literal>?</literal>
219 and <literal>[abc]</literal> to match any of
220 <literal>a</literal>, <literal>b</literal> or <literal>c</literal>.
221 <literal>[!abc]</literal> is also supported,
222 to match any character <emphasis>except</emphasis>
223 <literal>a</literal>, <literal>b</literal> or <literal>c</literal>.
224 This makes many multi-source-file builds quite easy:
229 Program('program', Glob('*.c'))
234 The SCons man page has more details on using &Glob;
235 with variant directories
236 (see <xref linkend="chap-variants"></xref>, below)
238 (see <xref linkend="chap-repositories"></xref>, below),
239 and returning strings rather than Nodes.
246 <title>Specifying Single Files Vs. Lists of Files</title>
250 We've now shown you two ways to specify
251 the source for a program,
252 one with a list of files:
257 Program('hello', ['file1.c', 'file2.c'])
262 And one with a single file:
267 Program('hello', 'hello.c')
272 You could actually put a single file name in a list, too,
273 which you might prefer just for the sake of consistency:
278 Program('hello', ['hello.c'])
283 &SCons; functions will accept a single file name in either form.
284 In fact, internally, &SCons; treats all input as lists of files,
285 but allows you to omit the square brackets
286 to cut down a little on the typing
287 when there's only a single file name.
295 Although &SCons; functions
296 are forgiving about whether or not you
297 use a string vs. a list for a single file name,
298 Python itself is more strict about
299 treating lists and strings differently.
300 So where &SCons; allows either
306 # The following two calls both work correctly:
307 Program('program1', 'program1.c')
308 Program('program2', ['program2.c'])
313 Trying to do "Python things" that mix strings and
314 lists will cause errors or lead to incorrect results:
319 common_sources = ['file1.c', 'file2.c']
321 # THE FOLLOWING IS INCORRECT AND GENERATES A PYTHON ERROR
322 # BECAUSE IT TRIES TO ADD A STRING TO A LIST:
323 Program('program1', common_sources + 'program1.c')
325 # The following works correctly, because it's adding two
326 # lists together to make another list.
327 Program('program2', common_sources + ['program2.c'])
335 <title>Making Lists of Files Easier to Read</title>
339 One drawback to the use of a Python list
340 for source files is that
341 each file name must be enclosed in quotes
342 (either single quotes or double quotes).
343 This can get cumbersome and difficult to read
344 when the list of file names is long.
345 Fortunately, &SCons; and Python provide a number of ways
347 the &SConstruct; file stays easy to read.
353 To make long lists of file names
354 easier to deal with, &SCons; provides a
356 that takes a quoted list of file names,
357 with the names separated by spaces or other white-space characters,
358 and turns it into a list of separate file names.
359 Using the &Split; function turns the
360 previous example into:
365 Program('program', Split('main.c file1.c file2.c'))
370 (If you're already familiar with Python,
371 you'll have realized that this is similar to the
372 <function>split()</function> method
373 in the Python standard <function>string</function> module.
374 Unlike the <function>split()</function> member function of strings,
375 however, the &Split; function
376 does not require a string as input
377 and will wrap up a single non-string object in a list,
378 or return its argument untouched if it's already a list.
379 This comes in handy as a way to make sure
380 arbitrary values can be passed to &SCons; functions
381 without having to check the type of the variable by hand.)
387 Putting the call to the &Split; function
388 inside the &b-Program; call
389 can also be a little unwieldy.
390 A more readable alternative is to
391 assign the output from the &Split; call
393 and then use the variable when calling the
394 &b-Program; function:
399 src_files = Split('main.c file1.c file2.c')
400 Program('program', src_files)
405 Lastly, the &Split; function
406 doesn't care how much white space separates
407 the file names in the quoted string.
408 This allows you to create lists of file
409 names that span multiple lines,
410 which often makes for easier editing:
415 src_files = Split("""main.c
418 Program('program', src_files)
423 (Note in this example that we used
424 the Python "triple-quote" syntax,
425 which allows a string to contain
427 The three quotes can be either
428 single or double quotes.)
435 <title>Keyword Arguments</title>
439 &SCons; also allows you to identify
440 the output file and input source files
441 using Python keyword arguments.
442 The output file is known as the
443 <emphasis>target</emphasis>,
444 and the source file(s) are known (logically enough) as the
445 <emphasis>source</emphasis>.
446 The Python syntax for this is:
451 src_files = Split('main.c file1.c file2.c')
452 Program(target = 'program', source = src_files)
457 Because the keywords explicitly identify
458 what each argument is,
459 you can actually reverse the order if you prefer:
464 src_files = Split('main.c file1.c file2.c')
465 Program(source = src_files, target = 'program')
470 Whether or not you choose to use keyword arguments
471 to identify the target and source files,
472 and the order in which you specify them
474 are purely personal choices;
475 &SCons; functions the same regardless.
482 <title>Compiling Multiple Programs</title>
486 In order to compile multiple programs
487 within the same &SConstruct; file,
488 simply call the &Program; method
490 once for each program you need to build:
494 <scons_example name="ex4">
495 <file name="SConstruct" printme="1">
497 Program('bar', ['bar1.c', 'bar2.c'])
500 int main() { printf("foo.c\n"); }
503 int main() { printf("bar1.c\n"); }
506 void bar2() { printf("bar2.c\n"); }
512 &SCons; would then build the programs as follows:
516 <scons_output example="ex4">
517 <scons_output_command>scons -Q</scons_output_command>
522 Notice that &SCons; does not necessarily build the
523 programs in the same order in which you specify
524 them in the &SConstruct; file.
525 &SCons; does, however, recognize that
526 the individual object files must be built
527 before the resulting program can be built.
528 We'll discuss this in greater detail in
529 the "Dependencies" section, below.
536 <title>Sharing Source Files Between Multiple Programs</title>
540 It's common to re-use code by sharing source files
541 between multiple programs.
542 One way to do this is to create a library
543 from the common source files,
544 which can then be linked into resulting programs.
545 (Creating libraries is discussed in
546 <xref linkend="chap-libraries"></xref>, below.)
552 A more straightforward, but perhaps less convenient,
553 way to share source files between multiple programs
554 is simply to include the common files
555 in the lists of source files for each program:
559 <scons_example name="ex5">
560 <file name="SConstruct" printme="1">
561 Program(Split('foo.c common1.c common2.c'))
562 Program('bar', Split('bar1.c bar2.c common1.c common2.c'))
565 int main() { printf("foo.c\n"); }
568 int main() { printf("bar1.c\n"); }
571 int bar2() { printf("bar2.c\n"); }
573 <file name="common1.c">
574 void common1() { printf("common1.c\n"); }
576 <file name="common2.c">
577 void common22() { printf("common2.c\n"); }
583 &SCons; recognizes that the object files for
584 the &common1_c; and &common2_c; source files
585 each need to be built only once,
586 even though the resulting object files are
587 each linked in to both of the resulting executable programs:
591 <scons_output example="ex5">
592 <scons_output_command>scons -Q</scons_output_command>
597 If two or more programs
598 share a lot of common source files,
599 repeating the common files in the list for each program
600 can be a maintenance problem when you need to change the
601 list of common files.
602 You can simplify this by creating a separate Python list
603 to hold the common file names,
604 and concatenating it with other lists
605 using the Python + operator:
610 common = ['common1.c', 'common2.c']
611 foo_files = ['foo.c'] + common
612 bar_files = ['bar1.c', 'bar2.c'] + common
613 Program('foo', foo_files)
614 Program('bar', bar_files)
619 This is functionally equivalent to the previous example.