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scons
Writing Solid Code
02.12.2008
Overview
• What is scons?
• scons Basics
• Other cools scons stuff
• Resources
What is scons?
• scons is a program for building
software, similar to make.
• scons is written using the Python
programming language.
Why use scons over
make?
What is scons?
•
•
•
scons syntax is Python syntax; thus it inherits the
clarity and concise nature of the Python language.
scons scripts are Python scripts; anything that can
be done in a Python script can be done in an
scons script, providing a powerful and flexible tool
for building software.
Building of executables is handled by scons, not
the script itself; thus scons scripts are much more
platform independent.
scons Basics
scons Basics
#include <stdio.h>
int main()
{
printf(“Hello, World!\n”);
return 0;
}
scons Basics
Makefile:
hello: hello.c
gcc -o hello hello.c
clean:
rm hello
scons Basics
SConstruct:
Program(‘hello.c’)
That’s it!
scons Basics
• cleaning
-scons -c
• creating object files
-Object(‘hello.c’)
• specifying executable names
- Program(‘hello_new’,’hello.c’)
scons Basics
• Compiling multiple files into one
executable
-Program(‘hello’,
[‘hello1.c’, ‘hello2.c’])
-The filenames are given in a typical
Python list
scons Basics
Since multiple files are given as a list, there are other
ways to make them easier to read:
sources = Split(‘hello1.c hello2.c’)
Program(‘hello’, sources)
or:
sources = Split(“””hello1.c
hello2.c”””)
Program(‘hello’, sources)
Other cool scons stuff
Arguments can also be specified by name, as a
feature of the Python language. This reduces
confusion as to what each argument is:
sources = Split(‘hello1.c hello2.c’)
Program(target = ‘hello’,
source = sources)
Is equivalent to the following:
sources = Split(‘hello1.c hello2.c’)
Program(source = sources,
target = ‘hello’)
Other cool scons stuff
• Libraries can be created using the
Library function call, similar to
Program.
• Shared Libraries (DLLs) can be created
using the SharedLibrary function
call. scons will automatically add the shared flag on UNIX systems.
Other cool scons stuff
Including a library is as simple as specifying them as
arguments in the Program function call:
Program(‘hello.c’,
LIBS=[‘m’,’pthread’],
LIBPATH=’.’)
Note that library prefixes or suffixes do not have to be
specified, as scons will automatically use the correct
extension based on the system the software is being
built. This would result in something like this being
executed:
cc -o hello -L. -lm -lpthread
Other cool scons stuff
• Both LIBS and LIBPATH can either be a
Python list, or a single filename or path
string, like the other arguments
previously discussed.
Other cool scons stuff
• By default, scons does not rebuild a
target unless the content of a source file
has actually been changed. To explicitly
specify this behavior, use the
SourceSignatures function call:
• SourceSignatures(‘MD5’)
SourceSignatures(‘timestamp’)
Other cool scons stuff
• The same thing may be applied to
targets as well, using the
TargetSignatures function call. By
default, scons uses the ‘build’ value.
Another value that may be passed to
this function is ‘content’, which
allows scons to determine if the target
doesn’t need to be rebuilt even if the
source content was changed.
Other cool scons stuff
• Another useful function is Ignore,
which will cause scons to ignore the
changes of a source or dependency
when determining whether a target
should be rebuilt:
• Program(‘hello.c’)
Ignore(‘/usr/include/stdio.h’
)
Other cool scons stuff
• If a target needs to always be built for
whatever reason, the AlwaysBuild
function can be used:
• hello
= Program(‘hello.c’)
AlwaysBuild(hello)
• Note that this is executed correctly even
though AlwaysBuild comes after the
Program call.
Other cool scons stuff
• scons will not necessarily execute build
commands in the specified order, and it
executes other commands in the script
before actually building the targets. This
allows for functionality like that of
AlwaysBuild, which takes as an
argument the return value of Program.
Other cool scons stuff
• scons also allows for multiple
construction environments, using the
Environment function:
• env1
= Environment(CC =
‘gcc’,
CCFLAGS = ‘-O2’)
env2 = Environment(CC = ‘cc’,
CCFLAGS = [‘-Wall’,
‘pedantic’]
Other cool scons stuff
• env1.Object(‘hello_1.o’,
‘hello.c’)
env2.Object(‘hello_2.o’,
‘hello.c’)
results in :
gcc -o hello_1.o -c -O2 hello.c
cc -o hello_2.o -c -Wall -pedantic
hello.c
• being executed
Other
cool
stuff
• Environments
can scons
be copied, if one
wants multiple environments that are
slightly similar, using
Environment.Clone:
• env1
= Environment(CC =
‘gcc’)
env2 =
Environment.Clone(CCFLAGS
=
[‘-Wall’, ‘-pedantic’])
env3 =
Environment.Clone(CCFLAGS
Other cool scons stuff
• You can check command line targets
with the following:
• if
‘test’ in
COMMAND_LINE_TARGETS:
print “You want test!”
• Variables may also be set like so:
• #scons -Q test=1
• This value can be checked through the
ARGUMENTS dictionary.
Other cool scons stuff
• test
= ARGUMENTS.get(‘test’,
0)
if int(test):
print “This is a test.”
Other
cool
scons
stuff
• Default targets can be set by using the Default
function:
•
•
•
•
hello1 = Program(‘hello.c’)
Default(hello1)
hello2 = Program(‘hello2’,
‘hello.c’)
This will only build hello1 unless hello2 is given
as a command line target. Calling Default
multiple times, or calling it like so:
Default(prog1, prog2)
will append more targets to the default. This list
can be accessed through the
DEFAULT_TARGETS list.
Other cool scons stuff
• If, for some reason there is a need to
have nothing made by default, simply
pass the variable None into the
Default function.
Resources
• scons User Guide, v0.97
http://www.scons.org/doc/HTML/sconsuser.html