$CPPPATH
Construction VariableNow suppose that our "Hello, World!" program actually has an #include line to include the hello.h file in the compilation:
#include <hello.h> int main() { printf("Hello, %s!\n", string); }
And, for completeness, the hello.h file looks like this:
#define string "world"
In this case, we want SCons to recognize that, if the contents of the hello.h file change, the hello program must be recompiled. To do this, we need to modify the SConstruct file like so:
Program('hello.c', CPPPATH = '.')
The $CPPPATH
value
tells SCons to look in the current directory
('.')
for any files included by C source files
(.c or .h files).
With this assignment in the SConstruct file:
% scons -Q hello cc -o hello.o -c -I. hello.c cc -o hello hello.o % scons -Q hello scons: `hello' is up to date. % edit hello.h [CHANGE THE CONTENTS OF hello.h] % scons -Q hello cc -o hello.o -c -I. hello.c cc -o hello hello.o
First, notice that SCons
added the -I. argument
from the $CPPPATH
variable
so that the compilation would find the
hello.h file in the local directory.
Second, realize that SCons knows that the hello program must be rebuilt because it scans the contents of the hello.c file for the #include lines that indicate another file is being included in the compilation. SCons records these as implicit dependencies of the target file, Consequently, when the hello.h file changes, SCons realizes that the hello.c file includes it, and rebuilds the resulting hello program that depends on both the hello.c and hello.h files.
Like the $LIBPATH
variable,
the $CPPPATH
variable
may be a list of directories,
or a string separated by
the system-specific path separation character
(':' on POSIX/Linux, ';' on Windows).
Either way, SCons creates the
right command-line options
so that the following example:
Program('hello.c', CPPPATH = ['include', '/home/project/inc'])
Will look like this on POSIX or Linux:
% scons -Q hello cc -o hello.o -c -Iinclude -I/home/project/inc hello.c cc -o hello hello.o
And like this on Windows:
C:\>scons -Q hello.exe cl /Fohello.obj /c hello.c /nologo /Iinclude /I\home\project\inc link /nologo /OUT:hello.exe hello.obj