Wrapping C Constants
$Header: /cvs/projects/SWIG/Examples/python/constants/index.html,v 1.1 2000/06/17 21:40:59 beazley Exp $
When SWIG encounters C preprocessor macros and C declarations that look like constants,
it creates Python variables with an identical value. Click here
to see a SWIG interface with some constant declarations in it.
Accessing Constants from Python
Click here to see a script that prints out the values
of the constants contained in the above file.
- The values of preprocessor macros are converted into Python constants.
- Types are inferred by syntax (e.g., "3" is an integer and "3.5" is a float).
- Character constants such as 'x' are converted into Python strings.
- C string literals such as "Hello World" are converted into Python strings.
- Macros that are not fully defined are simply ignored. For example:
is ignored because SWIG has no idea what type of variable this would be.
#define EXTERN extern
- Expressions are allowed provided that all of their components are defined. Otherwise, the constant is ignored.
- Certain C declarations involving 'const' are also turned into Python constants.
- The Python variables that SWIG creates are not protected from modification. For example,
even if you had this:
a user could come along in a script and type
#define FOO 73
Unfortunately, there's no easy way to prevent this.
example.FOO = 13
- The constants that appear in a SWIG interface file do not have to appear in any sort
of matching C source file since the creation of a constant does not require linkage
to a stored value (i.e., a value held in a C global variable or memory location).