Re: [Swig-user] get/set private C++ class member from Python - swig 1.3 vs. 2.0

[Christoph Schmidt-H. <chr...@gm...>]

On Thu, Oct 06, 2011 at 07:41:43AM +0100, William S Fulton wrote:
> On 26/09/11 12:18, Christoph Schmidt-Hieber wrote:
> >Hi,
> >
> >I'm trying to access a private member of a C++ class as an attribute of the corresponding Python class along the lines suggested here:
> >
> >http://www.swig.org/Doc1.3/SWIG.html#SWIG_adding_member_functions
> >
> >The goal is obviously to avoid non-Pythonic get/set functions while keeping the member private in C++. In brief, my C++ class looks like this:
> >
> >class Person {
> >public:
> >
> >     /* ... */
> >
> >     void set_age(double val) {age=val;}
> >     double get_age() const {return age;}
> >
> >private:
> >     double age;
> >
> >     /* ... */
> >
> >};
> >
> >In the swig interface file, I'm doing this, as suggested in the 1.3 documentation:
> >
> >class Person {
> >
> >     /* ... */
> >
> >     %extend {
> >         double age;
> >     }
> >
> >     /* ... */
> >
> >};
> >
> >%{
> >     double Person_age_get(Person *p) {
> >         return p->get_age();
> >     }
> >     void Person_age_set(Person *p, double val) {
> >         p->set_age(val);
> >     }
> >}
> >
> >While this code works fine in swig 2.0.4, it results in an error message with swig 1.3 because the set_ function is supposed to return a pointer of some sort; e.g.:
> >
> >error: could not convert ‘Person_age_set(arg1, arg2)’ to ‘bool’
> >error: type ‘void’ argument given to ‘delete’, expected pointer
> >
> >How can I get this to run with both 1.3 and 2.0?
> 
> I can't replicate this with 1.3.29 or later, I'm not sure which
> version you are using. But in any case, you can deal with different
> SWIG versions using the preprocessor and the SWIG_VERSION, eg:
> 
> #if SWIG_VERSION<0x020000
> // swig 1.3.x
> #else
> // swig 2.0.0 and later
> #endif
> 
> William

Thanks for your reply. I apologise for the incomplete example - turns out that this problem only appears with char*, but not with double. I'm now resorting to using std::string throughout, which seems to work with both 1.3 and 2.0.

Cheers,
Christoph