[C++-sig] Re : Re : changing argument value in a C++/Python code, about initialisation

June 8, 2012

      I changed the first line of A::h to

C myC;
myC.setValue(0.);
this->g(&myC);

I don't know if it match your comment, but the result is myC read at 0 instead of a strange-value, which is still not 7.

CHRISTOPHE Jean-Joseph

________________________________
 De : Nat Linden <nat@lindenlab.com>
À : Development of Python/C++ integration <cplusplus-sig@python.org> 
Envoyé le : Vendredi 8 juin 2012 17h14
Objet : Re: [C++-sig] Re : changing argument value in a C++/Python code

On Fri, Jun 8, 2012 at 8:46 AM, christophe jean-joseph
<jjchristophe@yahoo.fr> wrote:
...
class C
{
public:
double myC;
C(){}
~C(){}
void setValue(double val) {
myC = val;
    }
    double getValue() {
return myC;
    }
};
...
class A
{
public:
...
C h(){ //This function wont be overloaded in Python
C myC;
this->g(&myC); //We want myC to be modified, and the python overloaded
version of g to be used
C calledC;
double myCint;
myCint = calledC.getValue();
cout << "Value back in C++: " << myCint << endl; //We want to verify if myC
has been modified back in C++
myCint = myCint*2;
calledC.setValue(myCint);
return myC;
}
};
When I run the code,  ...
cout << "Value back in C++: " <<
myCint << endl print -9.25596e+061 while I would like the variable to be at
7.
At risk of sounding foolish, your output looks reasonable to me.

In A::h(), at the point when you execute that cout << etc., this is
all the data that seems to participate:
...
C calledC;
double myCint;
myCint = calledC.getValue();
cout << "Value back in C++: " << myCint << endl;
You instantiate a brand-new 'C' object calledC. Its constructor
doesn't initialize C::myC, therefore it's uninitialized. You then call
calledC.getValue(), which returns that uninitialized double. myCint is
therefore a strange-looking value.
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