Make rng() const function: const gsl_rng* rng() const {.
wilx
2010-09-29 20:49:21
wilx is right. const gsl_rng* rng(){} only says that the returned pointer is const but you have to state that the function doesn't modify the object, too. This is the second const before the {}
fschmitt
2010-09-29 20:52:35
There's more to it than this.
John Dibling
2010-09-29 20:58:38
you guys are great!
Jerry Gagelman
2010-09-29 21:08:22
+3
A:
Change this function to:
const gsl_rng* rng() const {
return r_;
}
ybungalobill
2010-09-29 20:50:20
+2
A:
Two problems. First, you are calling a non-const member function through a const object reference. Can't do that. You can make GSLRand::rnd() a const member function:
const gsl_rng* rng() const {
...but then you have a second problem: gsl_rng() returns a const gsl_rng*, but you're trying to assign this to a non-const member variable. Can't do that, either.
Fork in the road. Either you always call const member functions on through the r_ pointer, or you sometimes call non-const member functions through it.
If you always call const member functions, then make the member variable point to a const gsl_rng:
const class gsl_rng* r_; // see links below
Otherwise, make your rng() function return a non-const pointer, while keeping the method itself const:
gsl_rng* rng() const {
return r_;
}
John Dibling
2010-09-29 20:57:48
Thanks for the detailed answer. I've always wondered what those <code>const</code> between the declaration and definition means. This is really helpful.
Jerry Gagelman
2010-09-29 21:07:08
@Jerry: You're welcome. Just by way of brief explanation, when you declare a member function `const`, you are telling the compiler to interpret the `this` pointer as `const`, so you won't be able to call any non-`const` member functions or change any non-`mutable` member variables.
John Dibling
2010-09-29 21:50:10