Re: how to best use valarrays as constructor arguments
In message <e8tqag$lal$1@localhost.localdomain>, Gerard Kramer
<replytogroup@usenet.com> writes
Victor Bazarov wrote:
Gerard Kramer wrote:
Presently I have some difficulties with the following type of code
which is understandably causing a segfault:
//---- begin code ----
#include <valarray>
#include <iostream>
using namespace std;
class SomeClass {
private:
valarray <double> mx;
public:
SomeClass(valarray <double>& x)
I'd recommend making this take a const reference, but it shouldn't make
any difference to the rest of the code.
.... and I'd recommend using an initializer list, but again it shouldn't
make any difference.
: mx(x) {}
void func() {cout << mx[1];} // <---- Segfault here.
.... and this really ought to be a const member function, but again it
shouldn't matter.
Really?!!
yes ;-)
};
int main () {
valarray <double> x(5,10);
SomeClass foo(x);
foo.func();
return 0;
}
//---- end code ----
It will fail at runtime because, as I understand it, mx is a zero-size
valarray and hence mx[1] does not exist.
It *will* fail or it *does* fail?
It *will* fail (by looking at the code)
Can you describe, line by line, what you think the code is doing?
and so it *does* (by compiling
and running it.)
With the exception of using assignment instead of initialisation and some
superfluousness and extraneous whitespace, your code is fine, AFAICT.
Yet (for a simple numerical code) I would like something similar to
the above to work, i.e. I'd like to pass a valarray of predefined
size to the constructor of a class to initialize a class-member
valarray, say mx, and after reference to mx's elements as mx[0],
mx[1] etc. As a C++ starter I'm confused about the best way to work
around the problem in the code above. Any advice would be welcome.
What problem? Prove to us there is a problem, post the results of your
run, not your speculations. Step through it in a debugger. Print out
the *size* of 'mx' instead of its element. Anyway, do something, don't
just stand there.
I'm sorry? Well, thanks for the reply. As far as I can see I didn't
speculate about anything. Just to be clear: There is no problem, but I'd
like to learn how to get a certain thing done, namely:
The best way to somehow to use a valarray <double> as an argument of a
class constructor to initialize a class member variable of type valarray
<double>.
SomeClass(valarray <double> const & x) : mx(x) {}
I can't see how to do that.
That's all. I'm sorry in case that bothered you. Won't happen again.
V
--
Richard Herring