Re: is it ok to cast variables? simple function using std::pow
On Jun 7, 3:58 am, aaragon <alejandro.ara...@gmail.com> wrote:
I wrote a very simple function to try to understand the casting of
variables in C++. The function is
function foo()
{
std::vector<int> test(100);
randomize(test);
unsigned long x = 0;
for(int i=0; i<test.size(); i++)
x += (unsigned long)(allele(i)*std::pow((double)k,
(double)i));
}
The function randomize just creates random values inside the vector.
This was the only way I made it to work without having any warnings
from the compiler. Since the std::pow takes two doubles as parameters,
I needed to cast the integer values into doubles.
Nonsense. Int's convert implicitly to double, and it's a
non-lossy conversion, so there's not even the slightest excuse
for a warning.
Also, I needed to
cast those double results into an unsigned long integer.
That's also an implicit conversion, although since it is a lossy
one, a warning is somewhat understandable. I would use a cast
here, if only to tell the reader that I meant it.
I don't
really like using casting (I have a bad feeling every time I use it)
but I couldn't find a better way to do this. Does anyone have a better
way to do it? Is there anything wrong with casting variables into
different types?
Well, there's certainly nothing wrong with converting a value to
a different type, when that's what you want. Sometimes, it's
even necessary:
std::cout << instanceCount / totalCount * 100 << " percent" ;
won't give the desired results unless you convert at least one
of instanceCount or totalCount to a floating point type. And
surely you've written things like:
f( std::string( a ) + ".txt" ) ;
, casting a C style string to an std::string.
These are conversion casts, involving values, and there's
generally nothing wrong with them. If the conversion is "lossy"
(the target type can't hold all of the information present in
the orginal type), then some care should be exercised,
particularly in cases like converting to an integral value from a
floating point (where there are several different rounding rules
you might want to apply), but otherwise, I see no problem with
them.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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