11.8. Representing a Dynamically Sized Numerical Vector
Problem
You want a type for manipulating numerical vectors with dynamic size.
Solution
You can use the valarray
template from the <valarray>
header.
Example 11-15 shows how you can use
the valarray
template.
Example 11-15. Using valarray
#include <valarray> #include <iostream> using namespace std; int main() { valarray<int> v(3); v[0] = 1; v[1] = 2; v[2] = 3; cout << v[0] << ", " << v[1] << ", " << v[2] << endl; v = v + v; cout << v[0] << ", " << v[1] << ", " << v[2] << endl; v /= 2; cout << v[0] << ", " << v[1] << ", " << v[2] << endl; }
The program in Example 11-15 will output the following:
1, 2, 3 2, 4, 6 1, 2, 3
Discussion
Despite its name, vector
is not intended to be used
as a numerical vector; rather, the valarray
template
is. The valarray
is designed so that C++
implementations, especially those on high-performance machines, can apply specialized
vector optimizations to it. The other big advantage of valarray
is that it provides numerous overloaded operators specifically for
working with numerical vectors. These operators provide such functionality as vector
addition and scalar multiplication.
The valarray
template can also be used with the
standard algorithms like a C-style array. See Example 11-16 to see how you can create iterators to the beginning of, and one past the end of, a
valarray
.
Example 11-16. Getting iterators to valarray
template<class T> T* valarray_begin(valarray<T>& x) { return &x[0]; } template<class T> T* ...
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