11.4. Filtering Values Outside a Given Range
Problem
You want to ignore values from a sequence that fall above or below a given range.
Solution
Use the remove_copy_if function found in the
<algorithm>, as shown in Example 11-8.
Example 11-8. Removing elements from a sequence below a value
#include <algorithm>
#include <vector>
#include <iostream>
#include <iterator>
using namespace std;
struct OutOfRange
{
OutOfRange(int min, int max)
: min_(min), max_(max)
{ }
bool operator()(int x) {
return (x < min_) || (x > max_);
}
int min_;
int max_;
};
int main()
{
vector<int> v;
v.push_back(6);
v.push_back(12);
v.push_back(18);
v.push_back(24);
v.push_back(30);
remove_copy_if(v.begin(), v.end(),
ostream_iterator<int>(cout, "\n"), OutOfRange(10,25));
}The program in Example 11-8 produces the following output:
12 18 24
Discussion
The remove_copy_if
function copies the elements from one container to another container (or
output iterator), ignoring any elements that satisfy a predicate that you provide (it
probably would have been more accurate if the function was named copy_ignore_if). The function, however, does not change the size of the
target container. If, as is often the case, the number of elements copied by remove_copy_if is fewer than the size of the target container,
you will have to shrink the target container by calling the erase member function.
The function remove_copy_if requires a unary
predicate (a functor that takes one argument and returns a boolean value) that returns true when ...