Version 5.0 The LEDA User Manual

2. Creation
CompPred cp(const DA& da, const Comp& comp,
typename DA:: value type val);
introduces a variable cp of this class and associates it to the given
data accessor da, compare function comp and value val.
Precondition: Comp is a pointer-to-function type which takes two values
of type typename DA:: value type and produces a boolean return
value. Comp might also be a class with member function
bool operator( )(typename DA:: value type, typename DA:: value type).
3. Example
In the following example, a node iterator for red nodes will be created. At first the basic
part (see sect. 13.13 for explanation of the data accessor node array da):
graph G;
NodeIt it(G);
node_array na_colour(G,black);
node_array_da da_colour(na_colour);
assign_some_color_to_each_node();
Now follows the definition of a “red iterator” (Equal yields true, if the given two values
are equal):
template
class Equal {
public:
bool operator() (T t1, T t2) const {
return t1==t2; }
};
typedef CompPred Predicate;
Predicate PredColour(da_colour,Equal(),red);
FilterNodeIt red_it(PredColour,it);
This simplifies the loop to the following:
while(red_it.valid()) {
do_something(red_it);
++red_it; }