Use Function Adapters to Extend Generic Algorithms' Usage-2 : Page 2

Step 1: Demonstrating the Problem
Suppose you want to write an OS service that iterates through each of the currently active tasks. First, you store the Task objects in a container class such as std::vector:

class Task
{
public:
 explicit Task(int id) : pid(id) {}
 void show_pid() const 
 { 
  std::cout << "pid: " << pid << std::endl;
 }
//..
};

std::vector <Task> vt;
//populate the vector
vt.push_back(Task(1));
vt.push_back(Task(2));
vt.push_back(Task(3));

	Figure 1: Here's the output for this for-loop:.

The tricky part is traversing the vector. You can use a for-loop for this purpose (as shown in Figure 1):

for (std::vector<Task>::const_iterator it=vt.begin();
     it!=vt.end();
     ++it)
{ 
 it->show_pid(); //list every task's pid
}

However, this solution is only suitable for simple cases. In real world applications, for-loops such as this could become a maintenance problem. If you decide to use a different container, say std::list, you'll have to modify the for-loop as well:

for (std::list<Task>::const_iterator it=vt.begin();
//... 

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