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Tip of the Day
Language: C++
Expertise: Beginner
Jan 4, 2005

The generate() Algorithm

You can use the generate() algorithm to fill up a sequence container with values that you generate by repeatedly calling a function. This algorithm takes three arguments. The first two arguments are forward iterators marking the range and the third one is the function pointer—or function object that returns values to be filled in the sequencer container.

Suppose you want fill a vector with numbers sequentially, but want to fill 0 for those number which are not divisible by 3:


	class gen
	{
		public:
		int operator () ()
		{
			static int i = 0;

			++i;

			return i%3 ? 0 : i;
		}
	};

	#include <algorithm> //for generate()
	#include <vector> //for vector


	vector<int> vecInt(10);


	generate(vecInt.begin(), vecInt.end(), gen() ); // 0 0 3 0 0 6 0 0 9 0
The generate_n() algorithm is similar in that it invokes the function (the third argument) as many times as is specified in its second argument to fill up the sequence container.

	#include <list> //for list

	list<tint> lstInt;

	generate_n(back_inserter(lstInt), 5, gen());
The above statement invokes gen().
Saurabh Ramya
 
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