Programming Forums > Application Development > C++

Ben.Dougall · Jul 5th, 2007, 7:03 PM

Hi guys, new to the forum, plan to contribute here a lot as i get bored at work. Quick question on a Random Generator.

I'm making a library for common tasks in C++ ( random, XML Reader, HTML Document maker, etc ) and I am just wondering the best way to go about this is. Right now, even though it is templated, doubles and floats are never real numbers, always whole numbers.

 cpp Syntax (Toggle Plain Text) 
	/**
	@brief	Seeds the Random Number generator 
	@param	seed	The value to seed the generator with.
	@note	The generator is only seeded once, no matter how many times you call the method */
	void SeedGenerator( int seed = static_cast<int>( time(0) ) ) 
	{
		static bool seeded = false;
		if ( !seeded )
		{
			srand( seed );
			rand();
			seeded = true;
		}
	}
 
	/**
	@brief	Generates Random Number
	@param	low		The lowest possible number
	@param	high	The highest possible number
	@return	The random number between the range.
	*/
	template <typename T>
	inline T RandomNumber( const T &low, const T &high )
	{
		return static_cast<T>(low + rand() % high ); 
	}
	/**
	@brief	Seeds the Random Number generator 
	@param	seed	The value to seed the generator with.
	@note	The generator is only seeded once, no matter how many times you call the method */
	void SeedGenerator( int seed = static_cast<int>( time(0) ) ) 
	{
		static bool seeded = false;
		if ( !seeded )
		{
			srand( seed );
			rand();
			seeded = true;
		}
	}

	/**
	@brief	Generates Random Number
	@param	low		The lowest possible number
	@param	high	The highest possible number
	@return	The random number between the range.
	*/
	template <typename T>
	inline T RandomNumber( const T &low, const T &high )
	{
		return static_cast<T>(low + rand() % high ); 
	}

I have been using this formula for 4 years during Java development, and works fine for whole number generation. I was just wondering what the best, and most efficent method of doing this would be.

lectricpharaoh · Jul 6th, 2007, 1:41 AM

Quote:

Originally Posted by Ben.Dougall

Hi guys, new to the forum, plan to contribute here a lot as i get bored at work. Quick question on a Random Generator.

That's as good a reason as any, I suppose. Let me be the first to welcome you to the forums.

Quote:

Originally Posted by Ben.Dougall

I have been using this formula for 4 years during Java development, and works fine for whole number generation. I was just wondering what the best, and most efficent method of doing this would be.

Narue has an excellent article here on using rand(), particularly how to use it effectively, avoiding common pitfalls that often yield sequences that are 'less random'. She also has another article that shows you how to roll your own psuedo-random number generator. This might be necessary if the implementation in your compiler's libraries is poor, or simply because you want to have multiple concurrent generators active. As an example of why you might need multiple generators, imagine a Tetris clone that allowed two-player head-to-head games. By using different generators seeded with the same value, you guarantee neither player gets an advantage by having better pieces (since they both get the same pieces in the same order).

Ben.Dougall · Jul 6th, 2007, 10:13 AM

Thanks for the info, those articles are quite useful. I'll give it a try when I get some time.

Thanks again.

Ben.Dougall · Jul 6th, 2007, 7:09 PM

 cpp Syntax (Toggle Plain Text) 
static_cast<T>(low + rand() / ( RAND_MAX / ( high - low ) + 1 ));
static_cast<T>(low + rand() / ( RAND_MAX / ( high - low ) + 1 ));

Thank you Lectric, the first link you gave me seems to have done the job.

DaWei · Jul 6th, 2007, 7:19 PM

You understand that the return of rand, as usually implemeted in C/C++, is an integer, right? Casting doesn't give you a real number.

Ben.Dougall · Jul 6th, 2007, 7:42 PM

Quote:

Originally Posted by DaWei

You understand that the return of rand, as usually implemeted in C/C++, is an integer, right? Casting doesn't give you a real number.

True, I had that in to eliminate a warning I got with a former formula. One of my professors docked 30% if a compile warning occured. Removed, and no warning. Thanks for your eyes on that one.

I have a feeling i can learn a lot from this forum. Thank again Dawei and lectric.

Jul 5th, 2007, 7:03 PM	#1
Ben.Dougall Programmer Join Date: Jul 2007 Location: London, Ontario, Canada Posts: 34 Rep Power: 0	Templated Random Number Generator Hi guys, new to the forum, plan to contribute here a lot as i get bored at work. Quick question on a Random Generator. I'm making a library for common tasks in C++ ( random, XML Reader, HTML Document maker, etc ) and I am just wondering the best way to go about this is. Right now, even though it is templated, doubles and floats are never real numbers, always whole numbers. cpp Syntax (Toggle Plain Text) /** @brief Seeds the Random Number generator @param seed The value to seed the generator with. @note The generator is only seeded once, no matter how many times you call the method / void SeedGenerator( int seed = static_cast<int>( time(0) ) ) { static bool seeded = false; if ( !seeded ) { srand( seed ); rand(); seeded = true; } } /* @brief Generates Random Number @param low The lowest possible number @param high The highest possible number @return The random number between the range. / template <typename T> inline T RandomNumber( const T &low, const T &high ) { return static_cast<T>(low + rand() % high ); } /* @brief Seeds the Random Number generator @param seed The value to seed the generator with. @note The generator is only seeded once, no matter how many times you call the method / void SeedGenerator( int seed = static_cast<int>( time(0) ) ) { static bool seeded = false; if ( !seeded ) { srand( seed ); rand(); seeded = true; } } /* @brief Generates Random Number @param low The lowest possible number @param high The highest possible number @return The random number between the range. / template <typename T> inline T RandomNumber( const T &low, const T &high ) { return static_cast<T>(low + rand() % high ); } I have been using this formula for 4 years during Java development, and works fine for whole number generation. I was just wondering what the best, and most efficent method of doing this would be. Last edited by Ben.Dougall; Jul 5th, 2007 at 7:39 PM.*

Jul 6th, 2007, 7:09 PM	#4
Ben.Dougall Programmer Join Date: Jul 2007 Location: London, Ontario, Canada Posts: 34 Rep Power: 0	cpp Syntax (Toggle Plain Text) static_cast<T>(low + rand() / ( RAND_MAX / ( high - low ) + 1 )); static_cast<T>(low + rand() / ( RAND_MAX / ( high - low ) + 1 )); Thank you Lectric, the first link you gave me seems to have done the job.

Jul 6th, 2007, 7:19 PM	#5
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	You understand that the return of rand, as usually implemeted in C/C++, is an integer, right? Casting doesn't give you a real number. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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Jul 6th, 2007, 10:13 AM	#3
Ben.Dougall Programmer Join Date: Jul 2007 Location: London, Ontario, Canada Posts: 34 Rep Power: 0	Thanks for the info, those articles are quite useful. I'll give it a try when I get some time. Thanks again.

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Programming Forums > Application Development > C++

Templated Random Number Generator