Random number

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January 2024

There is no built-in entity to generate random numbers in Valve's Source Source games.

However, you can use logic_case's PickRandom input to trigger one of up to sixteen random outputs.


   // A generator of uniformly distributed random numbers
   class IUniformRandomStream
   	// Sets the seed of the random number generator
   	virtual void	SetSeed( int iSeed ) = 0;
   	// Generates random numbers
   	virtual float	RandomFloat( float flMinVal = 0.0f, float flMaxVal = 1.0f ) = 0;
   	virtual int		RandomInt( int iMinVal, int iMaxVal ) = 0;
   	virtual float	RandomFloatExp( float flMinVal = 0.0f, float flMaxVal = 1.0f, float flExponent = 1.0f ) = 0;

This is a random generator included in the source SDK, which allows you to generate random numbers, for instance to choose a random spawn point within an area:

   CEmpSpawn *picked = candidates[random->RandomInt(0, candidates.Count() - 1)];

random is a global set up in the initialization of the source SDK. Note the - 1; RandomInt(0,1) includes the upperbound, unlike its counterpart in the C++ stdlib and boost libraries. This upper bound behaviour can be readily tested by putting this anywhere you know will run:

   for (int i = 0; i < 50000; ++i) {
     Assert(random->RandomInt(0, 2) < 2);


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