std::random_device::entropy

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< cpp‎ | numeric‎ | random‎ | random device
 
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random_device::entropy
 
double entropy() const;
 (since C++11)

Obtains an estimate of the random number device entropy, which is a floating-point value between min() and log
2(max()+1). If the device has n states whose individual probabilities are P
0,...,P
n-1, the device probability S is defined as

S = -Σn-1
i=0P
ilog(P
i)

A deterministic random number generator (e.g. a pseudo-random engine) has entropy zero.

Contents

[edit] Exceptions

noexcept specification:  
noexcept
  

[edit] Return value

The value of the device entropy, or zero if not applicable.

[edit] Notes

This function is not fully implemented in some standard libraries. For example, gcc and clang always return zero even though the device is non-deterministic. In comparison, Visual C++ always returns 32, and boost.random returns 10.

[edit] Example

Example output on one of the implementations

Run this code
#include <iostream>
#include <random>
 
int main()
{
    std::random_device rd;
    std::cout << rd.entropy() << '\n';
}

Possible output: 

32
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