# std::bernoulli_distribution

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< cpp‎ | numeric‎ | random

Defined in header `<random>` |  |
class bernoulli_distribution; |  | (since C++11)

Produces random boolean values, according to the discrete probability function. The probability of true is

  P(b|p) =⎧
  ⎨
  ⎩p, if b is true
  1 − p, if b is false

`std::bernoulli_distribution` satisfies RandomNumberDistribution.

### Member types

Member type | Definition
`result_type` (C++11) | bool
`param_type` (C++11) | the type of the parameter set, see RandomNumberDistribution.

### Member functions

(constructor) (C++11) | constructs new distribution (public member function)
reset (C++11) | resets the internal state of the distribution (public member function)

##### Generation

operator() (C++11) | generates the next random number in the distribution (public member function)

##### Characteristics

p (C++11) | returns the p distribution parameter (probability of generating true) (public member function)
param (C++11) | gets or sets the distribution parameter object (public member function)
min (C++11) | returns the minimum potentially generated value (public member function)
max (C++11) | returns the maximum potentially generated value (public member function)

### Non-member functions

operator==operator!= (C++11)(C++11)(removed in C++20) | compares two distribution objects (function)
operator<<operator>> (C++11) | performs stream input and output on pseudo-random number distribution (function template)

### Example

Run this code

    #include <iomanip>
    #include <iostream>
    #include <map>
    #include <random>
    #include <string>

    int main()
    {
        std::random_device rd;
        std::mt19937 gen(rd());
        // give "true" 1/4 of the time
        // give "false" 3/4 of the time
        std::bernoulli_distribution d(0.25);

        std::map<bool, int> hist;
        for (int n = 0; n < 10000; ++n)
            ++hist[d(gen)];

        std::cout << std::boolalpha;
        for (auto const& [key, value] : hist)
            std::cout << std::setw(5) << key << ' '
                      << std::string(value / 500, '*') << '\n';
    }

Possible output:

    false ***************
     true ****

### External links

Weisstein, Eric W. "Bernoulli Distribution." From MathWorld — A Wolfram Web Resource.

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