NAME¶

std::uniform_real_distribution - std::uniform_real_distribution

Synopsis¶

Defined in header <random>
template< class RealType = double > (since C++11)
class uniform_real_distribution;

Produces random floating-point values \(\small x\)x, uniformly distributed on the
interval \(\small [a, b)\)[a, b), that is, distributed according to the probability
density function:

\({\small P(x|a,b) =} \frac{1}{b-a}\)P(x|a,b) =

1
b − a

.

std::uniform_real_distribution satisfies all requirements of
RandomNumberDistribution.

Template parameters¶

RealType - The result type generated by the generator. The effect is undefined if
this is not one of float, double, or long double.

Member types¶

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

Member functions¶

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

Generation¶

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

Characteristics¶

a returns the distribution parameters
b (public member function)
(C++11)
param gets or sets the distribution parameter object
(C++11) (public member function)
min returns the minimum potentially generated value
(C++11) (public member function)
max returns the maximum potentially generated value
(C++11) (public member function)

Non-member functions¶

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

Notes¶

It is difficult to create a distribution over the closed interval \(\small[a,
b]\)[a, b] from this distribution. Using std::nextafter(b,
std::numeric_limits<RealType>::max()) as the second parameter does not always work
due to rounding error.

Most existing implementations have a bug where they may occasionally return \(\small
b\)b (GCC #63176 LLVM #18767 MSVC STL #1074). This was originally only thought to
happen when RealType is float and when LWG issue 2524 is present, but it has since
been shown that neither is required to trigger the bug.

Example¶

Print 10 random numbers between 1 and 2.

// Run this code

#include <iostream>
#include <random>

int main()
{
std::random_device rd; // Will be used to obtain a seed for the random number engine
std::mt19937 gen(rd()); // Standard mersenne_twister_engine seeded with rd()
std::uniform_real_distribution<> dis(1.0, 2.0);
for (int n = 0; n < 10; ++n)
// Use dis to transform the random unsigned int generated by gen into a
// double in [1, 2). Each call to dis(gen) generates a new random double.
std::cout << dis(gen) << ' ';
std::cout << '\n';
}

Possible output:¶

1.80829 1.15391 1.18483 1.38969 1.36094 1.0648 1.97798 1.27984 1.68261 1.57326

External links¶

Drawing random floating-point numbers from an interval — © 2022. Frédéric Goualard,
Université de Nantes.