# std::uniform_real_distribution

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< cpp‎ | numeric‎ | random

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

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) (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

ab (C++11) | returns the distribution parameters (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)

### 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.

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