NAME¶

std::generate_canonical - std::generate_canonical

Synopsis¶

Defined in header <random>
template< class RealType, std::size_t Bits, class Generator > (since C++11)
RealType generate_canonical( Generator& g );

Generates a random floating point number in range \(\small [0,1)\)[0, 1).

To generate enough entropy, generate_canonical() will call g() exactly \(\small k\)k
times, where \(\small k = \max(1, \lceil \frac{b}{\log_2 R} \rceil)\)k = max(1, ⌈
b / log
2 R ⌉) and

* b = std::min(Bits, std::size_t{std::numeric_limits<RealType>::digits}),
* R = g.max() - g.min() + 1.

Parameters¶

g - generator to use to acquire entropy

Return value¶

Floating point value in range \(\small [0,1)\)[0, 1).

Exceptions¶

None except from those thrown by g

Notes¶

Some existing implementations have a bug where they may occasionally return 1.0 if
RealType is float GCC #63176 LLVM #18767 MSVC STL #1074. This is LWG issue 2524.

Example¶

produce random numbers with 10 bits of randomness: this may produce only k*R
distinct values

// Run this code

#include <random>
#include <iostream>

int main()
{
std::random_device rd;
std::mt19937 gen(rd());
for(int n=0; n<10; ++n) {
std::cout << std::generate_canonical<double, 10>(gen) << ' ';
}
}

Possible output:¶

0.208143 0.824147 0.0278604 0.343183 0.0173263 0.864057 0.647037 0.539467 0.0583497 0.609219

See also¶

uniform_real_distribution produces real values evenly distributed across a range
(C++11) (class template)