# std::generate_canonical

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< cpp‎ | numeric‎ | random

Defined in header `<random>` |  |
template< class RealType, size_t bits, class Generator > RealType generate_canonical( Generator& g ); |  | (since C++11)

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

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

- b = std::min<std::size_t>(bits, 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 [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. 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 (C++11) | produces real values evenly distributed across a range (class template)

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