Generate random numbers, characters and slice elements

Go pseudo-random number basics

Use the rand.Seed and rand.Int63 functions in package math/rand to generate a non-negative pseudo-random number of type int64:

rand.Seed(time.Now().UnixNano())
n := rand.Int63() // for example 4601851300195147788

Similarly, rand.Float64 generates a pseudo-random float x, where 0 ≤ x < 1:

x := rand.Float64() // for example 0.49893371771268225

Warning: Without an initial call to rand.Seed, you will get the same sequence of numbers each time you run the program.

See What’s a seed in a random number generator? for an explanation of pseuodo-random number generators.

Several random sources

The functions in the math/rand package all use a single random source.

If needed, you can create a new random generator of type Rand with its own source, and then use its methods to generate random numbers:

generator := rand.New(rand.NewSource(time.Now().UnixNano()))
n := generator.Int63()
x := generator.Float64()

Integers and characters in a given range

Number between a and b

Use rand.Intn(m), which returns a pseudo-random number n, where 0 ≤ n < m.

n := a + rand.Intn(b-a+1) // a ≤ n ≤ b

Character between 'a' and 'z'

c := 'a' + rune(rand.Intn('z'-'a'+1)) // 'a' ≤ c ≤ 'z'

Random element from slice

To generate a character from an arbitrary set, choose a random index from a slice of characters:

chars := []rune("AB⌘")
c := chars[rand.Intn(len(chars))] // for example '⌘'

Further reading

Runes and character encoding

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