 2017-08-18 09:38

# 为什么要重复相同的随机数？

I'm new to Go and not sure why it prints the same number for `rand.Intn(n int) int` for every run:

``````package main

import (
"fmt"
"math/rand"
)

func main() {
fmt.Println(rand.Intn(10))
}
``````

The docs says :

Intn returns, as an int, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.

And how do I properly seed the random number generation?

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#### 3条回答默认 最新

• dth20986 2017-08-18 09:42
已采纳

By calling the `rand.Seed()` function, passing it a (random) seed (typically the current unix timestamp). Quoting from `math/rand` package doc:

Top-level functions, such as Float64 and Int, use a default shared Source that produces a deterministic sequence of values each time a program is run. Use the Seed function to initialize the default Source if different behavior is required for each run.

Example:

``````rand.Seed(time.Now().UnixNano())
``````

If `rand.Seed()` is not called, the generator behaves as if seeded by 1:

Seed uses the provided seed value to initialize the default Source to a deterministic state. If Seed is not called, the generator behaves as if seeded by Seed(1).

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• dongyata3336 2017-12-28 22:26
``````package main

import

(
"fmt"
"math/rand"
"time"
)

func randomGen(min, max int) int {
rand.Seed(time.Now().Unix())
return rand.Intn(max - min) + min
}

func main() {
randNum := randomGen(1, 10)
fmt.Println(randNum)
}
``````
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• doude4924 2018-08-22 12:39

Under the package, math/rand, you can find a type Rand.

func New(src Source) *Rand - New returns a new Rand that uses random values from src to generate other random values.

It actually needs a seed to generate it.

1. step 1: create a seed as a source using new Source. time.Now().UnixNano() is used for the accuracy.
2. step 2: create a type Rand from the seed
3. step 3: generate a random number.

Example:

``````package main

import (
"fmt"
"math/rand"
"time"
)

func main() {
source := rand.NewSource(time.Now().UnixNano())
r := rand.New(source)
fmt.Println(r.Intn(100))
}
``````
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