Question

I am doing some experiments on the slice, When i assign value to a slice with in the length range, it worked fine But when i assign value to a slice with in the cap range without append() func, it gave me runtime error.

Eg: mySlice := make([]int, 3, 5) mySlice[3] = 4 // runtime error

If capacity in make function means, the total space already been allocated for the slice. Then, why i am not able to access that location with indexing?? Why only we can store values using append() func only, if we want to assign value more than length range specified but in the cap range??

package main

import "fmt"

func main() {
    mySlice := make([]int, 3, 5)
    mySlice[0] = 1
    mySlice[1] = 2
    mySlice[2] = 3
    mySlice[3] = 4  `This giving me error saying that "index out of range [3] with length 3"`    
    fmt.Println("mySlice....", mySlice)
}

Answer 1

切片的长度是它所含元素的数量。

切片的容量是底部数组中元素的数量,从切片的第一个元素中计算。

您在下面的调用中定义了 len = 3, cap = 5 的切片。

make([]int, 3, 5)

所以,这就是为什么 < code> myClice[3] = 4 = 4 超出范围。您可以打印切片的长度和容量来检查这一点。

fmt.Printf("len=%d cap=%d", len(mySlice), cap(mySlice))
//len=3 cap=5

另一方面,附加函数将增长切片, 您可以检查此 < a href=" https:// go. dev/ blog/ slices- intro" rel= " no follown noreferrer" >slips intro documents 。因此, 您可以毫无错误地使用 < code> 附录。

mySlice = append(mySlice, 4)
//len=4 cap=5

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