Why does the Go slicing capacity become 6 after adding elements?

Why does the Go slicing capacity become 6 after adding elements?

When the append function of Go language adds elements to the slice, its capacity sometimes changes, which is related to the memory management strategy of Go language. Let's analyze it with an example:

 package main

import "fmt"

func main() {
    var s []int
    printSlice(s) // len=0 cap=0 []

    s = append(s, 0)
    printSlice(s) // len=1 cap=1 [0]

    s = append(s, 1)
    printSlice(s) // len=2 cap=2 [0 1]

    s = append(s, 2, 3, 4)
    printSlice(s) // len=5 cap=6 [0 1 2 3 4] Why is the capacity 6?
}

func printSlice(s []int) {
    fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}

After the last append operation, the slice capacity becomes 6 instead of 5. This is because the runtime of Go will dynamically adjust the capacity of slices as needed to reduce the overhead of memory allocation and data replication. Go does not reallocate memory every time an element is added, but pre-allocates larger space to deal with subsequent element additions. This strategy improves program efficiency.

The calculation of specific capacity is not a fixed algorithm. It is related to the memory allocation strategy during Go runtime and the current system environment, and may also differ slightly due to the Go language version. The key is that the slicing design of Go is designed to balance performance and memory management flexibility. While we cannot predict capacity accurately, we can understand the optimization mechanism behind it: preallocate space to avoid frequent memory allocation and data replication.

The above is the detailed content of Why does the Go slicing capacity become 6 after adding elements?. For more information, please follow other related articles on the PHP Chinese website!