golang 切片傳參

golang切片傳參，一般認為傳參為引用傳參，如果修改函數內的slice值，則main函數中的切片數值發生改變， 但是只用append函數給slice添加數據后，main函數里面的slice數組並沒有變化。

實際是因為slice作為參數傳遞時值傳遞，傳遞的是slice的底層結構體，復制了一個數組指針，len和cap。

雖然ap函數里面的數組指針里面的數組里面的數據有所增加，或者更換了底層數組指針，但是main函數中的仍然為原來的slice結構體，所以沒有改變。

package main
 
 
import (
        "fmt"
        "unsafe"
)
 
 
func main() {
        slice := []int{}
        fmt.Printf("main slice:%v &slice:%p unsafe.Pointer:%p  slice:%p len:%d cap:%v\n", slice, &slice,  unsafe.Pointer(&slice), slice, len(slice), cap(slice))
        slice = append(slice, 1, 2, 3, 4, 5)
        fmt.Printf("main slice:%v &slice:%p unsafe.Pointer:%p  slice:%p len:%d cap:%v\n", slice, &slice,  unsafe.Pointer(&slice), slice, len(slice), cap(slice))
        slice = append(slice, 6)
        fmt.Printf("main slice:%v &slice:%p unsafe.Pointer:%p  slice:%p len:%d cap:%v\n", slice, &slice,  unsafe.Pointer(&slice), slice, len(slice), cap(slice))
        slice = append(slice, 7)
        fmt.Printf("main slice:%v &slice:%p unsafe.Pointer:%p  slice:%p len:%d cap:%v\n", slice, &slice,  unsafe.Pointer(&slice), slice, len(slice), cap(slice))
        ap(slice)
        fmt.Printf("main slice:%v &slice:%p unsafe.Pointer:%p  slice:%p len:%d cap:%v\n", slice, &slice,  unsafe.Pointer(&slice), slice, len(slice), cap(slice))
}
 
 
func ap(slice []int) {
        fmt.Printf("ap slice:%v &slice:%p unsafe.Pointer:%p  slice:%p len:%d cap:%v\n", slice, &slice,  unsafe.Pointer(&slice), slice, len(slice), cap(slice))
        slice[0] = 10
        slice = append(slice, 10)
        fmt.Printf("ap slice:%v &slice:%p unsafe.Pointer:%p  slice:%p len:%d cap:%v\n", slice, &slice,  unsafe.Pointer(&slice), slice, len(slice), cap(slice))
}

 

 

注：切片的取地址的%p取的地址為底層數組的指針地址