一、一般操作
1,声明变量,go自动初始化为nil,长度:0,地址:0,nil
func main(){ var ss []string; fmt.Printf("length:%v \taddr:%p \tisnil:%v",len(ss),ss, ss==nil) }---Running...length:0 addr:0x0 isnil:trueSuccess: process exited with code 0.
2,切片的追加,删除,插入操作
func main(){
var ss []string;
fmt.Printf("[ local print ]\t:\t length:%v\taddr:%p\tisnil:%v\n",len(ss),ss, ss==nil)
print("func print",ss)
//切片尾部追加元素append elemnt
for i:=0;i<10;i++{
ss=append(ss,fmt.Sprintf("s%d",i));
}
fmt.Printf("[ local print ]\t:\tlength:%v\taddr:%p\tisnil:%v\n",len(ss),ss, ss==nil)
print("after append",ss)
//删除切片元素remove element at index
index:=5;
ss=append(ss[:index],ss[index+1:]...)
print("after delete",ss)
//在切片中间插入元素insert element at index;
//注意:保存后部剩余元素,必须新建一个临时切片
rear:=append([]string{},ss[index:]...)
ss=append(ss[0:index],"inserted")
ss=append(ss,rear...)
print("after insert",ss)
}
func print(msg string,ss []string){
fmt.Printf("[ %20s ]\t:\tlength:%v\taddr:%p\tisnil:%v\tcontent:%v",msg,len(ss),ss, ss==nil,ss)
fmt.Println()
}
------
Running...
[ local print ] : length:0 addr:0x0 isnil:true
[ func print ] : length:0 addr:0x0 isnil:true content:[]
[ local print ] : length:10 addr:0xc208056000 isnil:false
[ after append ] : length:10 addr:0xc208056000 isnil:false content:[s0 s1 s2 s3 s4 s5 s6 s7 s8 s9]
[ after delete ] : length:9 addr:0xc208056000 isnil:false content:[s0 s1 s2 s3 s4 s6 s7 s8 s9]
[ after insert ] : length:10 addr:0xc208056000 isnil:false content:[s0 s1 s2 s3 s4 inserted s6 s7 s8 s9]
Success: process exited with code 0.
3,copy的使用。
在使用copy复制切片之前,要保证目标切片有足够的大小,注意是大小,而不是容量,还是看例子:
func main() { var sa = make ([]string,0); for i:=0;i<10;i++{ sa=append(sa,fmt.Sprintf("%v",i)) } var da =make([]string,0,10); var cc=0; cc= copy(da,sa); fmt.Printf("copy to da(len=%d)\t%v\n",len(da),da) da = make([]string,5) cc=copy(da,sa); fmt.Printf("copy to da(len=%d)\tcopied=%d\t%v\n",len(da),cc,da) da = make([]string,10) cc =copy(da,sa); fmt.Printf("copy to da(len=%d)\tcopied=%d\t%v\n",len(da),cc,da) }---Running...copy to da(len=0) []copy to da(len=5) copied=5 [0 1 2 3 4]copy to da(len=10) copied=10 [0 1 2 3 4 5 6 7 8 9]
从上面运行结果,明显看出,目标切片大小0,容量10,copy不能复制。目标切片大小小于源切片大小,copy就按照目标切片大小复制,不会报错。
二、初始大小和容量
当我们使用make初始化切片的时候,必须给出size。go语言的书上一般都会告诉我们,当切片有足够大小的时候,append操作是非常快的。但是当给出初始大小后,我们得到的实际上是一个含有这个size数量切片类型的空元素,看例子:
func main(){ var ss=make([]string,10); ss=append(ss,"last"); print("after append",ss) }
---
Running...
[ after append ] : length:11 addr:0xc20804c000 isnil:false content:[ last]
实际上,此时我们应该先用下标为切片元素负值。但是如果我们既想有好的效率,有想继续使用append函数而不想区分是否有空的元素,此时就要请出make的第三个参数,容量,也就是我们通过传递给make,0的大小和足够大的容量数值就行了。
func main(){ var ss=make([]string,0,10); ss=append(ss,"last"); print("after append",ss) }---Running...[ after append ] : length:1 addr:0xc20804a000 isnil:false content:[last]
三、切片的指针。
1,当我们用append追加元素到切片时,如果容量不够,go就会创建一个新的切片变量,看下面程序的执行结果:
func main() { var sa []stringfmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa); for i:=0;i<10;i++{ sa=append(sa,fmt.Sprintf("%v",i)) fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa); } fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);}
---
Running ...
addr:0x0 len:0 content:[]addr:0x1030e0c8 len:1 content:[0]addr:0x10328120 len:2 content:[0 1]addr:0x10322180 len:3 content:[0 1 2]addr:0x10322180 len:4 content:[0 1 2 3]addr:0x10342080 len:5 content:[0 1 2 3 4]addr:0x10342080 len:6 content:[0 1 2 3 4 5]addr:0x10342080 len:7 content:[0 1 2 3 4 5 6]addr:0x10342080 len:8 content:[0 1 2 3 4 5 6 7]addr:0x10324a00 len:9 content:[0 1 2 3 4 5 6 7 8]addr:0x10324a00 len:10 content:[0 1 2 3 4 5 6 7 8 9]addr:0x10324a00 len:10 content:[0 1 2 3 4 5 6 7 8 9]
//很明显,切片的地址经过了数次改变。
2,如果,在make初始化切片的时候给出了足够的容量,append操作不会创建新的切片:
func main() { var sa = make ([]string,0,10);fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa); for i:=0;i<10;i++{ sa=append(sa,fmt.Sprintf("%v",i)) fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa); } fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);}
addr:0x10304140 len:0 content:[]addr:0x10304140 len:1 content:[0]addr:0x10304140 len:2 content:[0 1]addr:0x10304140 len:3 content:[0 1 2]addr:0x10304140 len:4 content:[0 1 2 3]addr:0x10304140 len:5 content:[0 1 2 3 4]addr:0x10304140 len:6 content:[0 1 2 3 4 5]addr:0x10304140 len:7 content:[0 1 2 3 4 5 6]addr:0x10304140 len:8 content:[0 1 2 3 4 5 6 7]addr:0x10304140 len:9 content:[0 1 2 3 4 5 6 7 8]addr:0x10304140 len:10 content:[0 1 2 3 4 5 6 7 8 9]addr:0x10304140 len:10 content:[0 1 2 3 4 5 6 7 8 9]
//可见,切片的地址一直保持不变
3, 如果不能准确预估切片的大小,又不想改变变量(如:为了共享数据的改变),这时候就要请出指针来帮忙了,下面程序中,sa就是osa这个切片的指针,我们共享切片数据和操作切片的时候都使用这个切片地址就ok了,其本质上是:append操作亦然会在需要的时候构造新的切片,不过是将地址都保存到了sa中,因此我们通过该指针始终可以访问到真正的数据。
func main() {
var osa = make ([]string,0);
sa:=&osa;
for i:=0;i<10;i++{
*sa=append(*sa,fmt.Sprintf("%v",i))
fmt.Printf("addr of osa:%p,\taddr:%p \t content:%v\n",osa,sa,sa);
}
fmt.Printf("addr of osa:%p,\taddr:%p \t content:%v\n",osa,sa,sa);
}
---
Running...
addr of osa:0xc20800a220, addr:0xc20801e020 content:&[0]
addr of osa:0xc20801e0a0, addr:0xc20801e020 content:&[0 1]
addr of osa:0xc20803e0c0, addr:0xc20801e020 content:&[0 1 2]
addr of osa:0xc20803e0c0, addr:0xc20801e020 content:&[0 1 2 3]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4 5]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4 5 6]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7]
addr of osa:0xc208052000, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7 8]
addr of osa:0xc208052000, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7 8 9]
addr of osa:0xc208052000, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7 8 9]
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