os.Args的第一个元素:os.Args[0],是命令本身的名字;其它的元素则是程序启动时传给它的参数
func main() { for index, item := range os.Args { fmt.Printf("index=%d,args=%s\n", index, item) } } go run os_args/main.go xxa a2 s3 d4 index=0,args=/tmp/go-build2136462296/b001/exe/main index=1,args=xxa index=2,args=a2 index=3,args=s3 index=4,args=d4
%d 十进制整数 %x, %o, %b 十六进制,八进制,二进制整数。 %f, %g, %e 浮点数: 3.141593 3.141592653589793 3.141593e+00 %t 布尔:true或false %c 字符(rune) (Unicode码点) %s 字符串 %q 带双引号的字符串"abc"或带单引号的字符'c' %v 变量的自然形式(natural format) %T 变量的类型 %p 十六进制表示,前缀 0x %% 字面上的百分号标志(无操作数)
当调用一个函数的时候,函数的每个调用参数将会被赋值给函数内部的参数变量,所以函数参数变量接收的是一个复制的副本,并不是原始调用的变量。因为函数参数传递的机制导致传递大的数组类型将是低效的,并且对数组参数的任何的修改都是发生在复制的数组上,并不能直接修改调用时原始的数组变量。
func main() { r := [...]int{99: -1} fmt.Printf("array r : %v\n", r) fmt.Printf("r:%p\n", &r) copyArray(r) fmt.Printf("array r : %v\n", r) } func copyArray(copyR [100]int) { fmt.Printf("copyR:%p\n", ©R) fmt.Printf("array copyR : %v\n", copyR) copyR[0] = 100 fmt.Printf("change array copyR : %v\n", copyR) } go run array/main.go array r : [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1] r:0xc00007c000 copyR:0xc00007c700 array copyR : [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1] change array copyR : [100 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1] array r : [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1]
slice值包含指向第一个slice元素的指针,因此向函数传递slice将允许在函数内部修改底层数组的元素(依然是拷贝,但是拷贝的对象持有原来的指针,对指针所指向值得修改将会影响到原值)
func main() { r := []int{99: -1} fmt.Printf("array r : %v\n", r) fmt.Printf("r:%p\n", &r) copyArray(r) fmt.Printf("array r : %v\n", r) } func copyArray(copyR []int) { fmt.Printf("copyR:%p\n", ©R) fmt.Printf("array copyR : %v\n", copyR) copyR[0] = 100 fmt.Printf("change array copyR : %v\n", copyR) } go run slice/main.go array r : [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1] r:0xc00000c030 copyR:0xc00000c060 array copyR : [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1] change array copyR : [100 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1] array r : [100 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1]
要在函数内部修改结构体成员的话,需要用指针传入,因为在Go语言中,所有的函数参数都是值拷贝传入的,函数参数将不再是函数调用时的原始变量
结构体的嵌入,访问属性麻烦
type Point struct { X, Y int } type Circle struct { Center Point Radius int } type Wheel struct { Circle Circle Spokes int } func main() { var w Wheel w.Circle.Center.X = 8 w.Circle.Center.Y = 8 w.Circle.Radius = 5 w.Spokes = 20 }
匿名成员
type Point struct { X, Y int } type Circle struct { Point Radius int } type Wheel struct { Circle Spokes int } func main() { var w Wheel //version 1 w.Circle.Point.X = 8 w.Circle.Point.Y = 8 w.Circle.Radius = 5 w.Spokes = 20 //version 2 w.Circle.X = 9 w.Circle.Y = 9 w.Circle.Radius = 10 w.Spokes = 10 //version 3 w.X = 1 w.Y = 2 w.Radius = 3 w.Spokes = 4 //结构体字面值必须遵循形状类型声明时的结构 w = Wheel{Circle{Point{1, 1}, 5}, 20} w = Wheel{ Circle: Circle{ Point: Point{X: 1, Y: 1}, Radius: 5, }, Spokes: 20, } }