Go-Maps
2016-08-31 14:17
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语法汇总
前面介绍的array、slice都是顺序性列表,本节的map则是无序的。这个map和C/C++/Java的map一样,在Python中称为字典/dictionary。但Golang中map的用法更符合脚本语言的特点,和Python很像。
涉及的主要语法点:
var the_map map[string]int the_map := make(map[string]int) the_map := map[string]int {key:value, ...} value, ok := the_map[key]
示例-基本用法
下面这个例子给出了map的声明方法。但通常并不这么使用,因为这种声明之后必须要调用make()初始化之后才可赋值,与其这样,不如直接:= make()这种方式。package main /* D:\examples>go run helloworld.go panic: assignment to entry in nil map goroutine 1 [running]: panic(0x45a540, 0xc04203a000) C:/Go/src/runtime/panic.go:500 +0x1af main.main() D:/examples/helloworld.go:13 +0x6f exit status 2 D:\examples> */ func main() { //x is a map of strings to ints. -- Reference: <<Introducing Go>> Slice, Map, P38 var x map[string]int x["first"] = 1 }
示例-make()
package main import "fmt" /* D:\examples>go run helloworld.go x: 1 2 D:\examples> */ func main() { x := make(map[string]int) x["first"] = 1 x["second"] = 2 debug_map(x, "x:") } func debug_map(the_map map[string]int, msg string) { fmt.Print(msg, "\t") for _, item := range the_map { fmt.Print(item, "\t") } fmt.Println() }
示例-make与初始化列表
这里所谓“初始化列表”借用C++的initialization list。在make的同时,给map指定key:value列表。package main import "fmt" /* D:\examples>go run helloworld.go x: 1 2 D:\examples> */ func main() { x := map[string]int { "first" : 1, "second" : 2, } debug_map(x, "x:") } func debug_map(the_map map[string]int, msg string) { fmt.Print(msg, "\t") for _, item := range the_map { fmt.Print(item, "\t") } fmt.Println() }
示例-判断元素是否存在
即便key不存在,调用the_map[the_key]的时候也不会抛出运行时异常。这和编译型语言、以及脚本语言Python都不一样。Go的处理方式更为优雅,写的代码行数也少。package main import "fmt" /* D:\examples>go run helloworld.go a: 1 b: 0 value: 1 , exist: true Exist value: 0 , exist: false Not exist. D:\examples> */ func main() { x := map[string]int { "first" : 1, "second" : 2, } a := x["first"] b := x["third"] fmt.Println("a: ", a) fmt.Println("b: ", b) find_map(x, "first") find_map(x, "fourth") } func debug_map(the_map map[string]int, msg string) { fmt.Print(msg, "\t") for _, item := range the_map { fmt.Print(item, "\t") } fmt.Println() } func find_map(the_map map[string]int, key string) { value, exist := the_map[key] fmt.Println("value: ", value, ", exist: ", exist) if exist { fmt.Println("Exist") } else { fmt.Println("Not exist.") } }
value
map的value可以是任何的数据,比如value本身也可以是map。这是Introducing Go中给出的例子,这里不再展开。删除元素&判断是否存在
package main import "fmt" func main() { values := make(map[int]string) values[1] = "One" values[2] = "two" values[3] = "three" //values: map[1:One 2:two 3:three] fmt.Println("values:", values) delete(values, 2) //values: map[1:One 3:three] fmt.Println("values:", values) value, found := values[2] //value: , found: false fmt.Println("value:", value, ", found:", found) }
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