Go 学习笔记：数据类型

数据类型

Golang 支持多种数据类型，包括布尔型，int， float（float32， float64），字符串类型，还有一系列的派生类型

Golang 没有long long和double类型，取而代之的是（int64 和 float64）

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:15:49
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

func main() {
    var intNum int
    var float32Num float32
    var float64Num float64
    var boolNum bool
    var str string

    fmt.Println(
        intNum,
        float32Num,
        float64Num,
        boolNum,
        str) // 声明后不使用会编译错误
}

变量声明

Golang有多种声明变量的方法，比如：

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:15:49
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

func main() {
    var s string = "Hello world"
    fmt.Println(s)
}

当然，你也可以一次性申请多个变量：

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:21:55
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

func main() {
    var s1, s2, s3, s4 string = "Hello", "world", "my", "dear"
    fmt.Println(s1, s2, s3, s4)
}

在书写上述代码的时候，你也可以通过Go根据值自动判断变量类型的特性，来简写上述代码

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:25:29
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

func main() {
    var s1, s2, s3, s4 = "Hello", "world", "my", "dears"
    fmt.Println(s1, s2, s3, s4)
}

除了通过var来声明变量，我们还可以使用:=来声明变量，则上面的代码会变为

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:25:29
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

func main() {
    s1, s2, s3, s4 := "Hello", "world", "my", "dears" 
    // 如果左侧出现了已有的变量，则会报错
    fmt.Println(s1, s2, s3, s4)
}

值得注意的是，这种声明方法只能在函数体内使用

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:25:29
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

glb := 12 // 这样书写是错误的

func main() {
    fmt.Println(gbl)
}

一般我们再书写全局变量的时候，是这样写的

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:40:59
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

var (
    RED   string = "red"
    GREEN string = "green"
    BLUE  string = "blue"
)

func main() {
    fmt.Println(RED, GREEN, BLUE)
}

补充：在交换代码值的时候，可以参考Python的一些写法，而毋需再声明新的变量

/*
 * @Author: NorthCityChen
 * @LastEditTime: 2021-08-21 16:32:54
 * @Description:
 * @Website: https://grimoire.cn
 * Copyright (c) NorthCityChen All rights reserved.
 */
package main

import (
    "fmt"
)

func main() {
    var s1, s2, s3, s4 = "Hello", "world", "my", "dears"
    s3, s4 = s4, s3 // 必须确保参与交换的变量数据类型相同
    fmt.Println(s1, s2, s3, s4)
}

值得注意的是，在golang中，string是不可修改的，因此尝试修改字符串内部的操作是被禁止的

package main

import "fmt"

func main() {
    str := "hello world"
    str[0] = "H" // cannot assign to str[0] (strings are immutable)
    fmt.Println(str)
}

这样的好处是，字符串类型的子字符串切片就不再需要花销额外的内存了