go学习第三天、数据类型

基本数据类型

bool
string
int int8 int16 int32 int64
uint uint8 uint16 uint32 uint64 uintptr
byte // alias for uint8
rune // alias for int32, represents a Unicode code point
float32 float64
complex64 complex128

类型转化

• Go语言不允许隐式类型转换
• 别名和原有类型也不能进行隐式类型转换

不允许隐式类型转换

package type_test

import "testing"

func TestImplicit(t *testing.T) {
    var a int = 1
    var b int64
    b = a
    t.Log(a, b)
}

输出

# command-line-arguments_test [command-line-arguments.test]
./type_test.go:10:4: cannot use a (type int) as type int64 in assignment

Compilation finished with exit code 2

修正后：

func TestImplicit(t *testing.T) {
    var a int = 1
    var b int64
    b = int64(a)

    t.Log(a, b)
}

输出

=== RUN   TestImplicit
--- PASS: TestImplicit (0.00s)
    type_test.go:12: 1 1
PASS

Process finished with exit code 0

别名和原有类型也不能进行隐式类型转换

func TestImplicit(t *testing.T) {
    var a int = 1
    var b int64
    b = int64(a)

    var c MyInt
    c = b
    t.Log(a, b, c)
}

输出

# command-line-arguments_test [command-line-arguments.test]
./type_test.go:13:4: cannot use b (type int64) as type MyInt in assignment

Compilation finished with exit code 2

修正后

func TestImplicit(t *testing.T) {
    var a int = 1
    var b int64
    b = int64(a)

    var c MyInt
    c = MyInt(b)
    t.Log(a, b, c)
}

输出

=== RUN   TestImplicit
--- PASS: TestImplicit (0.00s)
    type_test.go:14: 1 1 1
PASS

Process finished with exit code 0

类型的预定义值

1. math.MaxInt64 最大能表示的最大整型
2. math.MaxFloat64 最大能表示的浮点型
3. math.MaxUint32 最大能表示32位无符号整型

指针类型

1. 不支持指针运算
2. string是只类型，其默认的初始化值为空字符串，而不是nil

不支持指针运算

func TestPoint(t *testing.T) {
    a := 1
    aPtr := &a
    aPtr = aPtr + 1
    t.Log(a, aPtr)
    t.Logf("%T %T", a, aPtr)
}

输出

# command-line-arguments_test [command-line-arguments.test]
./type_test.go:20:14: invalid operation: aPtr + 1 (mismatched types *int and int)

Compilation finished with exit code 2

string是只类型，其默认的初始化值为空字符串，而不是nil

func TestString(t *testing.T)  {
    var s string
    t.Log("*"+s+"*")
    t.Log(len(s))
    if len(s)==0{
        t.Log("这是一个空字符串")
    }
}

输出

=== RUN   TestString
--- PASS: TestString (0.00s)
    type_test.go:27: **
    type_test.go:28: 0
    type_test.go:30: 这是一个空字符串
PASS

Process finished with exit code 0