• 6.struct_types


    Declare, create and initialize struct types

    // Sample program to show how to declare and initialize struct types.
    
    package main
    
    import "fmt"
    
    // example represents a type with different fields.
    //示例表示具有不同字段的类型。
    
    type example struct {
    	flag    bool
    	counter int16
    	pi      float32
    }
    
    func main() {
    	// Declare a variable of type example set to its
    	// zero value.
    
    	var e1 example
    
    	//	display the value
    	fmt.Printf("%+v
    ", e1)
    
    	// Declare a variable of type example and init using
    	// a struct literal.
    
    	e2 := example{
    		flag:    true,
    		counter: 11,
    		pi:      3.14159,
    	}
    	// display the field values
    	fmt.Println("flag", e2.flag)
    	fmt.Println("counter", e2.counter)
    	fmt.Println("pi", e2.pi)
    
    	/*
    		{flag:false counter:0 pi:0}
    		flag true
    		counter 11
    		pi 3.14159
    	*/
    }
    
    

    Anonymous struct types

    package main
    
    import "fmt"
    
    func main() {
    	// Declare a variable of an anonymous type and init
    	// using a struct literal.
    	e := struct {
    		flag    bool
    		counter int16
    		pi      float32
    	}{
    		flag:    true,
    		counter: 10,
    		pi:      3.14159,
    	}
    
    	// Display the values.
    	fmt.Printf("%+v
    ", e)
    	fmt.Println("Flag", e.flag)
    	fmt.Println("Counter", e.counter)
    	fmt.Println("Pi", e.pi)
    	
    	/*
    	   {flag:true counter:10 pi:3.14159}
    	   Flag true
    	   Counter 10
    	   Pi 3.14159
    	*/
    }
    

    Named vs Unnamed types 命名类型和匿名类型

    // Sample program to show how variables of an unnamed type can
    // be assigned to variables of a named type, when they are
    // identical.
    package main
    
    import "fmt"
    
    // example represents a type with different fields.
    type example struct {
    	flag    bool
    	counter int16
    	pi      float32
    }
    
    func main() {
    	// Declare a variable of an anonymous type and init
    	// using a struct literal.
    	e := struct {
    		flag    bool
    		counter int16
    		pi      float32
    	}{
    		flag:    true,
    		counter: 10,
    		pi:      3.14159,
    	}
    
    	// Create a value of type example.
    	var ex example
    
    	// Assign the value of the unnamed struct type
    	// to the named struct type value.
    	// 分配未命名的struct类型的值。
    	// 到命名的struct类型值。
    	ex = e
    
    	// Display the values.
    	fmt.Printf("%+v
    ", ex)
    	fmt.Printf("%+v
    ", e)
    	fmt.Println("Flag", e.flag)
    	fmt.Println("Counter", e.counter)
    	fmt.Println("Pi", e.pi)
    	
    	
    /*
    
    {flag:true counter:10 pi:3.14159}
    {flag:true counter:10 pi:3.14159}
    Flag true
    Counter 10
    Pi 3.14159
    
    */	
    	
    }
    
    

    结构体类型排列

    // go get honnef.co/go/structlayout/cmd/...
    
    // Alignment is about placing fields on address alignment boundaries
    // for more efficient reads and writes to memory.
    
    // Sample program to show how struct types align on boundaries.
    // https://github.com/dominikh/go-tools/tree/master/cmd/structlayout
    // go get honnef.co/go/structlayout/cmd/...
    
    //对齐方式是在地址对齐边界上放置字段。
    //为了更有效地读写内存。
    
    //示例程序,以显示结构类型如何在边界上对齐。
    package main
    
    import (
    	"fmt"
    	"unsafe"
    )
    
    // No byte padding. 没有字节填充。
    type nbp struct {
    	a bool // 	1 byte				sizeof 1
    	b bool // 	1 byte				sizeof 2
    	c bool // 	1 byte				sizeof 3 - Aligned on 1 byte
    }
    
    // Single byte padding. 单个字节填充。
    type sbp struct {
    	a bool //	1 byte				sizeof 1
    	//			1 byte padding		sizeof 2
    	b int16 // 	2 bytes				sizeof 4 - Aligned on 2 bytes
    }
    
    // Two byte padding.
    type tbp struct {
    	a bool //	1 byte				size 1
    	//			3 bytes padding		size 4
    	b int32 //	4 bytes				size 8 - Aligned on 2 bytes
    }
    
    // Four byte padding.
    type fbp struct {
    	a bool //	1 byte				size 1
    	//			7 bytes padding		size 8
    	b int64 //	8 bytes				size 16 - Aligned on 8 bytes
    }
    
    // Eight byte padding on 64bit Arch. Word size is 8 bytes.
    // 在64位的Arch上有8个字节的填充。字大小是8个字节。
    type ebp64 struct {
    	a string //	16 bytes			size 16
    	b int32  //	 4 bytes			size 20
    	//  		 4 bytes padding	size 24
    	c string //	16 bytes			size 40
    	d int32  //	 4 bytes			size 44
    	//  		 4 bytes padding	size 48 - Aligned on 8 bytes
    }
    
    // No padding on 32bit Arch. Word size is 4 bytes.
    // To see this build as 32 bit: GOARCH=386 go build
    type ebp32 struct {
    	a string //	 8 bytes			size  8
    	b int32  //	 4 bytes			size 12
    	c string //	 8 bytes			size 20
    	d int32  //	 4 bytes			size 24 - Aligned on 4 bytes
    }
    
    // No padding.
    type np struct {
    	a string // 16 bytes			size 16
    	b string // 16 bytes			size 32
    	c int32  //  8 bytes			size 40
    	d int32  //  8 bytes			size 48 - Aligned on 8 bytes
    }
    
    func main() {
    	// structlayout -json github.com/ardanlabs/gotraining/topics/go/language/struct_types/advanced/example1 nbp | structlayout-pretty
    	var nbp nbp
    	size := unsafe.Sizeof(nbp)
    	fmt.Printf("SizeOf[%d][%p %p %p]
    ", size, &nbp.a, &nbp.b, &nbp.c)
    	/* SizeOf[3][0xc42001408a 0xc42001408b 0xc42001408c] */
    
    	// =========================================================================
    
    	// structlayout -json github.com/ardanlabs/gotraining/topics/go/language/struct_types/advanced/example1 sbp | structlayout-pretty
    	var sbp sbp
    	size = unsafe.Sizeof(sbp)
    	fmt.Printf("SizeOf[%d][%p %p]
    ", size, &sbp.a, &sbp.b)
    	/* SizeOf[4][0xc4200140c0 0xc4200140c2] */
    
    	// =========================================================================
    
    	// structlayout -json github.com/ardanlabs/gotraining/topics/go/language/struct_types/advanced/example1 tbp | structlayout-pretty
    	var tbp tbp
    	size = unsafe.Sizeof(tbp)
    	fmt.Printf("SizeOf[%d][%p %p]
    ", size, &tbp.a, &tbp.b)
    	/* SizeOf[8][0xc4200140d0 0xc4200140d4] */
    
    	// =========================================================================
    
    	// structlayout -json github.com/ardanlabs/gotraining/topics/go/language/struct_types/advanced/example1 fbp | structlayout-pretty
    	var fbp fbp
    	size = unsafe.Sizeof(fbp)
    	fmt.Printf("SizeOf[%d][%p %p]
    ", size, &fbp.a, &fbp.b)
    	/* SizeOf[16][0xc4200140e0 0xc4200140e8] */
    
    	// =========================================================================
    
    	// structlayout -json github.com/ardanlabs/gotraining/topics/go/language/struct_types/advanced/example1 ebp | structlayout-pretty
    	var ebp64 ebp64
    	size = unsafe.Sizeof(ebp64)
    	fmt.Printf("SizeOf[%d][%p %p %p %p]
    ", size, &ebp64.a, &ebp64.b, &ebp64.c, &ebp64.d)
    	/* SizeOf[48][0xc42007a180 0xc42007a190 0xc42007a198 0xc42007a1a8] */
    
    	// =========================================================================
    
    	// structlayout -json github.com/ardanlabs/gotraining/topics/go/language/struct_types/advanced/example1 np | structlayout-pretty
    	var np np
    	size = unsafe.Sizeof(np)
    	fmt.Printf("SizeOf[%d][%p %p %p %p]
    ", size, &np.a, &np.b, &np.c, &np.d)
    	/* SizeOf[40][0xc42007a1b0 0xc42007a1c0 0xc42007a1d0 0xc42007a1d4]  */
    }
    
    // https://github.com/ardanlabs/gotraining/tree/master/topics/go/language/struct_types
    
    
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  • 原文地址:https://www.cnblogs.com/zrdpy/p/8586513.html
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