go-Study Notes

June 30, 2018

Basic commands

1. Go build is used to compile source files, code packages, dependency packages

The path to the executable file is$GOPATH/bin

2. Go run to compile and run the Go source file
3. Go get dynamic Get Remote code package

System keyword or reserved word

1, reserved keywords

Break	Default	Func	Interface	Select
Case	Defer	Go	Map	struct
Chan	Else	Goto	Package	Switch
Const	Fallthrough	If	Range	Type
Continue	For	Import	Return	Var

2, the predetermined identifier, including the underlying data type and the system inline function.

Append	bool	Byte	Cap	Close	Complex
Complex64	complex128	UInt16	Copy	False	Float32
Float64	Imag	Int	int8	Int16	UInt32
Int32	Int64	Iota	Len	Make	New
Nil	Panic	UInt64	Print	println	Real
Recover	String	True	UInt	Uint8	Uintprt

3, inline data type

• Boolean type:

  • The system defines two constants for this type: true and false.

  • The initial default value is: false.

  • Format the output when the format string is:%t.

  • Instance code:

    • Image

  • The output is:

    • Flag1 = True
    • !flag1 = False
    • GlobalFlag = True
    • (Flag1 && Flag2) = False
    • (Flag1 | | flag2) = True

• BYTE type:

  • For Uint8, that is, there are only 8 bit.

• Number type:

  • Integer type:

    • Signed integers: int8, Int16, Int32, Int64, and int (this type may vary depending on the specific platform)

    • unsigned integers: uint8, uint16, UInt32, UInt64, and uint (this type may vary depending on the specific platform)

    • The initial default value is: 0.

    • Format the output when the format string is:%d, output 16:%x or%x;8 binary:%o.

    • Instance code:

      • Image

    • The output is:

      • I8=9, i=27, ui32=30, ui64=40, defint=0

      • i8=11, i=1b, ui32=1e, ui64=101000

      • The value=27, the address=0x117d0238

  • Floating-point types: float32 and Float64

    • The initial default value is: 0.0.

    • Note: There is no type of float and you cannot use = = and! = When comparing two floating-point numbers

    • Format the output when the format string is:%g,%f corresponds to a pointer to a floating-point type; the%e corresponds to the scientific counter-prosecute output;%N.MG is used to specify the decimal output.

    • Instance code:

      • Image

    • Output Result:

      • F32 = 2.054545, f64=4.054544925689697, default=0
      • F32 = 2.05
  • Plural type:

    • Complex64: Both real and imaginary are 32 bits

    • COMPLEX128: Both real and imaginary are 64 bits

    • Real (c): Get the real number part

    • Imag (c): Obtaining imaginary parts

    • Format the output when the format string is:%v, you can also use%f to output real and imaginary parts.

    • Instance code:

      • Image

    • Output Result:

      • The com1= (2+3i), the com2= (3+4i)
      • The com2= (5+7i)
      • The real of com2=5, the imag of com2=7

• Character type:

  • Strictly speaking, there is no such type in go, it is a special integer type.
  • It corresponds to the uint8 type, which corresponds to the traditional ASCII code, which accounts for 1byte.
  • Unicode (UTF-8) encoding is also supported, so it may point to multiple bytes, known as Unicode code points or runes. At this point it corresponds to the number type of the Int32.
  • Enclosed in single quotation marks.
  • Unicode characters are usually represented in 16-binary form (\u+4 or \u+8)
  • Format the output when the format string is:%c;%v or%d displays the corresponding integer value;%u output: u+hhhh

• String type:

  • A string of UTF-8 encoded characters (which may account for 1~4byte)----characters in Java are 2bytes.
  • Enclosed in double quotes, only in a separate line. (interpreted string)
  • Enclosed in anti-quotes, you can span multiple lines. (Raw String)
  • Note: Go all the code is UTF-8 format, so there is no character encoding and decoding.
  • It is an immutable value type, so you cannot modify the string directly.

• Pointer type:

  • is 4byte in size.
  • Each data type has a corresponding pointer type.
  • Declaring a method is similar to the declaration of a pointer in C: *type.

4 operator

• Logical operators:
  • With: &&, or: | |, non:!.
  • ==,!=,<,>,<=,>=
• Bitwise operators:
  • can only work on variables of type int.
  • Bitwise vs: &, bitwise OR: |, bitwise XOR: ^
  • Shift left: <<, move right:>>. (Vacancy 0)
• Arithmetic operators:
  • +,-,*,/.
  • Modulus:%
  • Simplified operation:-=,*=, + =,%=
  • + +,--。 (only after the number variable, not at the beginning, which is not the same as C,java).
• Priority: (7-1: From high to low)

Global variables
Outside of the Func
Local variables
Within the Func

Source file Template

package main// 程序所属包import "fmt"//导入依赖包const NAME string = "SoulMO"//定义常量var a string = "Golang学习"//声明全局变量及赋值type GoLearntInt int//一般类型声明type Learn struct{}//结构体声明type ILearn interface {    }//声明接口func GoLearn()  {    fmt.Println(a,"learn Golang")}//定义函数func main() {    GoLearn();    fmt.Println(a,"Hello ~")}// main函数

Basic syntax

1, Package

• Package is the most basic distribution unit and the embodiment of dependency in engineering management
• Each Golang source code file has a package declaration that indicates the source code file belongs to the code bundle
• To generate the Golang executable, you must have the package of main, and the package must have main ()
• Only one package can exist under the same path, and a single one may consist of multiple source code files

Package name is the current folder name to avoid confusion

2,import

• Import is imported according to order
  Function name must start with uppercase

3 Type 0 Value
Value type defaults to 0
Boolean type defaults to False
string defaults to an empty string

3, parameter declaration initialization and assignment
Variable declaration format
var <变量名称> [变量类型]
Variable assignment format
<变量名称> = <值，表达式，函数等>
Variable declaration and assignment format
var <变量名称> [变量类型] = <值，表达式，函数等>
Group Declaration format

var(  i int  j float32  name string)

Single-line declaration of multiple variables and assignments
var a, b, c int = 1, 2, 3Ora, b := 1, 2
Global variable declaration must be var, local variable can be omitted
Special variable Underline "_";
Assigning a value to "_" means that the value is destroyed, and the next operation will not be able to invoke the value

The go-type conversion must be explicit
Type conversions can only occur between two compatible types
Type conversion format<变量名称> [:]= <目标类型>

A variable that starts with a capital letter is a common variable that can be called by another package read
A variable is a private variable that starts with a lowercase letter and can only be used by the current package