Go study notes

Golang

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preface

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1, Golang environment

1. Directory structure

2. Code structure

go build test.go compile go file to generate exe file
test.exe

go run is equivalent to two steps, compiling and executing

2, Golang Foundation

1.Go execution process analysis

The code is as follows (example):

One can generate an EXE file and then execute the exe.

The compiled file will be larger because some dependent library files are put into the executable file

The second can be compiled and run directly.

The difference is that the first method can execute exe on a machine without go development environment.

2. Syntax considerations

If the imported package is not used, go build will fail.

3. Code style

4.API (source code search)

5. Variables

package main import "fmt" func main() { var age int age = 18 fmt.Print(age) } Declaring a variable is equivalent to opening up a space in memory for it

A. Four forms of use

Global variable declaration

6. Basic data type

A. Integer type

I. signed integer type

package main import "fmt" func main() { var num int8 = 321 fmt.Println(num) } D:\gowork\src\unit2\demo01>go build main.go # command-line-arguments .\main.go:12:6: constant 321 overflows int8

II. Unsigned integer type

Golang's default integer type is int

III. other integer types

%T View type func main() { var num3 = 28 fmt.Printf("%T", num3) fmt.Println() fmt.Println(unsafe.Sizeof(num3)) } D:\gowork\src\unit2\demo01>main.exe int 8

For example, in java, it is normal to use int for age. In fact, int takes up too much byte space. You can use byte.
Use uint8 in go, unsigned bit int 0 - 255

B. Floating point type

Floating point underlying storage space is independent of the operating system
The bottom storage of floating-point type: sign bit + exponential bit + mantissa. Only the mantissa position is stored, and there may be precision loss

func main() { var num float32 = 314e-2 //That's 314 times 10 to the negative quadratic fmt.Println(num) var num1 float32 = 314e+2 //That's 314 times 10 to the power of two fmt.Println(num1) var num2 float32 = 256.0000000916 fmt.Println(num2) } D:\gowork\src\unit2\demo01>main.exe 3.14 31400 256 You can see that the accuracy is lost The default type is float64

C. Character type

func main() { var c1 byte = 'a' fmt.Println(c1) var c2 byte = '6' fmt.Println(c2) var c3 byte = '(' fmt.Println(c3) } ASCII code D:\gowork\src\unit2\demo01>main.exe 97 54 40

D.Boolean type

E. String type

Escape double quotes with special characters

F. Default value of basic data type

G. Explicit conversion of data type

n1 above is still of type int, but the value of n1 is converted to float32

Data overflow when converting large type to small type

When adding multiple data types, pay attention to the consistency of data types

+128 exceeds the range of int8

H. Data type to String

fmt.Sprintf(%？ n)
%？ Data type corresponding to n

1. String to basic data type

Ignore err errors.

7. Complex data types

A. Pointer

&age
View variable memory address

func main() { var age int = 15 fmt.Println(&age) //var stands for declared variable //ptr pointer variable name //*Int pointer type (pointer to int type) //&Age memory address var ptr *int = &ag }