This is the fourth day of my participation in the August Challenge. For details, see:August is more challenging

ptr

Pointers in GO have two core concepts

• A pointer to a type that allows modification of data of this type. Data can be passed directly to the pointer without copying the data. A pointer to a type cannot be offset or manipulated.
• Slice, consisting of the original pointer to the starting element, the number of elements, and the capacity.

Pointer address and pointer type

• Pointer address, each pointer variable, which stores the memory address of the value. In other words, this memory address takes up 4 bytes of space on a 32-bit machine and 8 bytes of space on a 64-bit machine. The size of this memory address does not matter
• Pointer type,

Get pointer address “&”

ptr := &aaa

Where aaa is a value and PTR is the assigned pointer argument

Get the value “*” of the pointer

str := *ptr

Use * to get the contents of the value to which the pointer points

Assign and get the value of a pointer

Package main import "FMT" func main() {var cat string = "I love egg fried rice" catAddress := &cat catValue := *catAddress Println("", &cat, catAddress, catValue)} 0x14000010240 0x14000010240 I love egg-fried riceCopy the code

The address operator & and the value operator * are a pair of complementary operators. & retrieves the address, and * retrieves the value that the address points to based on the address.

Modify the value of the pointer

Package main import "FMT" func main() {var cat string = "I love egg fried rice" catAddress := &cat catValue := *catAddress fmt.Println("", &cat, catAddress, catValue) a:=1 b:=2 swap(&a,&b) fmt.Println("",a,b) } func swap(a, b *int) { t := *a *a = *b *b = t }Copy the code

Another way to create a pointer

New (type)

Println(* STR) :=new (string) * STR = FMT.Println(* STR)Copy the code

Usage scenarios of Pointers

1. Direct manipulation of the address to which the pointer points completely changes the value of the parameter, so it can be used in method passing. The input parameter of the direct method is passed a pointer type of the parameter, and the parameter is changed in the method. It will cause the caller to change it as well so the usual function argument list is*xxxAs a parameter

package main

import (
	"errors"
	"fmt"
)

func testMap(strs *[]string) (bool, error) {

	for _, str := range *strs {

		fmt.Println(str)
	}
	*strs = append(*strs, "Black")
	return true, errors.New("No error result information.")}func main(a) {
	strs := []string{"White"."Little red"."Little blue"}
	b, err := testMap(&strs)

	fmt.Printf("", b, err)
	fmt.Printf("", strs)
}

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Conditional statements

if

use

If a < 20 {/* if a < 20 {/* if the condition is true, execute the following statement */ fmt.printf ("a < 20\n")}Copy the code

switch

Switch {case grade == "A" : FMT.Printf(" 高 级! \n") case grade == "B", grade == "C" : FMT.Printf(" good \n") case grade == "D" : FMT.Printf(" good \n") case grade == "F": FMT.Printf(" fail \n") default: FMT.Printf(" fail \n"); }Copy the code

select

Select randomly executes a runnable case. If there are no cases to run, it blocks until there are cases to run. A default clause should always run.

   select {
      case i1 = <-c1:
         fmt.Printf("received ", i1, " from c1\n")
      case c2 <- i2:
         fmt.Printf("sent ", i2, " to c2\n")
      case i3, ok := (<-c3):  // same as: i3, ok := <-c3
         if ok {
            fmt.Printf("received ", i3, " from c3\n")
         } else {
            fmt.Printf("c3 is closed\n")
         }
      default:
         fmt.Printf("no communication\n")
   }
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Looping statements

for

Three ways of use

1. For numerical initialization; Cycle judge; Numerical transformation {logical processing}Consistent with forI in Java

    for i := 0; i <= 10; i++ {
                sum += i
    }
   Copy the code

2. For loop judge {logical statement (where numerical transformation is performed)}Assign a value before use. That is, divide the first method into three pieces

        sum := 1
        for ; sum <= 10; {
                sum += sum
        }
   Copy the code

3. for { }

   Sum := 0 for {sum++}Copy the code

break; Statement breaks the current for loop or breaks out of the switch loop

continue; Statement to jump out of the current cycle and proceed to the next cycle

Function/method

Definition of a function

structure

Func method name ([parameter list]) [return value type] {logical processing}Copy the code

For example,

Func mulit100(val *int32) (bool,error){val=val*100 return (true, errors.new (" no error message returned "))}Copy the code

Parameter list and return value types are not required

Calling a function

Return value Result = Function name (argument list)Copy the code

Built-in function

Anonymous functions

func(a) {// Define an anonymous
    //func body} ()// The curly braces are followed by () to indicate a function call.
Copy the code