What data types are there in go language?

The data types of go language are: 1. Boolean type; 2. Numeric type (can be divided into integer and floating point types); 3. String type; 4. Pointer type; 5. Array type; 6. Structured type; 7. Channel type; 8. Function type; 9. Slice type; 10. Interface type; 11. Map type.

The operating environment of this tutorial: Windows 10 system, GO 1.11.2, Dell G3 computer.

Go language is a statically typed programming language. In Go programming language, data types are used to declare functions and variables. The emergence of data types is to divide data into data with different memory sizes required. When programming, you need to apply for large memory only when you need to use big data, so that you can make full use of the memory. When the compiler compiles, it must know the type of each value, so that the compiler knows how much memory to allocate for this value, and what this allocated memory represents.

Basic data type description

##uint32-bit or 64-bituint8Unsigned 8 Bit integer type (0 to 255)uint16Unsigned 16-bit integer type (0 to 65535) uint32Unsigned 32-bit integer type (0 to 4294967295)uint64Unsigned 64-bit integer type (0 to 18446744073709551615)int32-bit or 64-bit int8Signed 8-bit integer (-128 to 127)int16Signed 16-bit integer (-32768 to 32767)int32Signed 32-bit integer (-2147483648 to 2147483647)int64Signed 64-bit integer (-9223372036854775808 to 9223372036854775807)byteuint8 alias (type byte = uint8) runeint32 alias (type rune = int32), represents a unicode code uintptr unsigned integer type, used to store a pointer is an unsigned integer type, no specific bit is specified size but large enough to accommodate pointers. float32IEEE-754 32-bit floating point number##float64complex64complex128

Integer type

Integer data is divided into two categories, signed and unsignedtwo types

Signed: int, int8, int16, int32, int64

Unsigned: uint, uint8, uint16, uint32, uint64, byte
Different bits The difference between the integer types of numbers is that they can store the size of the integer range;

The signed type can store any integer, and the unsigned type can only store natural numbers

The size of int and uint depends on the system , 32-bit system represents int32 and uint32, if it is a 64-bit system, it represents int64 and uint64

byte is similar to uint8, and is generally used to store a single character

To ensure that the program runs correctly, try to Use data types that occupy small space

fmt.Printf("%T", var_name) output variable type

unsafe.Sizeof(var_name) view the bytes occupied by variables

Floating point type

The floating point type is the decimal type and can store decimals. For example, 6.6, -12.34

1. A brief explanation of the storage form of floating point numbers in the machine. Floating point numbers = sign bit, exponent bit, mantissa bit

2. The mantissa part may be lost, resulting in loss of accuracy. . -123.0000901

package main

import "fmt"

func main() {
    
    var num1 float32 = -123.0000901
    var num2 float64 = -123.0000901
    fmt.Println("num1 = ", num1, "num2 = ", num2);
}

Note: The precision of float64 is more accurate than float32

Note: If we want to save a high-precision number, we should choose float64

3. The storage of floating point type is divided into three parts: sign bit, exponent bit, mantissa bit. During the storage process, the accuracy will be lost

4. The default floating point type of golang is float64 type

5. Under normal circumstances, float64 should be used because it is more accurate than float32

6. 0.123 can be abbreviated as .123, and it also supports scientific notation: 5.1234e2 is equivalent In 512.34

Character

There is no special character type in Golang. If you want to store a single character (letter), byte is generally used to save it.

A string is a sequence of characters connected by a fixed length of characters. Go's strings are connected by single bytes, which means that traditional strings are composed of characters, but Go's strings are different, they are composed of bytes.

• Characters can only be wrapped in single quotes, not double quotes. Double quotes wrap strings
• When we directly output the type value, the ASCII code of the corresponding character is output. Value
• When we want to output the corresponding characters, we need to use formatted output
• Go language characters use UTF-8 encoding, English letters occupy one character, and Chinese characters occupy three characters
• In Go, the essence of a character is an integer. When output directly, it is the UTF-8 encoding code value corresponding to the character.
• You can directly assign a number to a variable, and then when formatting the output %c will output the unicode character corresponding to the number
• The character type can be calculated and is equivalent to an integer , because they all have corresponding unicode codes

package main

import "fmt"

func main() {
    
    //字符只能被单引号包裹，不能用双引号，双引号包裹的是字符串
    var c1 byte = 'a'
    var c2 byte = '0'

    //当我们直接输出type值时，就是输出了对应字符的ASCII码值
    //'a' ==> 97
    fmt.Println(c1, "--", c2)
    //如果我们希望输出对应字符，需要使用格式化输出
    fmt.Printf("c2 = %c c2 = %c", c1, c2)
}

But if the characters we save are greater than 255, such as storing Chinese characters, the byte type cannot be saved. You can use uint or int type to save

Discussion on the essence of character type

• Character type is stored in the computer, and the code value corresponding to the character needs to be stored (Integer) Find out

  Storage: Character--> Code value--> Binary--> Storage

  Read: Binary-->Code value--> Characters --> Read

• The corresponding relationship between characters and code values ​​is determined by the character encoding table (it is specified)

• ## The encoding of #Go language is unified into UTF-8. It is very convenient and unified, and there is no longer the problem of garbled encoding

Boolean type

The Boolean type is also called the bool type. The bool type data only allows the value true Or false

The bool type occupies 1 byte

The bool type is suitable for logical operations and is generally used for process control

String

The string is A sequence of concatenated characters of a fixed length. Go's strings are concatenated from single bytes. The bytes of strings in Go language use UTF-8 encoding to identify Unicode text

1. Once a string is assigned a value, it cannot be modified:

Strings are immutable in Go.

2. Two identification forms of strings

• Double quotation marks will recognize escape characters

  var str = "abc\nabc" //输出时会换行

• Backticks, output in the native form of the string, including line breaks and special characters, can prevent attacks, output source code and other effects

  var str string = `abc\nabc` //输出时原样输出，不会转义

3. String splicing method" "

var str string = "hello " + "world"
str += "!"

4. When one line of string is too long and you need to use multiple lines of string, you can use the following processing

//正确写法
str := "hello" + 
	" world!"
fmt.Println(str)

//错误写法
str := "hello "
	+ "world!"
fmt.Println(str)

Pointer

• Basic data type, variables store values, also called value types

• To get the address of a variable, use &, such as var num int, to get the address of num:&num

• 指针类型，指针变量存的是一个地址，这个地址指向的空间存的才是值，比如:var ptr *int = &num

• 获取指针类型所指向的值，使用:*,比如,var ptr *int,使用*ptr获取ptr指向的值

指针细节说明:

• 值类型，都有对应的指针类型，形式为*数据类型，比如int对应的指针就是*int,float64对应的指针类型就是*float64,依此类推。

• 值类型包括:基本数据类型、数组和结构体struct

值类型与引用类型

值类型和引用类型使用特点:

值类型:变量直接存储值，内存通常在栈中分配

引用类型:变量存储的是一个地址，这个地址对应的空间才真正存储数据(值)，内存通常在堆上分配，当没有任何变量应用这个地址时，该地址对应的数据空间就成为一个垃圾，由GC来回收。

Golang中值类型和引用类型的区分

• 值类型:基本数据类型(int系列、float系列、bool、string)、数组和结构体

• 引用类型:指针、slice切片、map、管道chan、interface等都是引用类型

基本数据类型默认值

在Golang中，数据类型都有一个默认值，当程序员没有赋值时，就会保留默认值，在Golang中，默认值也叫做零值。

基本数据类型默认值如下:

Type	Description
	The uintptr type is only needed in low-level programming, especially where Go language interacts with C language function library or operating system interface.
IEEE-754 64-bit floating point number
32-bit real and imaginary number
64 Real and imaginary numbers

数据类型	默认值
整型	0
浮点型	0
字符串	""
布尔类型	false

package main

import "fmt"

func main() {
    
    var a int
    var b float32
    var isTrue bool
    var str string

    //这里的%v,表示按照变量的值输出
    fmt.Printf("a = %v, b = %v, isTrue = %v, str = %v", a, b, isTrue, str)
    fmt.Println("")
}

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