variable definition
basic method:
var variableName typevar person string
multiple variable definition:
var vname1, vname2, vname3 type
define the variable and initialize it:
var variableName type = value
initialize multiple variables:
var vname1, vname2, vname3 type = v1, v2, v3
or simplify it:
var vname1, vname2, vname3 = v1, v2, v3
or do the most simplified one:
vname1, vname2, vname3 := v1, v2, v3
Noted that this version should only be adopted inside the functions, or the complation will fail.
So the definition withe the prefix
varcan be used for the global variables._ is a special variable name, all values allocated to it will be deprecated
_, b := 34, 35
Declared but not used variables will trigger mistakes, which is not permmited in go.
Const
Const are those whose values have been determined when compiling.
const constantName = value//if necessary, allocate the type of the constconst Pi float32 = 3.1415926const prefix = "astaxie_"
Other types
Boolean, int, uint, int8, int16, int32, int64, byte, uint8, uint16, uint32, uint64, float32, float64
rune is equivalent to int32, byte is equivalent to uint8.
int's lenth is 32, but it is not equal to int32.
No float, the deflaut one is float64
complex is supported, complex128(64+64i) and complex64(32+32i)
var c complex64 = 5+5ifmt.Printf("Value is: %v",c)
String
Use ""or to define the String in between.
var frenchHello stringvar emptyString string = ""func test(){ no, yes, maybe := "no", "yes", "maybe" japaneseHello := "Konichiwa" frenchHello := "Bonjour"}
Noted that string is not changable
var s string = "hello"s[0] = 'c'//raise mistake "cannot assign to s[0]"here is the method to do the modification
s := "hello"c := []byte(s) //convert s to []bytec[0] = 'c's2 := string(c) //convert it backOr use slice to modify the string
s := "hello"h := "c" + s[1:]fmt.Printf("%s\n",h)
+ can connect two strings together
s := "hello"h := "world"a := s+hfmt.Printf("%s\n",a)
can preserve the initial format of the string, all things will remain the same.
m := `Hello World`fmt.Printf("%s\n",m)
Here is the output:
Hello World
Error
The type of error is specially for handling mistakes. There us a package of errors.
err := errors.New("emit macho dwarf: elf header corrupted")if err != nil{ fmt.Printf(err)}
Storage of data
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Some skills
- declaration by groups
import( "fmt" "os")const( i = 100 pi = 3.1415 prefix = "Go_")var ( i int pi float32 prefix string)
- iota enumeration
One more lines of const, one more the value of iota
package mainimport ( "fmt")const ( x = iota //x = 0 y = iota //y = 1 z //z = 2, with omission declaration)const v = iota //one more keyword const, reset the value of iotaconst ( h,j,i = iota,iota,iota //all is 0, three should match three)const ( a = iota //a = 0 b = "B" c,d,e = iota //c,d,e = 1)
Default rules
variables with capital letter are public, other packages could read the value, variables with lowercase letters are private.
Same as the fuction names.
array
Declaration
var arr [n]type
n is the length of the array, type is the elements this array stores,
var arr [10]intarr[0] = 42arr[1] = 13fmt.Println(arr[9]) //The initial value of a[9] is 0
Declaration inside the functions:
a := [3]int{1,2,3}b := [10]int{1,2,3}c := [...]int{4,5,6} //omit the length, count the number of elements instead
Matraix:
doubleArray := [2][4]int{ {1,2,3,4} {5,6,7,8}}
Noted that when we pass one array into the function, we pass the copy of this array rather than its pointer.
if you wanted to modify the elements anyway, use slice.
Slice
Or could be described as "dynamical array", do not need the specification of length.
var fslice []int
Initialization:
slice := []byte {'a','b','c'}
slice could be picked from an existed array by array[i:j], array[i] is included, array[j] is excluded, the length is j-i
var ar = [10]int {1,2,3,4,5,6,7,8,9,10}var a, b []inta = ar[2,5]b = ar[3,5]
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When changing the values in the slice, the corresponding value in the array will be changed,too.
The interfaces in slice:
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lencan get the lengthcapcan get the capacityappendcan add one or more elements and return theslice
capacity could be specified now:
slice = array[2:4:7] //capacity is 7-2
map
The dictionary in Python, whose index could be many types besides int.
Noted that the declaration should be outside the function, while the memory allocation should be inside the function.
var numbers map[string]int //declaration, should initialize it by make afterwardsnumbers = make(map[string]int)numbers["one"] = 1numbers["two"] = 2
map is unordered, which should be acquired by
keyrather thanindexmap has two return, the first one is the value, the second one is the boolean
rating := map[string]float32{"C":5,"Go":4.5,"Python":4.5}csharpRating, ok := rating["C#"]if ok{ fmt.Println("C# is in the map and its rating is ", cssharpRating)}delete(rating, "C#")
Differences between make and new
make: allocate memory for
map,slice,channel,return T type rather than *T.new: allocate memory for various types, the default value is 0, return *T(its address) pointingto T's value
Zero values
int 0int8 0int32 0int64 0uint 0x0rune 0 //rune的实际类型是 int32byte 0x0 // byte的实际类型是 uint8float32 0 //长度为 4 bytefloat64 0 //长度为 8 bytebool falsestring ""
The default padding values when you new the type
