Go语言高性能字符串拼接

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所以,如果我在不知道结果是多少长字符串的情况下不断的连接字符串,怎么样的方式是最好的呢?

1. 方法一:使用strings.Builder

从Go 1.10(2018)版本开始可以使用 strings.Builder ,

A Builder is used to efficiently build a string using Write methods. It minimizes memory copying. The zero value is ready to use. Do not copy a non-zero Builder.

strings.Builder 使用 Write 方法来高效的构造字符串. 它使用内存最小,它使用零值,它不拷贝零值. 注意: 不要拷贝strings.Builder的值,如果你要使用strings.Builder值请使用pointer 使用方法,代码如下:

package main
import (
    "strings"
    "fmt"
func main() {
    var str strings.Builder
    for i := 0; i < 1000; i++ {
        str.WriteString("a")
    fmt.Println(str.String())

2. 方法二:使用bytes.Buffer

在201X年之前使用 bytes 包的 Buffer 它实现了 io.Writer 的接口,使用他来拼接字符串.他的事件复杂度 O(n) .

package main
import (
    "bytes"
    "fmt"
func main() {
    var buffer bytes.Buffer
    for i := 0; i < 1000; i++ {
        buffer.WriteString("a")
    fmt.Println(buffer.String())

3. 方法三:使用go语言内置函数copy

Go内建函数copy: func copy(dst, src []Type) int , 用于将源slice的数据（第二个参数）,复制到目标slice（第一个参数）. 返回值为拷贝了的数据个数,是len(dst)和len(src)中的最小值.

package main
import (
    "bytes"
    "fmt"
func main() {
    bs := make([]byte, 1000)
    bl := 0
   for n := 0; n < 1000; n++ {
        bl += copy(bs[bl:], "a")
    fmt.Println(string(bs))

4. 方法四:使用go语言内置函数append

append主要用于给某个切片（slice）追加元素, 如果该切片存储空间（cap）足够，就直接追加，长度（len）变长；如果空间不足，就会重新开辟内存，并将之前的元素和新的元素一同拷贝进去, 第一个参数为切片，后面是该切片存储元素类型的可变参数,

package main
import (
    "bytes"
    "fmt"
func main() {
    bs := make([]byte, 1000)
   for n := 0; n < 1000; n++ {
        bs = append(bs,'a')
    fmt.Println(string(bs))

5. 方法五: 使用字符串+运算

package main
import (
    "fmt"
func main() {
    var result string
    for i := 0; i < 1000; i++ {
            result += "a"
    fmt.Println(result




    
)

6. 方法六: strings.Repeat

strings.Repeat 将 count 个字符串 s 连接成一个新的字符串

package main
import (
    "fmt"
    "strings"
func main()  {
    fmt.Println(strings.Repeat("x",1000))

strings.Repeat它的底层调用的是strings.Builder,提前分配了内存.

// Repeat returns a new string consisting of count copies of the string s.
// It panics if count is negative or if
// the result of (len(s) * count) overflows.
func Repeat(s string, count int) string {
    if count == 0 {
        return ""
    // Since we cannot return an error on overflow,
    // we should panic if the repeat will generate
    // an overflow.
    // See Issue golang.org/issue/16237
    if count < 0 {
        panic("strings: negative Repeat count")
    } else if len(s)*count/count != len(s) {
        panic("strings: Repeat count causes overflow")
    n := len(s) * count
    var b Builder
    b.Grow(n)
    b.WriteString(s)
    for b.Len() < n {
        if b.Len() <= n/2 {
            b.WriteString(b.String())
        } else {
            b.WriteString(b.String()[:n-b.Len()])
            break
    return b.String()

7. Benchmark

string_benchmark.go

package main
import (
    "bytes"
    "strings"
    "testing"
const (
    sss = "https://mojotv.cn"
    cnt = 10000
var (
    bbb      = []byte(sss)
    expected = strings.Repeat(sss, cnt)
//使用 提前初始化  内置 copy函数
func BenchmarkCopyPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        bs := make([]byte, cnt*len(sss))
        bl := 0
        for i := 0; i < cnt; i++ {
            bl += copy(bs[bl:], sss)
        result = string(bs)
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 提前初始化  内置append 函数
func BenchmarkAppendPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, cnt*len(sss))
        for i := 0; i < cnt; i++ {
            data = append(data, sss...)
        result = string(data)
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 提前初始化 bytes.Buffer
func BenchmarkBufferPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        buf := bytes.NewBuffer(make([]byte, 0, cnt*len(sss)))
        for i := 0; i < cnt; i++ {
            buf.WriteString(sss)
        result = buf.String()
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 strings.Repeat 本质是pre allocate + strings.Builder
func BenchmarkStringRepeat(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        result = strings.Repeat(sss,cnt)
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 内置copy
func BenchmarkCopy(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, 64) // same size as bootstrap array of bytes.Buffer
        for i := 0; i < cnt; i++ {
            off := len(data)
            if off+len(sss) > cap(data) {
                temp := make([]byte, 2*cap(data)+len(sss))
                copy(temp, data)
                data = temp
            data = data[0 : off+len(sss)]
            copy(data[off:], sss)
        result = string(data)
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 内置append
func BenchmarkAppend(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, 64)
        for i := 0; i < cnt; i++ {
            data = append(data, sss...)
        result = string(data)
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 bytes.Buffer
func BenchmarkBufferWriteBytes(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf bytes.Buffer
        for i := 0; i < cnt; i++ {
            buf.Write(bbb)
        result = buf.String()
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 strings.Builder write bytes
func BenchmarkStringBuilderWriteBytes(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf strings.Builder
        for i := 0; i < cnt; i++ {
            buf.Write(bbb)
        result = buf.String()
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
//使用 string buffer write string
func BenchmarkBufferWriteString(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf bytes.Buffer
        for i := 0; i < cnt; i++ {
            buf.WriteString(sss)
        result = buf.String()
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
// 使用string 加号
func BenchmarkStringPlusOperator(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var str string
        for i := 0; i < cnt; i++ {
            str += sss
        result = str
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)

执行 go test -bench=. -benchmem 输出结果:

$ go test -bench=. -benchmem
goos: windows
goarch: amd64
BenchmarkCopyPreAllocate-8                 10000            117600 ns/op          344065 B/op          2 allocs/op
BenchmarkAppendPreAllocate-8               20000             75300 ns/op          344065 B/op          2 allocs/op
BenchmarkBufferPreAllocate-8               20000             97149 ns/op          344065 B/op          2 allocs/op
BenchmarkStringRepeat-8                   100000             18349 ns/op          172032 B/op          1 allocs/op
BenchmarkCopy-8                            10000            152417 ns/op          862307 B/op         13 allocs/op
BenchmarkAppend-8                          10000            157210 ns/op         1046405 B/op         23 allocs/op