我想替换字符串中特定索引处的字母：aaaaaaa - ＆gt; aaabaaa。有没有内置的方法来做到这一点？我编写了以下辅助函数来同时使用：
func main() {
input := "aaaaaaa"
output := replaceAtIndex(input, 'b', 3)
}
func replaceAtIndex(input string, replacement byte, index int) string {
return strings.Join([]string{input[:index], string(replacement), input[index+1:]}, "")
}
答案 0 :(得分：18)
字符串在Go中是不可变的，你必须将其转换为符文然后修改它然后将其转换回字符串。
@ chendesheng的解决方案是半正确的，除了你可以使用rune而不是byte，这样它也可以用于unicode。
func replaceAtIndex(in string, r rune, i int) string {
out := []rune(in)
out[i] = r
return string(out)
}
答案 1 :(得分：14)
两个答案（ OneOfOne 和DenysSéguret）都是正确的。我只想展示它们之间的性能差异（当字符串很大时这是非常明显的）。
事实证明，使用 str [：index] + string（替换）+ str [index + 1：] 会更快。
所以基准：
package main
import (
"testing"
)
func replaceAtIndex1(str string, replacement rune, index int) string {
out := []rune(str)
out[index] = replacement
return string(out)
}
func replaceAtIndex2(str string, replacement rune, index int) string {
return str[:index] + string(replacement) + str[index+1:]
}
func generateString(n int) string{
s := ""
for i := 0; i < n; i++{
s += "a"
}
return s
}
func BenchmarkSmall1(b *testing.B) {
n := 10
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex1(str, replacement, index)
}
}
func BenchmarkSmall2(b *testing.B) {
n := 10
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func BenchmarkMedium1(b *testing.B) {
n := 100
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex1(str, replacement, index)
}
}
func BenchmarkMedium2(b *testing.B) {
n := 100
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func BenchmarkBig1(b *testing.B) {
n := 10000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex1(str, replacement, index)
}
}
func BenchmarkBig2(b *testing.B) {
n := 10000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func main(){}
显示以下结果（感谢Thomasz发现了一个copypasting错误）：
BenchmarkSmall1-4 10000000 228 ns/op
BenchmarkSmall2-4 10000000 126 ns/op
BenchmarkMedium1-4 500000 2091 ns/op
BenchmarkMedium2-4 10000000 190 ns/op
BenchmarkBig1-4 10000 209232 ns/op
BenchmarkBig2-4 500000 3629 ns/op
答案 2 :(得分：8)
您可以使用+运算符连接字符串：
return input[:index] + string(replacement) + input[index+1:]
答案 3 :(得分：2)
只是为了好玩：
package main
import (
"fmt"
"reflect"
"syscall"
"unsafe"
)
// We should do this because by default strings in Go are read-only.
func mprotect(ptr uintptr, w bool) {
// Need to avoid "EINVAL addr is not a valid pointer,
// or not a multiple of PAGESIZE."
start := ptr & ^(uintptr(syscall.Getpagesize() - 1))
prot := syscall.PROT_READ
if w {
prot |= syscall.PROT_WRITE
}
_, _, err := syscall.Syscall(
syscall.SYS_MPROTECT,
start, uintptr(syscall.Getpagesize()),
uintptr(prot),
)
if err != 0 {
panic(err.Error())
}
}
// This function is very, very very very unsafe.
// Nowhere and never use it!
func replaceAtIndex(s string, b byte, i int) {
h := *(*reflect.StringHeader)(unsafe.Pointer(&s))
mprotect(h.Data, true)
defer mprotect(h.Data, false)
*(*byte)(unsafe.Pointer(h.Data + uintptr(i))) = b
}
func main() {
h := "Hello, playground"
replaceAtIndex(h, 'x', 0)
fmt.Println(h)
}
永远不要尝试在代码中的某处使用它。 它比上面的任何标准解决方案或示例慢，而且更不安全。 =）
（它不在游乐场工作，因为那里没有定义syscall）。
答案 4 :(得分：0)
我采用了萨尔瓦多的基准，并添加了strings.Join()。他的答案仍然正确-假设您想保留原始字符串，str[:index] + string(replacement) + str[index+1:]是大型字符串的最快选择。 strings.Join()非常适合小字符串，非常适合大字符串。我还添加了包含更大字符串的测试，以查看strings.Join()在任何时候是否变得更快-似乎没有。
我也只是出于娱乐目的，用unsafe和reflect入侵了另外两个实现
我还必须修改generateString()，以便它将在合理的时间范围内生成最大的字符串;）
无论如何，代码：
package main
import (
"reflect"
"strings"
"testing"
"unsafe"
)
func replaceAtIndex1(str string, replacement rune, index int) string {
out := []rune(str)
out[index] = replacement
return string(out)
}
func replaceAtIndex2(str string, replacement rune, index int) string {
return str[:index] + string(replacement) + str[index+1:]
}
func replaceAtIndex3(str string, replacement rune, index int) string {
return strings.Join([]string{str[:index], str[index + 1:]}, string(replacement))
}
func strToBytes(str string) []byte {
string_header := (*reflect.StringHeader)(unsafe.Pointer(&str))
bytes_header := &reflect.SliceHeader{
Data : string_header.Data,
Len : string_header.Len,
Cap : string_header.Len,
}
return *(*[]byte)(unsafe.Pointer(bytes_header))
}
func strToBytesCopy(str string) []byte {
bytes_unsafe := strToBytes(str)
bytes := make([]byte, len(bytes_unsafe))
copy(bytes, bytes_unsafe)
return bytes
}
func bytesToStr(bytes []byte) string {
bytes_header := (*reflect.SliceHeader)(unsafe.Pointer(&bytes))
string_header := &reflect.StringHeader{
Data : bytes_header.Data,
Len : bytes_header.Len,
}
return *(*string)(unsafe.Pointer(string_header))
}
func replaceAtIndex4(str string, replacement rune, index int) string {
bytes := strToBytesCopy(str)
bytes[index] = byte(replacement)
return bytesToStr(bytes)
}
func replaceAtIndex5(str string, replacement rune, index int) string {
bytes := strToBytes(str)
bytes[index] = byte(replacement)
return bytesToStr(bytes)
}
func generateString(n int) string{
var b strings.Builder
b.Grow(n)
for i := 0; i < n; i++ {
b.WriteRune('a')
}
return b.String()
}
func BenchmarkSmall1(b *testing.B) {
n := 10
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex1(str, replacement, index)
}
}
func BenchmarkSmall2(b *testing.B) {
n := 10
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func BenchmarkSmall3(b *testing.B) {
n := 10
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex3(str, replacement, index)
}
}
func BenchmarkSmall4(b *testing.B) {
n := 10
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex4(str, replacement, index)
}
}
func BenchmarkSmall5(b *testing.B) {
n := 10
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex5(str, replacement, index)
}
}
func BenchmarkMedium1(b *testing.B) {
n := 100
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex1(str, replacement, index)
}
}
func BenchmarkMedium2(b *testing.B) {
n := 100
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func BenchmarkMedium3(b *testing.B) {
n := 100
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex3(str, replacement, index)
}
}
func BenchmarkMedium4(b *testing.B) {
n := 100
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex4(str, replacement, index)
}
}
func BenchmarkMedium5(b *testing.B) {
n := 100
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex5(str, replacement, index)
}
}
func BenchmarkBig1(b *testing.B) {
n := 10000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex1(str, replacement, index)
}
}
func BenchmarkBig2(b *testing.B) {
n := 10000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func BenchmarkBig3(b *testing.B) {
n := 10000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex3(str, replacement, index)
}
}
func BenchmarkBig4(b *testing.B) {
n := 10000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex4(str, replacement, index)
}
}
func BenchmarkBig5(b *testing.B) {
n := 10000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex5(str, replacement, index)
}
}
func BenchmarkHuge2(b *testing.B) {
n := 100000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func BenchmarkHuge3(b *testing.B) {
n := 100000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex3(str, replacement, index)
}
}
func BenchmarkHuge4(b *testing.B) {
n := 100000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex4(str, replacement, index)
}
}
func BenchmarkHuge5(b *testing.B) {
n := 100000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex5(str, replacement, index)
}
}
func BenchmarkGargantuan2(b *testing.B) {
n := 10000000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex2(str, replacement, index)
}
}
func BenchmarkGargantuan3(b *testing.B) {
n := 10000000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex3(str, replacement, index)
}
}
func BenchmarkGargantuan4(b *testing.B) {
n := 10000000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex4(str, replacement, index)
}
}
func BenchmarkGargantuan5(b *testing.B) {
n := 10000000
str, index, replacement := generateString(n), n / 2, 'B'
b.ResetTimer()
for i := 0; i < b.N; i++ {
replaceAtIndex5(str, replacement, index)
}
}
func main(){}
结果：
BenchmarkSmall1-8 20000000 99.9 ns/op
BenchmarkSmall2-8 50000000 29.5 ns/op
BenchmarkSmall3-8 20000000 58.1 ns/op
BenchmarkSmall4-8 50000000 32.0 ns/op
BenchmarkSmall5-8 1000000000 2.93 ns/op
BenchmarkMedium1-8 1000000 1034 ns/op
BenchmarkMedium2-8 20000000 68.4 ns/op
BenchmarkMedium3-8 20000000 78.8 ns/op
BenchmarkMedium4-8 30000000 49.3 ns/op
BenchmarkMedium5-8 1000000000 3.02 ns/op
BenchmarkBig1-8 20000 89557 ns/op
BenchmarkBig2-8 1000000 1204 ns/op
BenchmarkBig3-8 1000000 1257 ns/op
BenchmarkBig4-8 1000000 1200 ns/op
BenchmarkBig5-8 1000000000 2.93 ns/op
BenchmarkHuge2-8 200000 10260 ns/op
BenchmarkHuge3-8 200000 9908 ns/op
BenchmarkHuge4-8 100000 13628 ns/op
BenchmarkHuge5-8 1000000000 2.99 ns/op
BenchmarkGargantuan2-8 2000 822881 ns/op
BenchmarkGargantuan3-8 2000 807522 ns/op
BenchmarkGargantuan4-8 1000 2148387 ns/op
BenchmarkGargantuan5-8 1000000000 2.96 ns/op