go中实现字符切片和字符串互转
作者:~kiss~
这篇文章主要为大家详细介绍了go语言中如何实现字符切片和字符串互转,文中的示例代码讲解详细,具有一定的学习价值,感兴趣的小伙伴可以了解一下
Go 1.21
// 返回一个Slice,它的底层数组自ptr开始,长度和容量都是len func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType // 返回一个指针,指向底层的数组 func SliceData(slice []ArbitraryType) *ArbitraryType // 生成一个字符串,底层的数组开始自ptr,长度是len // returns a string value whose underlying bytes start at ptr and whose length is len // The len argument must be of integer type or an untyped constant // A constant len argument must be non-negative and representable by a value of type int // if it is an untyped constant it is given type int // At run time, if len is negative, or if ptr is nil and len is not zero, a run-time panic occurs // Since Go strings are immutable, the bytes passed to String must not be modified afterwards func String(ptr *byte, len IntegerType) string // 返回字符串底层的数组 // returns a pointer to the underlying bytes of str // For an empty string the return value is unspecified, and may be nil. // Since Go strings are immutable, the bytes returned by StringData must not be modified. func StringData(str string) *byte
Go 1.20
废弃两个类型SliceHeader和StringHeader
Go 1.19
string.SliceHeader和string.StringHeader经常用在 slice of byte 和 string 高效互转场景
// go1.18.3/src/reflect/value.go // SliceHeader is the runtime representation of a slice. // It cannot be used safely or portably and its representation may // change in a later release. // Moreover, the Data field is not sufficient to guarantee the data // it references will not be garbage collected, so programs must keep // a separate, correctly typed pointer to the underlying data. type SliceHeader struct { Data uintptr Len int Cap int } // StringHeader is the runtime representation of a string. // It cannot be used safely or portably and its representation may // change in a later release. // Moreover, the Data field is not sufficient to guarantee the data // it references will not be garbage collected, so programs must keep // a separate, correctly typed pointer to the underlying data. type StringHeader struct { Data uintptr Len int }
Slice比String多一个Cap字段
两个的数据都存储在Data数组中
实现方式
方式1
string(bytes)或[]byte(str)
性能不佳
方式2
// toBytes performs unholy acts to avoid allocations func toBytes(s string) []byte { return *(*[]byte)(unsafe.Pointer(&s)) } // toString performs unholy acts to avoid allocations func toString(b []byte) string { return *(*string)(unsafe.Pointer(&b)) }
方式3
func SliceByteToString(b []byte) string { return *(*string)(unsafe.Pointer(&b)) } func StringToSliceByte(s string) []byte { x := (*[2]uintptr)(unsafe.Pointer(&s)) h := [3]uintptr{x[0], x[1], x[1]} return *(*[]byte)(unsafe.Pointer(&h)) }
方式4
func Clone(s string) string { if len(s) == 0 { return "" } b := make([]byte, len(s)) copy(b, s) return *(*string)(unsafe.Pointer(&b)) }
性能测试
var L = 1024 * 1024 var str = strings.Repeat("a", L) var s = bytes.Repeat([]byte{'a'}, L) var str2 string var s2 []byte func BenchmarkString2Slice(b *testing.B) { for i := 0; i < b.N; i++ { bt := []byte(str) if len(bt) != L { b.Fatal() } } } func BenchmarkString2SliceReflect(b *testing.B) { for i := 0; i < b.N; i++ { bt := *(*[]byte)(unsafe.Pointer(&str)) if len(bt) != L { b.Fatal() } } } func BenchmarkString2SliceUnsafe(b *testing.B) { for i := 0; i < b.N; i++ { bt := unsafe.Slice(unsafe.StringData(str), len(str)) if len(bt) != L { b.Fatal() } } } func BenchmarkSlice2String(b *testing.B) { for i := 0; i < b.N; i++ { ss := string(s) if len(ss) != L { b.Fatal() } } } func BenchmarkSlice2StringReflect(b *testing.B) { for i := 0; i < b.N; i++ { ss := *(*string)(unsafe.Pointer(&s)) if len(ss) != L { b.Fatal() } } } func BenchmarkSlice2StringUnsafe(b *testing.B) { for i := 0; i < b.N; i++ { ss := unsafe.String(unsafe.SliceData(s), len(str)) if len(ss) != L { b.Fatal() } } }
官方出品必然是好东西,所以相信GO1.21即可
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