详解GO语言中[]byte与string的两种转换方式和底层实现

//[]byte转string
func b2s(b []byte) string {
    return *(*string)(unsafe.Pointer(&b))
}
 
//string转[]byte
func s2b(s string) (b []byte) {
    bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
    sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
    bh.Data = sh.Data
    bh.Cap = sh.Len
    bh.Len = sh.Len
    return b
}

// string is the set of all strings of 8-bit bytes, conventionally but not
// necessarily representing UTF-8-encoded text. A string may be empty, but
// not nil. Values of string type are immutable.

type string string

// string 转 []byte
s1 := "xiaoxu"
b := []byte(s1)

// []byte 转 string
s2 := string(b)

//[]byte转string
func b2s(b []byte) string {
    return *(*string)(unsafe.Pointer(&b))
}
 
//string转[]byte
func s2b(s string) (b []byte) {
    bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
    sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
    bh.Data = sh.Data
    bh.Cap = sh.Len
    bh.Len = sh.Len
    return b
}

const tmpStringBufSize = 32

//长度32的数组
type tmpBuf [tmpStringBufSize]byte

//时间函数
func stringtoslicebyte(buf *tmpBuf, s string) []byte {
    var b []byte
    //判断字符串长度是否小于等于32
    if buf != nil && len(s) <= len(buf) {
        *buf = tmpBuf{}
        b = buf[:len(s)]
    } else {
        //预定义数组长度不够，重新分配内存
        b = rawbyteslice(len(s))
    }
    copy(b, s)
    return b
}

// rawbyteslice allocates a new byte slice. The byte slice is not zeroed.
//rawbyteslice函数 分配一个新的字节片。字节片未归零
func rawbyteslice(size int) (b []byte) {
    cap := roundupsize(uintptr(size))
    p := mallocgc(cap, nil, false)
    if cap != uintptr(size) {
        memclrNoHeapPointers(add(p, uintptr(size)), cap-uintptr(size))
    }

    *(*slice)(unsafe.Pointer(&b)) = slice{p, size, int(cap)}
    return
}

const tmpStringBufSize = 32

//长度32的数组
type tmpBuf [tmpStringBufSize]byte

//实现函数
func slicebytetostring(buf *tmpBuf, ptr *byte, n int) (str string) {
    ...
    if n == 1 {
        p := unsafe.Pointer(&staticuint64s[*ptr])
        if goarch.BigEndian {
            p = add(p, 7)
        }
        stringStructOf(&str).str = p
        stringStructOf(&str).len = 1
        return
    }

    var p unsafe.Pointer
    //判断字符串长度是否小于等于32
    if buf != nil && n <= len(buf) {
        p = unsafe.Pointer(buf)
    } else {
        p = mallocgc(uintptr(n), nil, false)
    }
    stringStructOf(&str).str = p
    stringStructOf(&str).len = n
    //拷贝byte数组至字符串
    memmove(p, unsafe.Pointer(ptr), uintptr(n))
    return
}

//string转[]byte
func s2b(s string) (b []byte) {
    bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
    sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
    bh.Data = sh.Data
    bh.Cap = sh.Len
    bh.Len = sh.Len
    return b
}

//slice在运行时的描述符
type SliceHeader struct {      
     Data uintptr
     Len  int
    Cap  int
}

//string在运行时的描述符
type StringHeader struct {
    Data uintptr
    Len  int
}