Go如何做字符串比较? [英] How does Go do string comparison?
问题描述
http://golang.org/ref/spec#Comparison_operators
Go支持没有任何特殊功能的字符串比较。 Go运行时是否在后台工作以比较字符串文字?
Go supports string comparison without any special functions. Does the Go runtime do work behind the scenes to make comparisons of string literals?
推荐答案
正如您在下面的程序集转储中看到的,字符串比较在短路检查后委托给运行时(第17行)的 runtime.eqstring
函数,以查看两个操作数是否是相同的内存字符串第11行):
As you can see in the following assembly dump, string comparison is delegated to a runtime.eqstring
function from the runtime (line 17) after a short circuit check to see if the two operands are the same in-memory string (line 11):
$ cat foo.go
package main
func main() {
a := "hello"
b := "world"
_ = a == b
}
$ go tool 6g -S foo.go
--- prog list "main" ---
0000 (foo.go:3) TEXT main+0(SB),$40-0
0001 (foo.go:3) LOCALS ,$0
0002 (foo.go:4) LEAQ go.string."hello"+0(SB),BX
0003 (foo.go:4) MOVQ (BX),SI
0004 (foo.go:4) MOVQ 8(BX),CX
0005 (foo.go:5) LEAQ go.string."world"+0(SB),BX
0006 (foo.go:5) MOVQ (BX),DX
0007 (foo.go:5) MOVQ 8(BX),AX
0008 (foo.go:6) JMP ,11
0009 (foo.go:6) MOVQ $1,AX
0010 (foo.go:6) JMP ,23
0011 (foo.go:6) CMPQ CX,AX
0012 (foo.go:6) JNE ,22
0013 (foo.go:6) MOVQ SI,(SP)
0014 (foo.go:6) MOVQ CX,8(SP)
0015 (foo.go:6) MOVQ DX,16(SP)
0016 (foo.go:6) MOVQ AX,24(SP)
0017 (foo.go:6) CALL ,runtime.eqstring+0(SB)
0018 (foo.go:6) MOVBQZX 32(SP),BX
0019 (foo.go:6) CMPB BX,$0
0020 (foo.go:6) JEQ ,22
0021 (foo.go:6) JMP ,9
0022 (foo.go:6) MOVQ $0,AX
0023 (foo.go:7) RET ,
--- prog list "init" ---
0024 (foo.go:7) TEXT init+0(SB),$0-0
0025 (foo.go:7) MOVBQZX initdone·+0(SB),AX
0026 (foo.go:7) LOCALS ,$0
0027 (foo.go:7) CMPB AX,$0
0028 (foo.go:7) JEQ ,34
0029 (foo.go:7) CMPB AX,$2
0030 (foo.go:7) JNE ,32
0031 (foo.go:7) RET ,
0032 (foo.go:7) CALL ,runtime.throwinit+0(SB)
0033 (foo.go:7) UNDEF ,
0034 (foo.go:7) MOVB $2,initdone·+0(SB)
0035 (foo.go:7) RET ,
除非您正在编译器或运行时,这不应该过多地关注你:只需使用规范定义的运算符,并期望与字符串长度的比较为O(n)。
Unless you are working on the compiler or runtime, this shouldn't concern you too much: just use the operators as the spec defines, and expect that the comparison to be O(n) with the length of the string.
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