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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