Go字符串连接
对于字符串的连接大致有两种方式:
1、通过+号连接
func StrPlus1(a []string) string {
var s, sep string
for i := 0; i < len(a); i++ {
s += sep + a[i]
sep = " "
}
return s
}
2、通过strings.Join连接
func StrPlus2(a []string) string {
return strings.Join(a, " ")
}
对比两种方式的效率,通过压力测试进行对比
import "testing"
func BenchmarkStrPlus1(b *testing.B) {
for i := 0; i < b.N; i++ {
StrPlus1([]string{"xxx", "bbb", "aaa"})
}
}
func BenchmarkStrPlus2(b *testing.B) {
for i := 0; i < b.N; i++ {
StrPlus2([]string{"xxx", "bbb", "aaa"})
}
}
运行压力测试go test -test.bench=".*"
goos: darwin
goarch: amd64
BenchmarkStrPlus1-4 10000000 127 ns/op
BenchmarkStrPlus2-4 20000000 78.7 ns/op
从本机来看通过+号连接字符串每个操作消耗127ns时间,strings.Join消耗78.7ns。效率上strings.Join更高
来看下strings包中Join的实现
// Join concatenates the elements of a to create a single string. The separator string
// sep is placed between elements in the resulting string.
func Join(a []string, sep string) string {
switch len(a) {
case 0:
return ""
case 1:
return a[0]
case 2:
// Special case for common small values.
// Remove if golang.org/issue/6714 is fixed
return a[0] + sep + a[1]
case 3:
// Special case for common small values.
// Remove if golang.org/issue/6714 is fixed
return a[0] + sep + a[1] + sep + a[2]
}
n := len(sep) * (len(a) - 1)
for i := 0; i < len(a); i++ {
n += len(a[i])
}
b := make([]byte, n)
bp := copy(b, a[0])
for _, s := range a[1:] {
bp += copy(b[bp:], sep)
bp += copy(b[bp:], s)
}
return string(b)
}
可以看出当连接字符串数量较大时,是先通过make分配足够的空间,然后把每个字符串copy到空间里面,而不是每次通过+号来多次分配内存。