You are reporting all the allocations made in a BenchmarkFmt function which
includes allocations made in the fmt.Println function. See
https://golang.org/src/fmt/print.go.
Peter
On Thursday, October 6, 2016 at 12:01:16 AM UTC-4, 刘桂祥 wrote:
>
>
>
> package main
>
>
> import (
> "fmt"
> _ "net/http/pprof"
> "testing"
> )
>
>
> // 8 Bytes/op 1 allocs/op
> func BenchmarkFmt1(b *testing.B) {
> b.ReportAllocs()
> for i := 0; i < b.N; i++ {
> fmt.Println(100)
> }
> }
>
>
> // 16 Bytes/op 1 allocs/op
> func BenchmarkFmt2(b *testing.B) {
> b.ReportAllocs()
> for i := 0; i < b.N; i++ {
> fmt.Println("hello")
> }
> }
>
>
> // 32 Bytes/op 1 allocs/op
> func BenchmarkFmt3(b *testing.B) {
> b.ReportAllocs()
> for i := 0; i < b.N; i++ {
> fmt.Println([]int{})
>
>
> }
> }
>
>
> // 48 Bytes/op 3 allocs/op
> func BenchmarkFmt4(b *testing.B) {
> b.ReportAllocs()
> for i := 0; i < b.N; i++ {
> fmt.Println([]int{100})
> }
> }
>
>
> // 64 Bytes/op 4 allocs/op
> func BenchmarkFmt5(b *testing.B) {
> b.ReportAllocs()
> for i := 0; i < b.N; i++ {
> fmt.Println([]int{100, 200})
> }
> }
>
> go version 1.7
>
> Fmt1 : the runtime alloc 100 in heap
> Fmt2: the runtime alloc a string header (addr len) in heap
> Fmt3: why the runtime alloc 32 bytes for slice header ??
> Fmt4: why have 3 allocs and 48 bytes ??
> Fmt5: why have 4 allocs and 64 bytes ??
>
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