Standard Library Utilities

Bytes Buffer

A bytes.Buffer builds text step by step when a program needs to assemble a result.

buffer A buffer holds pieces of data while a program builds a final value.

Bytes Buffer

word
bytes_buffer.go
Replay: real traced execution (multi-file project)
package main

import (
	"bytes"
	"fmt"
)

func main() {
	var word = "alpha"
	var buffer bytes.Buffer
	buffer.WriteString("item:")
	buffer.WriteString(word)
	buffer.WriteString(":done")
	result := buffer.String()

	fmt.Println("word=", word)
	fmt.Println("result=", result)
	fmt.Println("length=", len(result))
}

package main

import (
	"bytes"
	"fmt"
)

func main() {
	var word = "beta"
	var buffer bytes.Buffer
	buffer.WriteString("item:")
	buffer.WriteString(word)
	buffer.WriteString(":done")
	result := buffer.String()

	fmt.Println("word=", word)
	fmt.Println("result=", result)
	fmt.Println("length=", len(result))
}

package main

import (
	"bytes"
	"fmt"
)

func main() {
	var word = "go"
	var buffer bytes.Buffer
	buffer.WriteString("item:")
	buffer.WriteString(word)
	buffer.WriteString(":done")
	result := buffer.String()

	fmt.Println("word=", word)
	fmt.Println("result=", result)
	fmt.Println("length=", len(result))
}

  1. word ← "alpha", buffer ← bytes.Buffer{buf:[]uint8(nil), off:0, lastRead:0}

    8func main() {9  var word→ "alpha" = "alpha" //@word="beta", "go"10  var buffer→ bytes.Buffer{buf:[]uint8(nil), off:0, lastRead:0} bytes.Buffer11  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a}, off:0, lastRead:0}.WriteString("item:")12  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x61, 0x6c, 0x70, 0x68, 0x61}, off:0, lastRead:0}.WriteString(word"alpha")13  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x61, 0x6c, 0x70, 0x68, 0x61, 0x3a, 0x64, 0x6f, 0x6e, 0x65}, off:0, lastRead:0}.WriteString(":done")14  result→ "item:alpha:done" := bufferbytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x61, 0x6c, 0x70, 0x68, 0x61, 0x3a, 0x64, 0x6f, 0x6e, 0x65}, off:0, lastRead:0}.String()1516  fmt.Println("word=", word"alpha")17  fmt.Println("result=", result"item:alpha:done")18  fmt.Println("length=", len(result"item:alpha:done"))19}
    outputword= alpha
result= item:alpha:done
length= 15

  1. word ← "beta", buffer ← bytes.Buffer{buf:[]uint8(nil), off:0, lastRead:0}

    8func main() {9  var word→ "beta" = "beta"10  var buffer→ bytes.Buffer{buf:[]uint8(nil), off:0, lastRead:0} bytes.Buffer11  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a}, off:0, lastRead:0}.WriteString("item:")12  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x62, 0x65, 0x74, 0x61}, off:0, lastRead:0}.WriteString(word"beta")13  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x62, 0x65, 0x74, 0x61, 0x3a, 0x64, 0x6f, 0x6e, 0x65}, off:0, lastRead:0}.WriteString(":done")14  result→ "item:beta:done" := bufferbytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x62, 0x65, 0x74, 0x61, 0x3a, 0x64, 0x6f, 0x6e, 0x65}, off:0, lastRead:0}.String()1516  fmt.Println("word=", word"beta")17  fmt.Println("result=", result"item:beta:done")18  fmt.Println("length=", len(result"item:beta:done"))19}
    outputword= beta
result= item:beta:done
length= 14

  1. word ← "go", buffer ← bytes.Buffer{buf:[]uint8(nil), off:0, lastRead:0}

    8func main() {9  var word→ "go" = "go"10  var buffer→ bytes.Buffer{buf:[]uint8(nil), off:0, lastRead:0} bytes.Buffer11  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a}, off:0, lastRead:0}.WriteString("item:")12  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x67, 0x6f}, off:0, lastRead:0}.WriteString(word"go")13  buffer→ bytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x67, 0x6f, 0x3a, 0x64, 0x6f, 0x6e, 0x65}, off:0, lastRead:0}.WriteString(":done")14  result→ "item:go:done" := bufferbytes.Buffer{buf:[]uint8{0x69, 0x74, 0x65, 0x6d, 0x3a, 0x67, 0x6f, 0x3a, 0x64, 0x6f, 0x6e, 0x65}, off:0, lastRead:0}.String()1516  fmt.Println("word=", word"go")17  fmt.Println("result=", result"item:go:done")18  fmt.Println("length=", len(result"item:go:done"))19}
    outputword= go
result= item:go:done
length= 12