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https://github.com/ianlopshire/go-fixedwidth

Encoding and decoding for fixed-width formatted data
https://github.com/ianlopshire/go-fixedwidth

decoding encoding fixed-width

Last synced: 19 days ago
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Encoding and decoding for fixed-width formatted data

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README 

        
# fixedwidth [![GoDoc](https://godoc.org/github.com/ianlopshire/go-fixedwidth?status.svg)](http://godoc.org/github.com/ianlopshire/go-fixedwidth) [![Report card](https://goreportcard.com/badge/github.com/ianlopshire/go-fixedwidth)](https://goreportcard.com/report/github.com/ianlopshire/go-fixedwidth) [![Go Cover](http://gocover.io/_badge/github.com/ianlopshire/go-fixedwidth)](http://gocover.io/github.com/ianlopshire/go-fixedwidth)



Package fixedwidth provides encoding and decoding for fixed-width formatted Data.



`go get github.com/ianlopshire/go-fixedwidth`



## Usage



### Struct Tags



The struct tag schema schema used by fixedwidth is: `fixed:"{startPos},{endPos},[{alignment},[{padChar}]]"`[1](#f1).



The `startPos` and `endPos` arguments control the position within a line. `startPos` and `endPos` must both be positive integers greater than 0. Positions start at 1. The interval is inclusive. 



The `alignment` argument controls the alignment of the value within it's interval. The valid options are `default`[2](#f2), `right`, and `left`. The `alignment` is optional and can be omitted.



The `padChar` argument controls the character that will be used to pad any empty characters in the interval after writing the value. The default padding character is a space. The `padChar` is optional and can be omitted.



Fields without tags are ignored.



### Encode

```go

// define some data to encode

people := []struct {

    ID        int     `fixed:"1,5"`

    FirstName string  `fixed:"6,15"`

    LastName  string  `fixed:"16,25"`

    Grade     float64 `fixed:"26,30"`

    Age       uint    `fixed:"31,33"`

    Alive     bool    `fixed:"34,39"`

}{

    {1, "Ian", "Lopshire", 99.5, 20, true},

}



data, err := Marshal(people)

if err != nil {

    log.Fatal(err)

}

fmt.Printf("%s", data)

// Output:

// 1    Ian       Lopshire  99.5020 true

```



### Decode

```go

// define the format

var people []struct {

    ID        int     `fixed:"1,5"`

    FirstName string  `fixed:"6,15"`

    LastName  string  `fixed:"16,25"`

    Grade     float64 `fixed:"26,30"`

    Age       uint    `fixed:"31,33"`

    Alive     bool    `fixed:"34,39"`

    Github    bool    `fixed:"40,41"`

}



// define some fixed-with data to parse

data := []byte("" +

    "1    Ian       Lopshire  99.50 20 false f" + "\n" +

    "2    John      Doe       89.50 21 true t" + "\n" +

    "3    Jane      Doe       79.50 22 false F" + "\n" +

    "4    Ann       Carraway  79.59 23 false T" + "\n")



err := Unmarshal(data, &people)

if err != nil {

    log.Fatal(err)

}



fmt.Printf("%+v\n", people[0])

fmt.Printf("%+v\n", people[1])

fmt.Printf("%+v\n", people[2])

fmt.Printf("%+v\n", people[3])

// Output:

//{ID:1 FirstName:Ian LastName:Lopshire Grade:99.5 Age:20 Alive:false Github:false}

//{ID:2 FirstName:John LastName:Doe Grade:89.5 Age:21 Alive:true Github:true}

//{ID:3 FirstName:Jane LastName:Doe Grade:79.5 Age:22 Alive:false Github:false}

//{ID:4 FirstName:Ann LastName:Carraway Grade:79.59 Age:23 Alive:false Github:true}

```



It is also possible to read data incrementally



```go

decoder := fixedwidth.NewDecoder(bytes.NewReader(data))

for {

    var element myStruct

    err := decoder.Decode(&element)

    if err == io.EOF {

        break

    }

    if err != nil {

        log.Fatal(err)

    }

    handle(element)

}

```



### UTF-8, Codepoints, and Multibyte Characters



fixedwidth supports encoding and decoding fixed-width data where indices are expressed in

unicode codepoints and not raw bytes. The data must be UTF-8 encoded.



```go

decoder := fixedwidth.NewDecoder(strings.NewReader(data))

decoder.SetUseCodepointIndices(true)

// Decode as usual now

```



```go

buff := new(bytes.Buffer)

encoder := fixedwidth.NewEncoder(buff)

encoder.SetUseCodepointIndices(true)

// Encode as usual now

```



### Alignment Behavior



| Alignment | Encoding | Decoding |

| --------- | -------- | -------- |

| `default` | Field is left aligned | The padding character is trimmed from both right and left of value |

| `left` | Field is left aligned | The padding character is trimmed from right of value |

| `right` | Field is right aligned | The padding character is trimmed from left of value |



## Notes

1. `{}` indicates an argument. `[]` indicates and optional segment [^](#a1)

2. The `default` alignment is similar to `left` but has slightly different behavior required to maintain backwards compatibility [^](#a2) 



## Licence

MIT