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Programming language: Go

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README

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

go get github.com/ianlopshire/go-fixedwidth

Usage

Struct Tags

Position within a line is controlled via struct tags. The tags should be formatted as fixed:"{startPos},{endPos}" where startPos and endPos are both positive integers greater than 0. Positions start at 1. The interval is inclusive. Fields without tags are ignored.

Encode

// 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"`
}{
    {1, "Ian", "Lopshire", 99.5},
}

data, err := fixedwidth.Marshal(people)
if err != nil {
    log.Fatal(err)
}
fmt.Printf("%s", data)
// Output:
// 1    Ian       Lopshire  99.50

Decode

// 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"`
}

// define some fixed-with data to parse
data := []byte("" +
    "1    Ian       Lopshire  99.50" + "\n" +
    "2    John      Doe       89.50" + "\n" +
    "3    Jane      Doe       79.50" + "\n")


err := fixedwidth.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])
// Output:
//{ID:1 FirstName:Ian LastName:Lopshire Grade:99.5}
//{ID:2 FirstName:John LastName:Doe Grade:89.5}
//{ID:3 FirstName:Jane LastName:Doe Grade:79.5}

It is also possible to read data incrementally

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)
}

If you have an input where the indices are expressed in unicode codepoints, and not raw bytes fixedwidth supports this. Your data must be UTF-8 encoded:

decoder := fixedwidth.NewDecoder(strings.NewReader(data))
decoder.SetUseCodepointIndices(true)
// Decode as usual now

Licence

MIT