golang cannot parse json

Golang is a very practical programming language. Its main design goal is to improve the readability, maintainability and reliability of the program. When writing Golang programs, we often need to use JSON as the standard format for data serialization and communication. However, when using Golang to parse JSON, you sometimes encounter some problems, such as being unable to parse JSON. This article will introduce some common JSON parsing errors and provide some solutions.

1. Cannot parse empty JSON object

In Golang, we can use the json.Unmarsha1l function to parse JSON data into a structure or slice in the Go language. However, if we try to parse an empty JSON object, the Go language will report an error:

json: cannot unmarshal object into Go struct field .Field of type string

This is because the empty JSON object does not have any key-value pairs, so the parser cannot parse it into a Go structure. . The solution can be to use pointers to mark the structure fields as optional, so that empty JSON objects can be supported. For example:

type MyStruct struct {
    Field *string
}

data := []byte(`{}`)
var s MyStruct
err := json.Unmarshal(data, &s)
if err != nil {
    log.Fatal(err)
}
fmt.Println(s.Field) // output: <nil>

2. Cannot parse the null value in JSON

In JSON, null represents an empty value, and the corresponding type in Golang is nil. If we try to parse the null value in JSON, the Go language will report an error:

json: cannot unmarshal null into Go struct field .Field of type string

This is because the null value in JSON cannot be converted to a non-pointer type in the Go language. The solution is to use pointer types to declare structure fields:

type MyStruct struct {
    Field *string
}

data := []byte(`{"Field": null}`)
var s MyStruct
err := json.Unmarshal(data, &s)
if err != nil {
    log.Fatal(err)
}
fmt.Println(s.Field) // output: <nil>

3. Unable to parse empty arrays in JSON

In JSON, an empty array represents an array with no elements , the corresponding type in Golang is []. If we try to parse an empty array in JSON, the Go language will report an error:

json: cannot unmarshal array into Go struct field .Field of type []string

This is because the empty array cannot be converted to a slice of non-pointer type. The solution is to use pointer types to declare slices:

type MyStruct struct {
    Field *[]string
}

data := []byte(`{"Field": []}`)
var s MyStruct
err := json.Unmarshal(data, &s)
if err != nil {
    log.Fatal(err)
}
fmt.Println(s.Field) // output: &[]

4. Unable to parse nested objects in JSON

In JSON, we can nest multiple objects . However, when parsing nested objects, Golang will report an error:

json: cannot unmarshal object into Go struct field .Field of type string

This is because Golang cannot convert nested objects into non-structural type fields. The solution is to use structure types to parse nested objects:

type Field struct {
    Name string
}
type MyStruct struct {
    Field Field
}

data := []byte(`{"Field": {"Name": "value"}}`)
var s MyStruct
err := json.Unmarshal(data, &s)
if err != nil {
    log.Fatal(err)
}
fmt.Println(s.Field.Name) // output: "value"

5. Unable to parse non-ASCII characters in JSON

In JSON, we can use UTF-8 Character set to encode any character, including ASCII and non-ASCII characters. However, when parsing non-ASCII characters in JSON, Golang will report an error:

json: invalid character 'ò' looking for beginning of value

This is because the Go language uses UTF-8 encoding by default, and the characters in the JSON data may not be UTF-8 encoded. The solution is to use other encoding formats for parsing, such as the original binary encoding of JSON:

data := []byte{0x22, 0xC3, 0xB2, 0x22}
var s string
err := json.Unmarshal(data, &s)
if err != nil {
    log.Fatal(err)
}
fmt.Println(s) // output: "ò"

When writing Golang programs, we often need to use the JSON data format, but sometimes we encounter some problems when parsing JSON. . This article describes some common JSON parsing errors and provides some workarounds. Hopefully these tips will help you avoid some common mistakes when writing Golang programs.

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