How to Handle 'json: cannot unmarshal string into Go value of type float64' Errors When Decoding JSON?

Decoding JSON with Type Conversion from String to Float64

When decoding a JSON string containing a floating-point number, it's possible to encounter the error "json: cannot unmarshal string into Go value of type float64." This issue arises when the JSON decoder attempts to automatically convert the number from a string to a float64 type.

To solve this issue, you can explicitly tell the JSON decoder that the string represents a float64 by using the ",string" tag in the struct definition:

type Product struct {
    Name  string
    Price float64 `json:",string"`
}

By adding this tag, the JSON decoder will treat the "price" field as a string encoded float64, allowing for proper conversion during decoding.

package main

import (
    "encoding/json"
    "fmt"
)

type Product struct {
    Name  string
    Price float64 `json:",string"`
}

func main() {
    s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
    var pro Product
    err := json.Unmarshal([]byte(s), &pro)
    if err == nil {
        fmt.Printf("%+v\n", pro)
    } else {
        fmt.Println(err)
        fmt.Printf("%+v\n", pro)
    }
}

With this modification, the program will now successfully decode the JSON string and correctly convert the "price" field to a float64 type.

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