如果value为0，则输入值将为空，否则为value

Problem: I have created a simple form, where there's an input field "num". After submission I want to show the value of num in the same input field, in other words want to retain the input in that field. If the value was set to 0 then I want to ignore that.

I can do it in several languages but I'm not sure about how to do it in Golang. My current template file has,

<input type="text" placeholder="foo" name="bar" value="{{if gt .N 0 }} {{.N}} {{end}} "/> 

Server file contains:

data := &listOfReport {
        R: r,
        I: i,
        N: n
}
listTmpl := template.Must(template.New("list_tmpl").Parse(string(report.Template["xxx.tmpl"])))
if err := listTmpl.Execute(w, data); err != nil {
    http.Error(w, fmt.Sprintf("Error rendering template %v", err), 500)
}

Another thought is to make N a string so make it '' or value in the server file. But that actually spoils the variable's name/purpose.

Is there any better way to do it? Is ther any better way to access GET parameters directly from template? Please note that the value of N is originally got from a GET variable.

*This code is not tested

There is no standard/builtin way to get any request parameters from within a template, you'll have to put it into your data. (You could write a function which does this for you, but that will result in an ugly hack.)

I don't see what's wrong with your solution.

I take a similar approach, but use structs.

type SignupForm struct {
    Name string
    Email string
    Etcera bool
}

// Type alias
type M map[string]interface{}

...

// In the handler that accepts your form
err := r.ParseForm()
if err != nil {
    // handle error
}

signup := SignupForm{}
err := decoder.Decode(signup, r.PostForm)
if err != nil {
    // handle error
}

// Store the 'saved' form contents somewhere temporary - 
// e.g.
//  - cookies (keep in mind the 4K browser limit)
//  - server side sessions (Redis; how I do it)
//  - db

// In the handler that renders your form
err := template.ExecuteTemplate(w, "form.html", M{
        "form": signup,
        "csrfToken": csrfToken,
        // and so on...
        })

Note that wherever you store the form data, make sure it is temporary. Server side sessions are ideal as you can have them expire (if you don't want to delete them manually).