How to Handle Unexpected Fields in fmt.Sprintf?

Handling Unexpected Fields in fmt.Sprintf

In Go programming, the fmt.Sprintf function is utilized to format strings. However, an issue arises when the input string contains unexpected fields, leading to a panic.

Problem

Let's consider the following code snippet:

<code class="go">package main

import "fmt"

func main() {
    tmp_str := "hello %s"
    str := fmt.Sprintf(tmp_str, "world")
    fmt.Println(str)
}</code>

In this example, tmp_str is a template string expecting a single argument. However, if the program receives a complete string like "Hello Friends" (instead of a template), fmt.Sprintf will panic due to the presence of an extra argument. The error message would be:

Hello Friends%!(EXTRA string=world)

Solution

One approach to handle this issue is to enforce the use of a valid %s verb in the template string. Users can provide a placeholder verb, such as %.0s or %.s, to indicate that the argument will be truncated to zero length if no matching field exists. Here's an example:

<code class="go">tmp_str := "Hello Friends%.s"</code>

Using %.s will truncate any extra fields, resulting in the desired output:

Hello Friends

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