How to correctly encapsulate log.Printf and pass parameters in Go language?

Detailed explanation of custom packaging and parameter delivery of Go language log output

In Go language development, custom log output is often required, such as controlling log level or format. This article will explain in detail how to correctly encapsulate the log.Printf function and pass parameters to solve the problem of parameter passing errors.

Problem: The developer tried to encapsulate log.Printf , but the output result of the custom function did not match expectations, and an error message similar to " [jim %!s(int=18)],今年%!d(missing) " appeared. The original code is as follows:

 package main

import "log"

func main() {
    debugf("My name is %s, this year %d", "jim", 18)
}

func debugf(str string, arg ...interface{}) {
    if true {
        log.Printf(str "\n", arg) // Error: Parameter delivery method is incorrect}
}

Cause: log.Printf expects to receive a formatted string and multiple parameters of type interface{} that replace placeholders in the formatted string. The original code passes the entire arg slice as a single parameter to log.Printf instead of passing the slice elements one by one, causing log.Printf to not parse the placeholder correctly.

Solution: You need to expand the arg slice and pass each element as an independent parameter to log.Printf . The modified debugf function is as follows:

 func Debugf(str string, arg ...interface{}) {
    if true {
        log.Printf(str "\n", arg...) // Correct: Use... Expand parameters}
}

By adding ... after arg , we expand the elements in arg slice, passing them as independent parameters to log.Printf . In this way, log.Printf can correctly parse and replace placeholders and output correct log information, such as: " 2024-10-27 10:30:00 我叫jim,今年18 " (the timestamp may be slightly different). This emphasizes the importance of correctly expanding parameters for the correct use of log.Printf .

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