Golang time.Time.AppendFormat

The time.Time.AppendFormat method in Golang is part of the time package and is used to format a time.Time object according to a specified layout and append the result to a byte slice. This method is particularly useful when you want to efficiently build strings or byte slices with formatted dates and times without creating intermediate strings.

Table of Contents

1. Introduction
2. time.Time.AppendFormat Method Syntax
3. Examples
   • Basic Usage
   • Appending Formatted Date to a Byte Slice
   • Building a Custom Log Entry
4. Real-World Use Case
5. Conclusion

Introduction

The time.Time.AppendFormat method formats a time.Time object according to the provided layout and appends the formatted result to a byte slice. This method is efficient for scenarios where you need to concatenate formatted dates and times with other data into a single byte slice or string.

time.Time.AppendFormat Method Syntax

The syntax for the time.Time.AppendFormat method is as follows:

func (t Time) AppendFormat(b []byte, layout string) []byte

Parameters:

• b: A byte slice to which the formatted time will be appended.
• layout: A string representing the layout (format) to apply to the time.Time object.

Returns:

• []byte: A byte slice containing the original content of b followed by the formatted time.

Examples

Basic Usage

This example demonstrates how to use the time.Time.AppendFormat method to append a formatted time to a byte slice.

Example

package main

import (
	"fmt"
	"time"
)

func main() {
	// Define the current time
	currentTime := time.Now()

	// Define a byte slice to append to
	initialBytes := []byte("Current time: ")

	// Append the formatted time to the byte slice
	formattedBytes := currentTime.AppendFormat(initialBytes, "2006-01-02 15:04:05")

	// Convert the byte slice to a string and print it
	fmt.Println(string(formattedBytes))
}

Output:

Current time: 2024-08-08 12:00:00

Appending Formatted Date to a Byte Slice

This example shows how to append a formatted date to a byte slice and then further append additional text.

Example

package main

import (
	"fmt"
	"time"
)

func main() {
	// Define a specific date
	date := time.Date(2024, time.August, 8, 0, 0, 0, 0, time.UTC)

	// Start with an initial byte slice
	initialBytes := []byte("Date: ")

	// Append the formatted date to the byte slice
	formattedBytes := date.AppendFormat(initialBytes, "2006-01-02")

	// Append more text to the byte slice
	formattedBytes = append(formattedBytes, " - Important event"...)

	// Convert the byte slice to a string and print it
	fmt.Println(string(formattedBytes))
}

Output:

Date: 2024-08-08 - Important event

Building a Custom Log Entry

This example demonstrates how to build a custom log entry by appending a formatted timestamp to a byte slice, followed by a log message.

Example

package main

import (
	"fmt"
	"time"
)

func main() {
	// Define the current time
	currentTime := time.Now()

	// Start with an initial byte slice for the log entry
	logEntry := []byte("Log entry at ")

	// Append the formatted time to the log entry
	logEntry = currentTime.AppendFormat(logEntry, "2006-01-02 15:04:05")

	// Append the log message
	logEntry = append(logEntry, ": Application started"...)

	// Convert the byte slice to a string and print the log entry
	fmt.Println(string(logEntry))
}

Output:

Log entry at 2024-08-08 12:00:00: Application started

Real-World Use Case

Efficiently Building HTTP Headers

In real-world applications, the time.Time.AppendFormat method can be used to efficiently build HTTP headers that include timestamps. This method minimizes memory allocations by appending directly to an existing byte slice, which is particularly useful in performance-critical applications.

Example: Building a Date Header for an HTTP Request

package main

import (
	"fmt"
	"time"
)

func main() {
	// Define the current time
	currentTime := time.Now()

	// Start with an initial byte slice for the HTTP header
	header := []byte("Date: ")

	// Append the formatted date to the header in RFC1123 format
	header = currentTime.AppendFormat(header, time.RFC1123)

	// Print the header
	fmt.Println(string(header))
}

Output:

Date: Thu, 08 Aug 2024 12:00:00 UTC

Conclusion

The time.Time.AppendFormat method in Go is a powerful and efficient tool for formatting and appending time values to byte slices. It is particularly useful in performance-critical scenarios where minimizing memory allocations is important, such as in logging, building HTTP headers, or constructing complex strings with timestamps. Whether you are appending formatted dates to logs, messages, or headers, time.Time.AppendFormat provides a flexible and efficient way to handle time formatting in Go.