Converting Dates to Timestamps in PHP

Timestamps are a common way to represent points in time numerically, and PHP provides several ways to convert human-readable dates into these timestamps. This tutorial explores the most reliable and flexible methods for date-to-timestamp conversion, focusing on best practices for accuracy and maintainability.

What is a Timestamp?

A timestamp represents the number of seconds that have elapsed since the Unix epoch (January 1, 1970, 00:00:00 Coordinated Universal Time (UTC)). This numerical representation makes it easy to compare and perform calculations on different points in time.

Using `strtotime()`

The simplest way to convert a date string to a timestamp is using the strtotime() function.

<?php
$date_string = '22-09-2008';
$timestamp = strtotime($date_string);

if ($timestamp === false) {
    echo "Invalid date format";
} else {
    echo $timestamp; // Output: 1221747200
}
?>

strtotime() is convenient, but it relies on interpreting the date string, which can lead to unexpected results if the input format is ambiguous. For example, strtotime('08-09-2008') might be misinterpreted as August 9th instead of September 8th, depending on your locale and PHP version. Therefore, explicit format specification is generally preferred.

Using the `DateTime` Class

The DateTime class provides a more robust and flexible way to work with dates and timestamps.

<?php
$date_string = '22-09-2008';

try {
    $dateTime = new DateTime($date_string);
    $timestamp = $dateTime->getTimestamp();
    echo $timestamp; // Output: 1221747200
} catch (Exception $e) {
    echo "Invalid date format: " . $e->getMessage();
}
?>

This approach is better because it throws an exception if the date string is invalid, allowing you to handle errors gracefully. However, like strtotime(), the constructor can still attempt to guess the format.

Explicit Format Specification with `DateTime::createFromFormat()`

To ensure accurate parsing, it’s crucial to explicitly specify the expected date format using DateTime::createFromFormat().

<?php
$date_string = '22-09-2008';
$format = '!d-m-Y'; // The exclamation mark suppresses time information

try {
    $dateTime = DateTime::createFromFormat($format, $date_string);

    if ($dateTime === false) {
        echo "Invalid date format";
    } else {
        $timestamp = $dateTime->getTimestamp();
        echo $timestamp; // Output: 1221747200
    }

} catch (Exception $e) {
    echo "Error parsing date: " . $e->getMessage();
}
?>

Here’s a breakdown of the format string:

d: Day of the month, two digits (01-31)
m: Month, two digits (01-12)
Y: Year, four digits (e.g., 2008)
!: This character is important! It tells createFromFormat to only parse the date part of the string and ignore any time information, effectively setting the time to midnight (00:00:00).

Handling Timezones

When working with dates and times, it’s often essential to consider timezones. The DateTime class allows you to specify a timezone during date creation or modify it later.

<?php
$date_string = '22-09-2008 00:00:00';
$format = 'd-m-Y H:i:s';

try {
    // Create a DateTime object with a specific timezone (e.g., EST)
    $dateTime = DateTime::createFromFormat($format, $date_string, new DateTimeZone('EST'));

    if ($dateTime === false) {
        echo "Invalid date format";
    } else {
        $timestamp = $dateTime->getTimestamp();
        echo $timestamp; // Output will vary based on EST offset
    }

} catch (Exception $e) {
    echo "Error parsing date: " . $e->getMessage();
}
?>

You can use other timezones like 'UTC' or 'America/New_York'. Using timezones ensures that your timestamps are consistent and accurate, regardless of the server’s location.

Best Practices

Always specify the date format: Use DateTime::createFromFormat() with an explicit format string to avoid ambiguity and potential errors.
Handle exceptions: Use try...catch blocks to gracefully handle invalid date strings and prevent your application from crashing.
Consider timezones: Specify the appropriate timezone when creating or modifying DateTime objects to ensure accuracy and consistency.
Validate Input: Before parsing the date string, consider validating the input to ensure it conforms to the expected format.