PHP date and time processing functions in detail

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Working with dates and times is a common task in web development, and PHP provides a number of powerful date and time handling functions such as strtotime, date and DateTimeImmutable::createFromFormat.

These functions make it easy to convert between different time formats, perform date and time calculations, and format output.

In this article, we’ll take a closer look at the usage and advantages of these three functions.

1. strtotime function

The strtotime function is used to convert human-readable date and time strings to Unix timestamps. It takes a datetime string as an argument and tries to parse it and convert it to a corresponding Unix timestamp. In addition to accepting the basic datetime format, it also understands various relative time expressions. Here are the arguments and roles of the strtotime function.

strtotime(string $datetime, ?int $baseTimestamp = null): int|false
  • Parameters: string $datetime, ?int $baseTimestamp = null.
  • $datetime: datetime string to be parsed.
  • $baseTimestamp: optional, indicates the base timestamp used to calculate the relative date.
  • Return value: the corresponding Unix timestamp is returned if parsing succeeds, or false if parsing fails.

When using the strtotime function, you can pass in a variety of datetime strings in different formats, including absolute times (e.g. “2023-08-06”, “15:30:00”) and relative times (e.g. “tomorrow”, “next week”).

The function will try to make a reasonable date-time conversion based on the incoming string, which is convenient for time calculations and comparisons.

echo strtotime("2023-08-06 15:30:00"), PHP_EOL;
echo strtotime("tomorrow"), PHP_EOL;
echo strtotime("+1 day"), PHP_EOL;

2. date Function

The date function is used to format a Unix timestamp into a desired date and time string. It takes a format string and a Unix timestamp as arguments and returns a formatted date-time string. The following are the arguments to the date function and what it does.

date(string $format, ?int $timestamp = null): string
  • Parameters: string $format, ?int $timestamp = null.
  • $format: datetime format string containing various formatting options to define the datetime style of the output.
  • $timestamp: optional parameter indicating the Unix timestamp to be formatted. Defaults to the return value of the time() function, which is the current Unix timestamp.
  • Return Value: Returns a formatted datetime string according to the specified format.

The first argument to the date function is a date format string containing various formatting options, such as “Y” for year, “m” for month, “d” for day, “H” for hour, “i” for minute, “s” for second, and so on.

// set the default timezone to use.
date_default_timezone_set('UTC');

// Prints something like: Monday
echo date("l");

// Prints something like: Monday 8th of August 2005 03:12:46 PM
echo date('l jS \of F Y h:i:s A');

// Prints: July 1, 2000 is on a Saturday
echo "July 1, 2000 is on a " . date("l", mktime(0, 0, 0, 7, 1, 2000));

/* use the constants in the format parameter */
// prints something like: Wed, 25 Sep 2013 15:28:57 -0700
echo date(DATE_RFC2822);

// prints something like: 2000-07-01T00:00:00+00:00
echo date(DATE_ATOM, mktime(0, 0, 0, 7, 1, 2000));

By combining these options, a variety of different date and time formats can be created.

3. DateTimeImmutable::createFromFormat function

The DateTimeImmutable::createFromFormat method is object-oriented date and time processing that parses a date string into a DateTimeImmutable object based on the specified format.

This is useful for dealing with different regional date formats or date strings that require more precise parsing.

public static DateTimeImmutable::createFromFormat(string $format, string $datetime, ?DateTimeZone $timezone = null): DateTimeImmutable|false

date_create_immutable_from_format(string $format, string $datetime, ?DateTimeZone $timezone = null): DateTimeImmutable|false

The following are the parameters and roles of the DateTimeImmutable::createFromFormat method:

  • Parameters: string $format, string $datetime, ?DateTimeZone $timezone = null
  • $format: datetime format string, used to specify the format of the input datetime string.
  • $datetime: datetime string to be parsed.
  • $timezone: optional parameter, used to set the timezone of the parsed DateTimeImmutable object. If not specified, the default is null, which means use the server’s timezone setting.
  • return value: return a DateTimeImmutable object if the parsing succeeds, or false if the parsing fails.

When using the DateTimeImmutable::createFromFormat method, you need to define a format string that matches the input datetime string.

$dateString = "06/08/2023";
$format = "d/m/Y";
$dateTime = DateTimeImmutable::createFromFormat($format, $dateString);

if ($dateTime instanceof DateTimeImmutable) {
    echo $dateTime->format("Y-m-d"); // 2023-08-06
}

4. Summary

Date and time handling is a common but complex task in PHP. The strtotime, date and DateTimeImmutable::createFromFormat functions provide us with powerful tools that make it easier to work with dates and times in different formats.

strtotime is used to convert strings to Unix timestamps, date is used to format timestamps into readable strings, and DateTimeImmutable::createFromFormat allows for more precise parsing of date strings.

By becoming proficient with these functions, you will be able to better handle and manage date-time related tasks and increase the efficiency of your web development.