PHP regular expression method to verify specific week number

Regular expression in PHP language is a powerful tool that can be used to match, search and replace text in strings. In web development, regular expressions are widely used to validate form data entered by users. This article will introduce how to use PHP regular expressions to verify a specific week number.

First of all, we need to understand how week numbers are expressed. In the case of 52 weeks in a year, there are two ways to express week numbers: ISO 8601 and North American way. ISO 8601 is a standard specification issued by the International Organization for Standardization (ISO). The format is YYYY-Www, where YYYY represents the year, W represents the week, and ww represents the week number, and the value range is 01 to 52. For example, the first week of 2019 is represented as 2019-W01. The North American method divides the year into four quarters, each quarter has 13 weeks, with the first week represented as 1 and the last week represented as 13. Therefore, the first week of 2019 is represented as 2019-01 and the last week is represented as 2019-52.

Next, we will introduce the methods of using regular expressions to verify ISO 8601 and North American methods respectively. The first is ISO 8601.

1. Verify the week number in ISO 8601 format

The week number in ISO 8601 format can be verified with the following regular expression:

$regex = '/^20d{2}-W([1-9]|[1-4][0-9]|5[0-2])$/';

This regular expression The formula verifies a four-digit year prefixed by 20, followed by -W and a week number from 1 to 52. Among them, [1-9] represents a single digit, 1-4 represents a number from 1 to 4 in the tens digit, a number from 0 to 9 in the ones digit, 5[0-2] represents a number in the fifty digit, and a number in the ones digit. Numbers from 0 to 2.

The following is a code example, using the preg_match() function for verification:

$week = '2019-W10';
if (preg_match('/^20d{2}-W([1-9]|[1-4][0-9]|5[0-2])$/', $week)) {
    echo $week . ' is a valid week number.';
} else {
    echo $week . ' is not a valid week number.';
}

//输出结果：2019-W10 is a valid week number.

In this example, we use the preg_match() function and pass in the regular expression in the first parameter, The second parameter is the string to be verified. If the return result is true, it means that the string conforms to the rules of the regular expression. If the return result is false, it means that the string does not comply with the rules.

2. Verify the week number in North American way

The week number in North American way can be verified with the following regular expression:

$regex = '/^20d{2}-(0[1-9]|1[0-3])$/';

This regular expression can Validates a four-digit year prefixed by 20, followed by a crossbar and a number from 01 to 13. Among them, 0[1-9] means that the tens digit is 0 and the ones digit is a number from 1 to 9; 1[0-3] means that the tens digit is 1 and the ones digit is a number from 0 to 3.

The following is a code example, also using the preg_match() function for verification:

$week = '2019-10';
if (preg_match('/^20d{2}-(0[1-9]|1[0-3])$/', $week)) {
    echo $week . ' is a valid week number.';
} else {
    echo $week . ' is not a valid week number.';
}

//输出结果：2019-10 is a valid week number.

Similar to the verification method of the ISO 8601 format, we can also use the preg_match() function for verification. The above two examples are to verify a specific number of weeks. If you need to verify the number of weeks within a period of time, you need to modify the regular expression rules. To verify all week numbers in 2019, the expression in ISO 8601 format should be /^2019-W([1-9]|1-4|5[0-2])$/, the North American expression Should be /^2019-(0[1-9]|1[0-3])$/.

To sum up, the method of using PHP regular expressions to verify a specific week number can be divided into ISO 8601 and North American methods. Through regular expression verification, the accuracy of form data can be ensured, thereby improving the stability and user experience of web applications.

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