如何在正则表达式中设置必填字符？手机号正则验证需求咨询

Hey there! Let's get that phone number validation sorted out for you. Your current regex has two key issues that are keeping it from meeting your requirements:

• It doesn't enforce the leading + sign as a mandatory character
• The trailing + in your pattern is unnecessary (it’s actually a regex quantifier modifier here, which isn’t what you want)

The Correct Regex #

To validate a 13-character phone number that must start with + followed by 12 digits, use this pattern:

/^\+\d{12}$/

Let's break it down clearly:

• ^ : Anchors the match to the start of the string (ensures nothing comes before the +)
• \+ : Matches the literal + sign (we escape it with a backslash because + is a special character in regex)
• \d{12} : Matches exactly 12 digits (since the + takes up 1 character, this brings the total length to 13)
• $ : Anchors the match to the end of the string (ensures no extra characters are added after the digits)

Updated Validation Function #

Here's your revised function using the correct regex:

function validate_mobile($mobile) {
    return preg_match('/^\+\d{12}$/', $mobile);
}

Quick Test Cases #

• Valid number: +123456789001 → returns 1 (matches successfully)
• Invalid number (no leading +): 1234566780111 → returns 0 (fails)
• Invalid number (too short): +12345678900 → returns 0 (only 12 total characters)

内容的提问来源于stack exchange，提问作者silent_coder14