I am creating a phonebook program that can read VCards. The problem is with phone numbers. Normally, they will be like this in the United States:
0771234560
But if the phone number is from a foreign country, it would look like this.
+94771234560 or maybe (22)772324000
Now there are + and () signs to deal with! I am currently converting phone numbers (VCards contain them as Strings) to numbers. However, if I take allow phone numbers as strings, then a user could do something crazy, like insert a name as a phone number in the contact form.
How can I store phone numbers as strings but prevent problematic entries?
Definitely use a string, but validate it. Just because it's a string doesn't mean you have to accept any data. You should consider using a regular expression (or perhaps a series of regular expressions) to validate the data.
Don't just limit it to specific characters - for example, you don't want to accept ")0(" as a phone number - use sensible patterns. The Wikipedia page on local conventions for phone numbers may prove helpful on this front - or you could look for other sources. You may also want to consider being somewhat lenient, as not everyone will follow exact patterns. There's a delicate balance to be achieved though.
Don't use a numeric type for phone numbers, stick with a String.
Do some form of input validation. Define some restrictions on your phone numbers, and when reading the card, check the String against your format: if the phone number doesn't match your restrictions, then reject it.
Search around this site for questions/answers regarding phone number validation.
What would adding two phone numbers mean? So, IMO, not a number.
You should still attempt to validate, but if you want to accept any and all arbitrary international numbers, including local conventions for how they're written, that'll be frustrating.
来源：https://stackoverflow.com/questions/12331656/how-can-i-prevent-bad-inputs-when-storing-phone-numbers-as-strings