Here is a solution to get the country based on an international phone number without using the Google library.
Let me explain first why it is so difficult to figure out the country. The country code of few countries is 1 digit, 2, 3 or 4 digits. That would be simple enough. But the country code 1 is not just used for US, but also for Canada and some smaller places:
1339 USA
1340 Virgin Islands (Caribbean Islands)
1341 USA
1342 not used
1343 Canada
Digits 2..4 decide, if it is US or Canada or ... There is no easy way to figure out the country, like the first xxx are Canada, the rest US.
For my code, I defined a class which holds information for ever digit:
public class DigitInfo {
public char Digit;
public Country? Country;
public DigitInfo?[]? Digits;
}
A first array holds the DigitInfos for the first digit in the number. The second digit is used as an index into DigitInfo.Digits. One travels down that Digits chain, until Digits is empty. If Country is defined (i.e. not null) that value gets returned, otherwise any Country defined earlier gets returned:
country code 1: byPhone[1].Country is US
country code 1236: byPhone[1].Digits[2].Digits[3].Digits[6].Country is Canada
country code 1235: byPhone[1].Digits[2].Digits[3].Digits[5].Country is null. Since
byPhone[1].Country is US, also 1235 is US, because no other
country was found in the later digits
Here is the method which returns the country based on the phone number:
/// <summary>
/// Returns the Country based on an international dialing code.
/// </summary>
public static Country? GetCountry(ReadOnlySpan<char> phoneNumber) {
if (phoneNumber.Length==0) return null;
var isFirstDigit = true;
DigitInfo? digitInfo = null;
Country? country = null;
foreach (var digitChar in phoneNumber) {
var digitIndex = digitChar - '0';
if (isFirstDigit) {
isFirstDigit = false;
digitInfo = ByPhone[digitIndex];
} else {
if (digitInfo!.Digits is null) return country;
digitInfo = digitInfo.Digits[digitIndex];
}
if (digitInfo is null) return country;
country = digitInfo.Country??country;
}
return country;
}
The rest of the code (digitInfos for every country of the world, test code, ...) is too big to be posted here, but it can be found on Github:
https://github.com/PeterHuberSg/WpfWindowsLib/blob/master/WpfWindowsHelperLib/CountryCode.cs
The code is part of a WPF TextBox and the library contains also other controls for email addresses, etc. A more detailed description is on CodeProject: International Phone Number Validation Explained in Detail
Change 23.1.23: I moved CountryCode.cs to WpfWindowsHelperLib, which doesn't have any WPF dependencies, despite it's name.
