Check if char isletter without special characters like á

Question

i want to check if a string only contains correct letters. I used Char.IsLetter for this. My problem is, when there are chars like é or á they are also said to be correct letters, which shouldn't be.

is there a possibility to check a char as a correct letter A-Z or a-z without special-letters like á?

Answer 1

bool IsEnglishLetter(char c)
{
    return (c>='A' && c<='Z') || (c>='a' && c<='z');
}

You can make this an extension method:

static bool IsEnglishLetter(this char c) ...

Answer 2

You can use Char.IsLetter(c) && c < 128 . Or just c < 128 by itself, that seems to match your problem the closest.

But you are solving an Encoding issue by filtering chars. Do investigate what that other application understands exactly.

It could be that you should just be writing with Encoding.GetEncoding(someCodePage).

Answer 3

You can use regular expression \w or [a-zA-Z] for it

Answer 4

Update in .NET 7

There is now a Char.IsAsciiLetter function which would exactly meet the requirements

Answer 5

In C# 9.0 you can use pattern matching enhancements.

public static bool IsLetter(this char c) =>
    c is >= 'a' and <= 'z' or >= 'A' and <= 'Z';

Answer 6

// Create the regular expression
string pattern = @"^[a-zA-Z]+$";
Regex regex = new Regex(pattern);

// Compare a string against the regular expression
return regex.IsMatch(stringToTest);

Answer 7

Use Linq for easy access:

if (yourString.All(char.IsLetter))
{
    //just letters are accepted.
}