如何验证字符串仅包含某些字符

Question

I am working on an assignment for school:

I have passed a string to a mutator and I need to validate that it only contains spaces, hyphens or upper and lower case letters.

The output is always " ".

Can you see what I am doing wrong? Is there a smarter way to do this? I got this way from my instructor but its not working. Here is my code:

public void setFirstName(string newFirstName

{

    bool valid;

    valid = System.Text.RegularExpressions.Regex.IsMatch(newFirstName, "^[- a-zA-Z]?$");

    if (valid)

    {

        firstName = newFirstName;

    }

        firstName = " ";

}

Answer 1

You need else block.

public void setFirstName(string newFirstName)
{
    bool valid;
    valid = System.Text.RegularExpressions.Regex.IsMatch(newFirstName, "^[- a-zA-Z]*$");
    if (valid)
    {
        firstName = newFirstName;
    }
    else
    {
        firstName = " ";
    }
}

Update

Your regex seems also wrong it needs * for zero or more occurance instead of ?. Correct regex => ^[- a-zA-Z]*$

Click here to see working fiddle => link

Answer 2

As an alternative to RegEx (which I would not recommend if you're still just learning C#), you can use basic string validation with LINQ and the built in .Net char methods .

bool isValid = newFirstName.All(x => char.IsLetter(x) || x == '-' || x == ' ');

In this particular case, All will check that every element in the array (a string is a char array) matches the predicate provided where every character:

• must be a letter (upper or lower) OR
• must be a dash '-' OR
• must be a space ' '

If anyone of those conditions fail, then the result will be false.