C#•6mo ago

possible null reference warning

C#
static string? GetName()
        {
            string? input = default;
            bool needName = true;
            while (needName)
            {
                Console.WriteLine("What is your name?");
                input = Console.ReadLine();

                if (!input.All(char.IsLetterOrDigit) || String.IsNullOrEmpty(input)) //!!!
                {
                    Console.WriteLine("Please make sure that the name only contains letters or digits!");
                }
                else
                {
                    needName = false;
                }
            }
            return input;
        }

C#
static string? GetName()
        {
            string? input = default;
            bool needName = true;
            while (needName)
            {
                Console.WriteLine("What is your name?");
                input = Console.ReadLine();

                if (!input.All(char.IsLetterOrDigit) || String.IsNullOrEmpty(input)) //!!!
                {
                    Console.WriteLine("Please make sure that the name only contains letters or digits!");
                }
                else
                {
                    needName = false;
                }
            }
            return input;
        }

16 Replies

Pobiega•6mo ago

check the return type on Console.ReadLine

MathallOP•6mo ago

it returns a string?

Pobiega•6mo ago

correct: string? meaning a nullable string so it might be null and calling input.All on null would do what?

MathallOP•6mo ago

ah i see sorry if this is a dumb question, but is there any way to remove the warning

Pobiega•6mo ago

certainly ! input = Console.ReadLine()!; for specifically readline, this is fine, since the only time it returns null is... a very specific scenario

MathallOP•6mo ago

Thanks a ton

Pobiega•6mo ago

in most cases, using ! to silence a null warning is... problematic you are just hiding what can likely be an error also, this entire method can be greatly simplified, if you are interested?

Angius•6mo ago

Console.ReadLine() ?? "" would probably be more idiomatic than !

MathallOP•6mo ago

I simply put the ! directly after input on the if statement is there something major that I am missing?

Pobiega•6mo ago

static string GetName() // make it `string`,since we only return when its not null
{
    while (true)
    {
        Console.WriteLine("What is your name?");
        var input = Console.ReadLine();

        if (string.IsNullOrWhiteSpace(input))
        {
            Console.WriteLine("Please enter a valid name!");
            continue;
        }

        if (!input.All(char.IsLetterOrDigit))
        {
            Console.WriteLine("Please make sure that the name only contains letters or digits!");
            continue;
        }

        return input;
    }

static string GetName() // make it `string`,since we only return when its not null
{
    while (true)
    {
        Console.WriteLine("What is your name?");
        var input = Console.ReadLine();

        if (string.IsNullOrWhiteSpace(input))
        {
            Console.WriteLine("Please enter a valid name!");
            continue;
        }

        if (!input.All(char.IsLetterOrDigit))
        {
            Console.WriteLine("Please make sure that the name only contains letters or digits!");
            continue;
        }

        return input;
    }

this is how I would write this method if you dont care about giving two different error messages, you can combine them again I just prefer to split it like this but the removal of the needName and inlining the return inside the loop is... just easier

MathallOP•6mo ago

oh yeah, im pretty sure that I started this with the intention of having the input be an out string but since i changed from that this is much better

Pobiega•6mo ago

also, note how I didn't need to do any ! to remove the null warning since we check string.IsNullOrWhitespace 🙂

MathallOP•6mo ago

ah Thanks a ton, this is really helpful

Sonath•6mo ago

the warning disappears if you start your if statement with the null check first, because it assumes that if it's true the 2nd boolean statement doesn't have to be checked.

 if (string.IsNullOrEmpty(input) || !input.All(char.IsLetterOrDigit))

 if (string.IsNullOrEmpty(input) || !input.All(char.IsLetterOrDigit))

but in general Pobiega's response is better, because it provides more details on the user regarding what went wrong

qqdev•6mo ago

CTRL+Z, right? Sounds like it would be worth to check for null as you did in the final solution :blobthumbsup:

Pobiega•6mo ago

yeah ctrl+z or if the input is redirected, so its pretty rare. I agree that its better to actually check for the null (since you can effectively treat it as "no input")

Gaming

Programming

possible null reference warning