int.TryParse = null if not numeric?

Question

is there some way of return null if it can\'t parse a string to int?

with:

public .... , string? categoryID) 
{
int.TryParse(categoryID, out categoryID);         


        

Answer 1

Here's a proper use of Int32.TryParse:

int? value;
int dummy;
if(Int32.TryParse(categoryID, out dummy)) {
    value = dummy;
}
else {
    value = null;
}
return value;

Answer 2

TryParse will return false if the string can't be parsed. You can use this fact to return either the parsed value, or null. Anyway I guess that you are intending to return int? from your method, then it would be something like this:

public int? ParseInt(string categoryID) 
{
    int theIntValue;
    bool parseOk = int.TryParse(categoryID, out theIntValue);
    if(parseOk) {
        return theIntValue;
    } else {
        return null;
    }
}

Answer 3

How about this?

public int? ParseToNull(string categoryId)
{
    int id;
    return int.TryParse(categoryId, out id) ? (int?)id : null;
}

Answer 4

Int is a value type which means there is no such thing as a null int. So no, TryParse will never alter the out parameter so that it is null.

But the problem you're having is you're passing a string to the out parameter of TryParse when its expecting an integer.

You need something like this...

Int categoryID = 0;
string strCategoryID = "somestringmaybeitsaninteger";

int.TryParse(strCategoryID, out categoryID);

Answer 5

** this answer was down-voted a lot ** Although it is a possible solution - it is a bad one performance wise, and probably not a good programming choice.

I will not delete it, as I guess many programmers might not be aware of this, so here is an example how not to do things:

use try and catch

try
{
res = Int32.Parse(strVAR)
}
catch(exception ex) 
{
 return null;
}

Answer 6

Do you want to do something like this?

public int? Parse(string categoryID) 
{
  int value;
  if (int.TryParse(categoryID, out value))
  {
    return value;
  }
  else
  {
    return null;
  }
}