Int32.TryParse() returns zero on failure - success or failure?

Question

I read this from msdn about Int32.TryParse()

When this method returns, contains the 32-bit signed integer value equivalent to the number contained in s, if the conversion succeeded, or zero if the conversion failed.

But what happens if the passed string itself is a string representation of '0'. So the TryParse will return zero. How can I know if it is a success or a failure?

Chretien

Answer 1

No, TryParse returns true or false to indicate success. The value of the out parameter is used for the parsed value, or 0 on failure. So:

int value;
if (Int32.TryParse(someText, out value))
{
    // Parse successful. value can be any integer
}
else
{
    // Parse failed. value will be 0.
}

So if you pass in "0", it will execute the first block, whereas if you pass in "bad number" it will execute the second block.

Doall

Gosh! My bad. I should close SO while I'm programming. Its too easy to post here :). – Chretien

You left out a ) at the end of your if.</nitpick> – Abet

Answer 2

The method returns a boolean indicating success or failure. Use that. The integer is a reference parameter passed into the method, and has nothing to do with the return value of the method.

Here's the prototype of Int32.TryParse() from the documentation. It's very clear that it returns a boolean. The second parameter is an out int which means that argument is passed by reference, so it will be mutated by the method.

public static bool TryParse(
    string s,
    out int result
)

So to check success or failure, do this:

int value;

if (Int32.TryParse("0", out value))
    Console.WriteLine("Parsed as " + value);
else
    Console.WriteLine("Could not parse");

Abet

Answer 3

TryParse() returns a Boolean.

        Int32 testInt;

        if (!Int32.TryParse("123", out testInt))
        {
            MessageBox.Show("Is not a Int32!");
            return; // abbrechen
        }

        MessageBox.Show("The parst Int32-value is " + testInt);

Hogwash

Answer 4

using C# 7 now you can declare the variable within the TryParse like ...

if (Int32.TryParse(someText, out int value))
{
   // Parse successful. value can be any integer
}
else
{
   // Parse failed. value will be 0.
}

Shushubert

Answer 5

The Int32.TryParse() method returns a boolean value as return and provides the converted value as an out parameter. So you can check for the return boolean value for the status.

private static void TryToParse(string value)
   {
      int number;
      bool result = Int32.TryParse(value, out number);
      if (result)
      {
         Console.WriteLine("Converted '{0}' to {1}.", value, number);         
      }
      else
      {
         if (value == null) value = ""; 
         Console.WriteLine("Attempted conversion of '{0}' failed.", value);
      }
   }

Cofsky

Answer 6

My favorite and shortest;

int number = Int32.TryParse(TheValueToConvert, out int n) ? n : 0;

Returns the converted integer, otherwise 0

Crossover

Int32.TryParse will set the int value to 0 when it fails, anyway. This method is good when you need a value other than 0 when the TryParse fails. – Thermocline