Question

See the following code:

string test = "";
int output = -1;

if (int.TryParse(test, out output))
{
    Console.WriteLine("Parsed");
}

Console.WriteLine(output);

When TryParse() fails, shouldn’t the block be skipped over, Console.WriteLine("Parsed") not called and the value of output be the same (-1)?

It’s returning 0

Answer 1

The implementation of TryParse has to default the out parameter before returning otherwise it won’t compile – regardless of whether you have initialised the out parameter from the calling side. This is the case for any method with out parameters and is not specific to TryParse.

The people who coded it chose to default the parameter to zero when the parsing fails.

The important part is you should not think that any out parameter methods will honour the original value of the out parameter when it is passed in. In fact, it can never honour the parameter as the compiler will report:

use of unassigned out parameter ‘blah’

If you attempt to use the parameter value before assigning to it inside the method. So you can actually guarantee that any value you assign and give to as an out parameter will be ignored / overwritten.