Convert a c# string with year only (sometimes) to datetime

Question

The program needs to find the youngest (or oldest) person within a list. The birthday is actually a string. I converted the dates using Convert.ToDateTime(), which is working fine. However, in a few cases, the input is just a year, without the day and the month, e.g. "1945". The converter fails.

My questions:

1) what checker can I add in order to prevent such a run-time failure?

2) How can I convert it to date, without overriding strings that include the day and the month? the code is:

DateTime curr_bday = Convert.ToDateTime(p.Birthday);

here is the full routine:

public string the_youngest(Persons _p2)
{
    DateTime youngAge = Convert.ToDateTime("01/01/1005");

    DateTime curr_bday;
    string to_ret = "";

    foreach (var p in _p2.persons)
    {
        curr_bday = Convert.ToDateTime(p.Birthday);
        if (curr_bday < youngAge)
        {
            youngAge = curr_bday;
            to_ret = p.Name + " : " + p.Birthday;
        } 
    }
    return (to_ret);
}

Where are these strings coming from, and can you give us a few examples? — Dour High Arch
– Dour High Arch, Commented Mar 21, 2019 at 18:17
Test to see if the string is an integer with int.TryParse. If it is, initialize your birthday variable with a newly constructed DateTime where you specify only the year. Otherwise, parse the string as a date time — Flydog57
– Flydog57, Commented Mar 21, 2019 at 18:17
@ Flydog57 : it looks like it is working well. I had a bug in the compare part (bigger birhday means younger person) Thank you ! — YigalB
– YigalB, Commented Mar 21, 2019 at 18:43

Ramy Moussa · Accepted Answer · 2019-03-21 18:24:10Z

1

Explore the TryParse function. it works with dates, integers, and decimals.

DateTime birthdate;
if(DateTime.TryParse(p.Birthday, out birthdate))
{
  //full date here successfully converted
  //continue
}
else
{
   birthdate = new DateTime(Int32.Parse(p.Birthday), 1, 1); //1 Jan by default
}

answered Mar 21, 2019 at 18:24

Ramy Moussa

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Comments

Flydog57 · Accepted Answer · 2019-03-21 18:28:22Z

1

Using TryParse all over is your best bet:

DateTime bDay;
if (int.TryParse(dateString, out var birthYear))
{
    dateString = new DateTime(birthYear, 7, 4); //born on the 4th of July
}
else if (!DateTime.TryParse( dateString, out bDay))
{
    //let the user know there's a problem
}

answered Mar 21, 2019 at 18:28

Flydog57

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1 Comment

Mong Zhu Over a year ago

most stable and concise solution here, have an upvote! ;)

Steve · Accepted Answer · 2019-03-21 18:18:58Z

0

Assuming the only two possible formats are {year} and {valid datetime} string then you can do

DateTime d;
if (p.Birthday.Length <= 4)
{
     int year = int.Parse(p.Birthday);
     d = new DateTime(year, 1, 1);
}
else
{
     d = DateTime.Parse(p.Birthday)
}

This will work for another 8000 years. However if there are other special case then you need to handle those separately.

answered Mar 21, 2019 at 18:18

Steve

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1 Comment

Flydog57 Over a year ago

You are better off using int.TryParse in the if statement. What about "3/21" (today). It's four characters, and I believe it would be a valid date in a US copy of Excel

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