DateTime.Parse() / DateTime.TryParse()

DateTime dt = DateTime.Parse(string s);

// Attempts conversion and returns true on success or false on failure (no exception).
bool success = DateTime.TryParse(string s, out DateTime result);

// Converts using a specified format.
DateTime dt = DateTime.ParseExact(string s, string format, IFormatProvider provider);
bool success = DateTime.TryParseExact(string s, string format, IFormatProvider provider, DateTimeStyles style, out DateTime result);

Program.cs

using System;
using System.Globalization;

// Convert using DateTime.Parse().
DateTime dt1 = DateTime.Parse("2024/01/15");
Console.WriteLine(dt1); // 1/15/2024 12:00:00 AM

DateTime dt2 = DateTime.Parse("2024-03-20 14:30:00");
Console.WriteLine(dt2); // 3/20/2024 2:30:00 PM

// Convert safely using TryParse() (recommended for user input).
string input = "2024/06/01";
if (DateTime.TryParse(input, out DateTime result))
{
    Console.WriteLine($"Converted: {result:yyyy/M/d}");
}
else
{
    Console.WriteLine("Conversion failed.");
}

// A string that cannot be converted returns false.
bool ok = DateTime.TryParse("abc", out DateTime failResult);
Console.WriteLine($"Success: {ok}"); // False

// Specify a strict format using ParseExact().
DateTime dt3 = DateTime.ParseExact("20240115", "yyyyMMdd", CultureInfo.InvariantCulture);
Console.WriteLine(dt3); // 1/15/2024 12:00:00 AM

// Example using TryParseExact().
bool parseOk = DateTime.TryParseExact(
    "15-01-2024",
    "dd-MM-yyyy",
    CultureInfo.InvariantCulture,
    DateTimeStyles.None,
    out DateTime dt4
);
Console.WriteLine($"Success: {parseOk}, Result: {dt4:yyyy/MM/dd}");

Run the following command:

dotnet script datetime_parse_tryparse.csx
1/15/2024 12:00:00 AM
3/20/2024 2:30:00 PM
Converted: 2024/6/1
Success: False
1/15/2024 12:00:00 AM
Success: True, Result: 2024/01/15

User-entered date strings can have unpredictable formats, so use TryParse with error handling. This example tries multiple formats.

FormInputParse.cs

using System;
using System.Globalization;

// Parses a user-entered date string.
static bool TryParseDate(string input, out DateTime date)
{
    // Tries multiple formats.
    string[] formats = { "yyyy/MM/dd", "yyyy-MM-dd", "yyyyMMdd", "MM/dd/yyyy" };
    return DateTime.TryParseExact(
        input,
        formats,
        CultureInfo.InvariantCulture,
        DateTimeStyles.None,
        out date
    );
}

// Test: activity log dates for Rintaro Okabe
string[] inputs = { "2024/01/15", "2024-03-20", "20240601", "invalid" };
foreach (string s in inputs)
{
    if (TryParseDate(s, out DateTime parsed))
        Console.WriteLine($"[OK] {s} → {parsed:yyyy/M/d}");
    else
        Console.WriteLine($"[NG] {s} → Conversion failed");
}

Run the following command:

dotnet script form_input_parse.csx
[OK] 2024/01/15 → 2024/1/15
[OK] 2024-03-20 → 2024/3/20
[OK] 20240601 → 2024/6/1
[NG] invalid → Conversion failed

When extracting dates from log filenames or similar sources with a fixed format, ParseExact is the right tool.

FileNameParse.cs

using System;
using System.Globalization;

// Extracts dates from log filenames (e.g., log_20240115.txt).
string[] fileNames = { "log_20240115.txt", "log_20240316.txt", "log_20241231.txt" };

foreach (string fileName in fileNames)
{
    // Extracts the 8-digit date portion from the filename.
    string datePart = fileName.Replace("log_", "").Replace(".txt", "");
    DateTime fileDate = DateTime.ParseExact(datePart, "yyyyMMdd", CultureInfo.InvariantCulture);

    // Determines whether the file is 30 or more days old.
    TimeSpan diff = DateTime.Today - fileDate;
    bool isOld = diff.TotalDays >= 30;
    Console.WriteLine($"{fileName}: {fileDate:yyyy/MM/dd} → {(isOld ? "Delete" : "Keep")}");
}

Run the following command:

dotnet script filename_parse.csx
log_20240115.txt: 2024/01/15 → Delete
log_20240316.txt: 2024/03/16 → Delete
log_20241231.txt: 2024/12/31 → Keep

Common Mistake 1: Parse() Throws an Exception

DateTime.Parse() throws a FormatException when parsing fails. Use TryParse for user input and external data.

using System;

// NG: Using Parse() on user input can throw an exception.
string userInput = "January 15, 2024 (unknown format)";
DateTime dt = DateTime.Parse(userInput); // FormatException is thrown.

Run the following command:

dotnet run
Unhandled exception. System.FormatException: String 'January 15, 2024 (unknown format)' was not recognized as a valid DateTime.

The following example demonstrates this:

using System;

// OK: TryParse() handles failure without throwing an exception.
string userInput = "January 15, 2024 (unknown format)";
if (DateTime.TryParse(userInput, out DateTime dt))
    Console.WriteLine($"Converted: {dt}");
else
    Console.WriteLine("Conversion failed. Please check the input format.");

Run the following command:

dotnet run
Conversion failed. Please check the input format.

Common Mistake 2: Omitting CultureInfo

ParseExact uses the current culture when CultureInfo is omitted. Formats containing English month names such as "Jan" may fail to parse in non-English environments unless CultureInfo.InvariantCulture is specified.

using System;
using System.Globalization;

// NG: "Jan" may not be recognized as a month name in non-English environments.
// DateTime.ParseExact("15-Jan-2024", "dd-MMM-yyyy", null);

// OK: Specify CultureInfo.InvariantCulture to ensure locale-independent parsing.
DateTime dt = DateTime.ParseExact(
    "15-Jan-2024",
    "dd-MMM-yyyy",
    CultureInfo.InvariantCulture
);
Console.WriteLine(dt); // 1/15/2024 12:00:00 AM

Run the following command:

dotnet run
1/15/2024 12:00:00 AM

When converting strings from user input or files to DateTime, use TryParse() or TryParseExact(), which do not throw exceptions. Use Parse() only for strings with a guaranteed format, such as constants or database values.

When the format is fixed to a specific pattern (such as filenames in yyyyMMdd format), ParseExact() is convenient. Specifying CultureInfo.InvariantCulture ensures locale-independent conversion.

For formatting a DateTime value after conversion, see DateTime.ToString() / DateTime.AddDays().