DateTime Functions in C# and .NET

In .NET, what is DateTime?
A.NET struct called DateTime is used to express dates and times with a precision of 100 ticks, or nanoseconds. System Assembly namespace: mscorlib.dll

Creating DateTime Instances

// Current date and time (system clock)
DateTime now = DateTime.Now;

// Current UTC time
DateTime utcNow = DateTime.UtcNow;

// Only current date, time set to 00:00:00
DateTime today = DateTime.Today;

// Specific date
DateTime specificDate = new DateTime(2025, 9, 8); // YYYY, MM, DD

// Specific date and time
DateTime specificDateTime = new DateTime(2025, 9, 8, 14, 30, 0); // YYYY,MM,DD,HH,MM,SS

Properties of DateTime

Property	Description	Example
Date	Returns the date part only (time = 00:00:00)	now.Date
Day	Day of the month (1-31)	now.Day
Month	Month (1-12)	now.Month
Year	Year component	now.Year
DayOfWeek	Enum representing day of week	DayOfWeek.Monday
DayOfYear	Day number in the year (1-366)	now.DayOfYear
TimeOfDay	Returns a TimeSpan	now.TimeOfDay
Hour, Minute, Second, Millisecond	Components of time	now.Hour

Common DateTime Methods

🧾Static Methods

DateTime current = DateTime.Now;

// Parsing
DateTime parsed = DateTime.Parse("2025-09-08");
DateTime parsedExact = DateTime.ParseExact("08-09-2025", "dd-MM-yyyy", null);

// Comparing
int result = DateTime.Compare(DateTime.Now, DateTime.UtcNow); // -1, 0, 1

// Check Leap Year
bool isLeap = DateTime.IsLeapYear(2024);

Instance Methods for Manipulation

DateTime today = DateTime.Today;

DateTime tomorrow = today.AddDays(1);       // Add days
DateTime lastWeek = today.AddDays(-7);      // Subtract days
DateTime nextMonth = today.AddMonths(1);    // Add months
DateTime lastYear = today.AddYears(-1);     // Subtract years
DateTime futureTime = today.AddHours(5);    // Add hours

Comparison Methods

DateTime a = DateTime.Now;
DateTime b = a.AddMinutes(10);

bool isEqual = a.Equals(b);    // false
int compare = a.CompareTo(b);  // -1 (a < b)

bool after = a > b;            // false
bool before = a < b;           // true

Formatting Methods

DateTime now = DateTime.Now;

// ToString with custom format
string formatted = now.ToString("dd/MM/yyyy HH:mm:ss");

// Predefined formats
string longDate = now.ToLongDateString();  // Monday, September 8, 2025
string shortDate = now.ToShortDateString(); // 9/8/2025
string longTime = now.ToLongTimeString();  // 4:25:30 PM
string shortTime = now.ToShortTimeString(); // 4:25 PM

Time Zones

DateTime utcNow = DateTime.UtcNow;

// Convert to local time
DateTime local = utcNow.ToLocalTime();

// Specify kind explicitly
DateTime unspecified = DateTime.SpecifyKind(utcNow, DateTimeKind.Unspecified);

DateTimeOffset (Recommended for Modern Apps)

DateTimeOffset is often preferred because it stores both the date/time and the UTC offset, which avoids ambiguity when working across multiple time zones.

DateTimeOffset dto = DateTimeOffset.Now;
Console.WriteLine(dto.Offset); // e.g., +05:30

Best Practices

• Prefer DateTime.UtcNow for logging, auditing, and storage — avoid timezone issues.

• Use DateTimeOffset when time zones matter (multi-region apps).

• Use TryParse or TryParseExact for safe conversions (avoid exceptions).

• Always specify a format when serializing dates (ISO 8601 recommended: "yyyy-MM-ddTHH:mm:ssZ").

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