Represent Int64 as a Hexadecimal String in C#

To represent Int64 as a hexadecimal string in C#, use the Convert.ToString() method and set the base as 16 for hexadecimal conversion. Int64 represents a 64-bit signed integer that can hold values from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.

Syntax

Following is the syntax for converting Int64 to hexadecimal string −

Convert.ToString(longValue, 16)

You can also use the ToString() method with format specifiers −

longValue.ToString("X")   // Uppercase hex
longValue.ToString("x")   // Lowercase hex

Using Convert.ToString() Method

The Convert.ToString() method with base 16 converts an Int64 value to its hexadecimal representation −

using System;

class Demo {
    static void Main() {
        long val = 947645;
        Console.WriteLine("Long: " + val);
        Console.WriteLine("Hex String: " + Convert.ToString(val, 16));
        
        // Testing with negative number
        long negVal = -123456;
        Console.WriteLine("Negative Long: " + negVal);
        Console.WriteLine("Hex String: " + Convert.ToString(negVal, 16));
    }
}

The output of the above code is −

Long: 947645
Hex String: e75bd
Negative Long: -123456
Hex String: fffffffffffe1dc0

Using ToString() with Format Specifiers

The ToString() method with format specifiers provides more control over the hexadecimal output format −

using System;

class Demo {
    static void Main() {
        long val = 255;
        
        Console.WriteLine("Value: " + val);
        Console.WriteLine("Uppercase hex: " + val.ToString("X"));
        Console.WriteLine("Lowercase hex: " + val.ToString("x"));
        Console.WriteLine("8-digit hex: " + val.ToString("X8"));
        Console.WriteLine("16-digit hex: " + val.ToString("X16"));
    }
}

The output of the above code is −

Value: 255
Uppercase hex: FF
Lowercase hex: ff
8-digit hex: 000000FF
16-digit hex: 00000000000000FF

Comparison of Methods

Working with Large Int64 Values

Here's an example with maximum and minimum Int64 values −

using System;

class Demo {
    static void Main() {
        long maxVal = Int64.MaxValue;
        long minVal = Int64.MinValue;
        
        Console.WriteLine("Max Int64: " + maxVal);
        Console.WriteLine("Max as hex: " + Convert.ToString(maxVal, 16));
        
        Console.WriteLine("Min Int64: " + minVal);
        Console.WriteLine("Min as hex: " + Convert.ToString(minVal, 16));
    }
}

The output of the above code is −

Max Int64: 9223372036854775807
Max as hex: 7fffffffffffffff
Min Int64: -9223372036854775808
Min as hex: 8000000000000000

Conclusion

Converting Int64 to hexadecimal in C# can be accomplished using Convert.ToString(value, 16) for basic conversion or ToString("X") for more formatting control. Both methods handle negative numbers by using two's complement representation in the hexadecimal output.