Convert.ToUInt16 Method (String, Int32)

July 28, 2014

Converts the string representation of a number in a specified base to an equivalent 16-bit unsigned integer.

This API is not CLS-compliant. 

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

[CLSCompliantAttribute(false)]
public static ushort ToUInt16(
	string value,
	int fromBase
)

Parameters

value
Type: System.String
A string containing a number.
fromBase
Type: System.Int32
The base of the number in value, which must be 2, 8, 10, or 16.

Return Value

Type: System.UInt16
A 16-bit unsigned integer equivalent to the number in value.
-or-
Zero if value is null.

ExceptionCondition
ArgumentException

fromBase is not 2, 8, 10, or 16.

-or-

value, which represents a non-base 10 unsigned number, is prefixed with a negative sign.

FormatException

value contains a character that is not a valid digit in the base specified by fromBase. The exception message indicates that there are no digits to convert if the first character in value is invalid; otherwise, the message indicates that value contains invalid trailing characters.

OverflowException

value, which represents a non-base 10 unsigned number, is prefixed with a negative sign.

-or-

The return value is less than UInt16.MinValue or larger than UInt16.MaxValue.

If fromBase is 16, you can prefix the number specified by the value parameter with "0x" or "0X".

Because the UInt16 data type supports unsigned values only, the ToUInt16(String, Int32) method assumes that value is expressed using unsigned binary representation. In other words, all sixteen bits are used to represent the numeric value and a sign bit is absent. As a result, it is possible to write code in which a signed integer value that is out of the range of the UInt16 data type is converted to a UInt16 value without the method throwing an exception. The following example converts MinValue to its hexadecimal string representation and then calls the ToUInt16(String, Int32) method. Rather than throwing an exception, the method displays the message, "0x8000 converts to 32768."


// Create a hexadecimal value out of range of the UInt16 type.
string value = Convert.ToString(Int16.MinValue, 16);
// Convert it back to a number.
try
{
   UInt16 number = Convert.ToUInt16(value, 16);
   outputBlock.Text += String.Format("0x{0} converts to {1}.", value, number) + "\n";
}
catch (OverflowException)
{
   outputBlock.Text += String.Format("Unable to convert '0x{0}' to an unsigned short integer.",
                     value) + "\n";
}


When performing binary operations or numeric conversions, it is always the responsibility of the developer to verify that a method or operator uses the appropriate numeric representation to interpret a particular value. The following example illustrates one technique for ensuring that the method does not inappropriately use binary representation to interpret a value that uses two's complement representation when converting a hexadecimal string to a UInt16 value. It determines whether a value represents a signed or an unsigned integer at the same time that it converts that value to its string representation. When converting the value to a UInt16 value, the example checks whether the original value was a signed integer. If so, and its high-order bit is set (which indicates that the original value was negative), the method throws an exception.


// Create a negative hexadecimal value out of range of the UInt16 type.
short sourceNumber = Int16.MinValue;
bool isSigned = Math.Sign((short)sourceNumber.GetType().GetField("MinValue").GetValue(null)) == -1;
string value = Convert.ToString(sourceNumber, 16);
UInt16 targetNumber;
try
{
   targetNumber = Convert.ToUInt16(value, 16);
   if (isSigned && ((targetNumber & 0x8000) != 0))
      throw new OverflowException();
   else
      outputBlock.Text += String.Format("0x{0} converts to {1}.", value, targetNumber) + "\n";
}
catch (OverflowException)
{
   outputBlock.Text += String.Format("Unable to convert '0x{0}' to an unsigned short integer.", value) + "\n";
}
// Displays the following:
//    Unable to convert '0x8000' to an unsigned short integer.     


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

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