Convert.ToInt32 Method (String, Int32)

Converts the string representation of a number in a specified base to an equivalent 32-bit signed integer.

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

public static int ToInt32(
	string value,
	int fromBase
)

Parameters

value
Type: System.String

A string that contains the number to convert.

fromBase
Type: System.Int32

The base of the number in value, which must be 2, 8, 10, or 16.

Return Value

Type: System.Int32
A 32-bit signed integer that is equivalent to the number in value, or 0 (zero) if value is null.

ExceptionCondition
ArgumentException

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

-or-

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

ArgumentOutOfRangeException

value is String.Empty.

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 signed number, is prefixed with a negative sign.

-or-

value represents a number that is less than Int32.MinValue or greater than Int32.MaxValue.

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

Because the negative sign is not supported for non-base 10 numeric representations, the ToInt32(String, Int32) method assumes that negative numbers use two’s complement representation. In other words, the method always interprets the highest-order binary bit of an integer (bit 31) as its sign bit. As a result, it is possible to write code in which a non-base 10 number that is out of the range of the Int32 data type is converted to an Int32 value without the method throwing an exception. The following example increments Int32.MaxValue by one, converts the resulting number to its hexadecimal string representation, and then calls the ToInt32(String, Int32) method. Instead of throwing an exception, the method displays the message, "0x80000000 converts to -2147483648."

// Create a hexadecimal value out of range of the Integer type. 
string value = Convert.ToString((long) int.MaxValue + 1, 16);
// Convert it back to a number. 
try
{
   int number = Convert.ToInt32(value, 16);
   Console.WriteLine("0x{0} converts to {1}.", value, number.ToString());
}
catch (OverflowException)
{
   Console.WriteLine("Unable to convert '0x{0}' to an integer.", value);
}   

When performing binary operations or numeric conversions, it is always the responsibility of the developer to verify that a method is using the appropriate numeric representation to interpret a particular value. As the following example illustrates, you can ensure that the method handles overflows appropriately by first retrieving the sign of the numeric value before converting it to its hexadecimal string representation. Throw an exception if the original value was positive but the conversion back to an integer yields a negative value.

// Create a hexadecimal value out of range of the Integer type. 
long sourceNumber = (long) int.MaxValue + 1;
bool isNegative = Math.Sign(sourceNumber) == -1;
string value = Convert.ToString(sourceNumber, 16);
int targetNumber;
try
{
   targetNumber = Convert.ToInt32(value, 16);
   if (!(isNegative) & (targetNumber & 0x80000000) != 0) 
      throw new OverflowException();
   else 
      Console.WriteLine("0x{0} converts to {1}.", value, targetNumber);
}
catch (OverflowException)
{
   Console.WriteLine("Unable to convert '0x{0}' to an integer.", value);
} 
// Displays the following to the console: 
//    Unable to convert '80000000' to an integer.     

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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