Convert.ToInt32 Method (String, Int32)


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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


Type: System.String

A string that contains the number to convert.

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.

Exception Condition

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


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


value is String.Empty.


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.


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


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.
   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;
   targetNumber = Convert.ToInt32(value, 16);
   if (!(isNegative) & (targetNumber & 0x80000000) != 0) 
      throw new OverflowException();
      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 '0x80000000' to an integer.    

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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