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Tradução
Inglês

Estrutura Single

 

Representa um número de ponto flutuante de precisão simples.

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

[SerializableAttribute]
[ComVisibleAttribute(true)]
public struct Single : IComparable, IFormattable, IConvertible, 
	IComparable<float>, IEquatable<float>

NomeDescrição
System_CAPS_pubmethodCompareTo(Object)

Compara esta instância a um objeto especificado e retorna um inteiro que indica se o valor desta instância é menor, igual ou maior que o valor do objeto especificado.

System_CAPS_pubmethodCompareTo(Single)

Compara essa instância a um número de ponto flutuante de precisão simples especificado e retorna um inteiro que indica se o valor dessa instância é menor que, igual a ou maior que o valor do número de ponto flutuante de precisão simples especificado.

System_CAPS_pubmethodEquals(Object)

Retorna um valor que indica se esta instância é igual ao objeto especificado.(Substitui o ValueType.Equals(Object).)

System_CAPS_pubmethodEquals(Single)

Retorna um valor que indica se essa instância e um objeto Single especificado representam o mesmo valor.

System_CAPS_pubmethodGetHashCode()

Retorna o hash code para essa instância. (Substitui o ValueType.GetHashCode().)

System_CAPS_pubmethodGetType()

Obtém o Type da instância atual.(Herdado de Object.)

System_CAPS_pubmethodGetTypeCode()

Retorna o TypeCode para tipo de valor Single.

System_CAPS_pubmethodSystem_CAPS_staticIsInfinity(Single)

Retorna um valor que indica se o número especificado é avaliada como infinito positivo ou negativo.

System_CAPS_pubmethodSystem_CAPS_staticIsNaN(Single)

Retorna um valor que indica se o valor especificado não é um número (NaN).

System_CAPS_pubmethodSystem_CAPS_staticIsNegativeInfinity(Single)

Retorna um valor que indica se o número especificado é avaliada como infinito negativo.

System_CAPS_pubmethodSystem_CAPS_staticIsPositiveInfinity(Single)

Retorna um valor que indica se o número especificado é avaliada como infinito positivo.

System_CAPS_pubmethodSystem_CAPS_staticParse(String)

Converte a representação da cadeia de caracteres de um número no número de ponto flutuante de precisão simples equivalente.

System_CAPS_pubmethodSystem_CAPS_staticParse(String, IFormatProvider)

Converte a representação de cadeia de caracteres de um número em um formato específico da cultura para o número de ponto flutuante de precisão simples equivalente.

System_CAPS_pubmethodSystem_CAPS_staticParse(String, NumberStyles)

Converte a representação de cadeia de caracteres de um número em um estilo especificado para o número de ponto flutuante de precisão simples equivalente.

System_CAPS_pubmethodSystem_CAPS_staticParse(String, NumberStyles, IFormatProvider)

Converte a representação de cadeia de caracteres de um número em um estilo e formato específico da cultura especificados em seu equivalente de número de ponto flutuante de precisão simples.

System_CAPS_pubmethodToString()

Converte o valor numérico dessa instância na representação da cadeia de caracteres equivalente.(Substitui o ValueType.ToString().)

System_CAPS_pubmethodToString(IFormatProvider)

Converte o valor numérico dessa instância na representação da cadeia de caracteres equivalente usando as informações de formato específicas da cultura especificada.

System_CAPS_pubmethodToString(String)

Converte o valor numérico dessa instância na representação da cadeia de caracteres equivalente usando o formato especificado.

System_CAPS_pubmethodToString(String, IFormatProvider)

Converte o valor numérico dessa instância na representação da cadeia de caracteres equivalente usando o formato especificado e as informações de formato específicas da cultura especificada.

System_CAPS_pubmethodSystem_CAPS_staticTryParse(String, NumberStyles, IFormatProvider, Single)

Converte a representação de cadeia de caracteres de um número em um estilo e formato específico da cultura especificados em seu equivalente de número de ponto flutuante de precisão simples. Um valor de retorno indica se a conversão foi bem-sucedida ou falhou.

System_CAPS_pubmethodSystem_CAPS_staticTryParse(String, Single)

Converte a representação da cadeia de caracteres de um número no número de ponto flutuante de precisão simples equivalente. Um valor de retorno indica se a conversão foi bem-sucedida ou falhou.

NomeDescrição
System_CAPS_pubfieldSystem_CAPS_staticEpsilon

Representa o menor valor Single positivo maior que zero. Este campo é constante.

System_CAPS_pubfieldSystem_CAPS_staticMaxValue

Representa o maior valor possível de Single. Este campo é constante.

System_CAPS_pubfieldSystem_CAPS_staticMinValue

Representa o menor valor possível de Single. Este campo é constante.

System_CAPS_pubfieldSystem_CAPS_staticNaN

Representa algo que não é um número (NaN). Este campo é constante.

System_CAPS_pubfieldSystem_CAPS_staticNegativeInfinity

Representa negativo infinito. Esse campo é constante.

System_CAPS_pubfieldSystem_CAPS_staticPositiveInfinity

Representa infinito positivo. Este campo é constante.

NomeDescrição
System_CAPS_puboperatorSystem_CAPS_staticEquality(Single, Single)

Retorna um valor que indica se dois especificada Single valores são iguais.

System_CAPS_puboperatorSystem_CAPS_staticGreaterThan(Single, Single)

Retorna um valor que indica se um Single valor é maior que outro especificado Single valor.

System_CAPS_puboperatorSystem_CAPS_staticGreaterThanOrEqual(Single, Single)

Retorna um valor que indica se um Single valor é maior que ou igual a outro especificado Single valor.

System_CAPS_puboperatorSystem_CAPS_staticInequality(Single, Single)

Retorna um valor que indica se dois especificada Single valores não são iguais.

System_CAPS_puboperatorSystem_CAPS_staticLessThan(Single, Single)

Retorna um valor que indica se um Single valor é menor que outro especificado Single valor.

System_CAPS_puboperatorSystem_CAPS_staticLessThanOrEqual(Single, Single)

Retorna um valor que indica se um Single valor é menor ou igual a outro especificado Single valor.

NomeDescrição
System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToBoolean(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToBoolean.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToByte(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToByte.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToChar(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Não há suporte para essa conversão. Tentativa de usar esse método lança um InvalidCastException.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToDateTime(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Não há suporte para essa conversão. Tentativa de usar esse método lança um InvalidCastException.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToDecimal(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToDecimal.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToDouble(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToDouble.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToInt16(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToInt16.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToInt32(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToInt32.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToInt64(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToInt64.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToSByte(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToSByte.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToSingle(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToSingle.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToType(Type, IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToType.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToUInt16(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToUInt16.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToUInt32(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToUInt32.

System_CAPS_pubinterfaceSystem_CAPS_privmethodIConvertible.ToUInt64(IFormatProvider)

Esta API dá suporte à infraestrutura produto e não se destina a ser usada diretamente do seu código. Para obter uma descrição desse membro, consulte IConvertible.ToUInt64.

The T:System.Single value type represents a single-precision 32-bit number with values ranging from negative 3.402823e38 to positive 3.402823e38, as well as positive or negative zero, F:System.Single.PositiveInfinity, F:System.Single.NegativeInfinity, and not a number (F:System.Single.NaN). It is intended to represent values that are extremely large (such as distances between planets or galaxies) or extremely small (such as the molecular mass of a substance in kilograms) and that often are imprecise (such as the distance from earth to another solar system). The T:System.Single type complies with the IEC 60559:1989 (IEEE 754) standard for binary floating-point arithmetic.

This topic consists of the following sections:

System.Single provides methods to compare instances of this type, to convert the value of an instance to its string representation, and to convert the string representation of a number to an instance of this type. For information about how format specification codes control the string representation of value types, see Formatando tipos no .NET Framework, Cadeias de caracteres de formato numérico padrão, and Cadeias de caracteres de formato numérico personalizado.

The T:System.Single data type stores single-precision floating-point values in a 32-bit binary format, as shown in the following table:

Part

Bits

Significand or mantissa

0-22

Exponent

23-30

Sign (0 = positive, 1 = negative)

31

Just as decimal fractions are unable to precisely represent some fractional values (such as 1/3 or F:System.Math.PI), binary fractions are unable to represent some fractional values. For example, 2/10, which is represented precisely by .2 as a decimal fraction, is represented by .0011111001001100 as a binary fraction, with the pattern "1100" repeating to infinity. In this case, the floating-point value provides an imprecise representation of the number that it represents. Performing additional mathematical operations on the original floating-point value often increases its lack of precision. For example, if you compare the results of multiplying .3 by 10 and adding .3 to .3 nine times, you will see that addition produces the less precise result, because it involves eight more operations than multiplication. Note that this disparity is apparent only if you display the two T:System.Single values by using the "R" standard numeric format string, which, if necessary, displays all 9 digits of precision supported by the T:System.Single type.

using System;

public class Example
{
   public static void Main()
   {
      Single value = .2f;
      Single result1 = value * 10f;
      Single result2 = 0f;
      for (int ctr = 1; ctr <= 10; ctr++)
         result2 += value;

      Console.WriteLine(".2 * 10:           {0:R}", result1);
      Console.WriteLine(".2 Added 10 times: {0:R}", result2);
   }
}
// The example displays the following output:
//       .2 * 10:           2
//       .2 Added 10 times: 2.00000024

Because some numbers cannot be represented exactly as fractional binary values, floating-point numbers can only approximate real numbers.

All floating-point numbers have a limited number of significant digits, which also determines how accurately a floating-point value approximates a real number. A T:System.Single value has up to 7 decimal digits of precision, although a maximum of 9 digits is maintained internally. This means that some floating-point operations may lack the precision to change a floating-point value. The following example defines a large single-precision floating-point value, and then adds the product of F:System.Single.Epsilon and one quadrillion to it. However, the product is too small to modify the original floating-point value. Its least significant digit is thousandths, whereas the most significant digit in the product is 1-312.

using System;

public class Example
{
   public static void Main()
   {
      Single value = 123456789e4f;
      Single additional = Single.Epsilon * 1e12f;
      Console.WriteLine("{0} + {1} = {2}", value, additional, 
                                           value + additional);
   }
}
// The example displays the following output:
//    1.234568E+12 + 1.401298E-33 = 1.234568E+12

The limited precision of a floating-point number has several consequences:

  • Two floating-point numbers that appear equal for a particular precision might not compare equal because their least significant digits are different. In the following example, a series of numbers are added together, and their total is compared with their expected total. Although the two values appear to be the same, a call to the Equals method indicates that they are not.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Single[] values = { 10.01f, 2.88f, 2.88f, 2.88f, 9.0f };
          Single result = 27.65f;
          Single total = 0f;
          foreach (var value in values)
             total += value;
    
          if (total.Equals(result))
             Console.WriteLine("The sum of the values equals the total.");
          else
             Console.WriteLine("The sum of the values ({0:R}) does not equal the total ({1:R}).",
                               total, result); 
       }
    }
    // The example displays the following output:
    //      The sum of the values (27.65) does not equal the total (27.65).   
    //
    // If the index items in the Console.WriteLine statement are changed to {0:R},
    // the example displays the following output:
    //       The sum of the values (27.6500015) does not equal the total (27.65).   
    

    If you change the format items in the M:System.Console.WriteLine(System.String,System.Object,System.Object) statement from {0} and {1} to {0:R} and {1:R} to display all significant digits of the two T:System.Single values, it is clear that the two values are unequal because of a loss of precision during the addition operations. In this case, the issue can be resolved by calling the M:System.Math.Round(System.Double,System.Int32) method to round the T:System.Single values to the desired precision before performing the comparison.

  • A mathematical or comparison operation that uses a floating-point number might not yield the same result if a decimal number is used, because the binary floating-point number might not equal the decimal number. A previous example illustrated this by displaying the result of multiplying .3 by 10 and adding .3 to .3 nine times.

    When accuracy in numeric operations with fractional values is important, use the T:System.Decimal type instead of the T:System.Single type. When accuracy in numeric operations with integral values beyond the range of the T:System.Int64 or T:System.UInt64 types is important, use the T:System.Numerics.BigInteger type.

  • A value might not round-trip if a floating-point number is involved. A value is said to round-trip if an operation converts an original floating-point number to another form, an inverse operation transforms the converted form back to a floating-point number, and the final floating-point number is equal to the original floating-point number. The round trip might fail because one or more least significant digits are lost or changed in a conversion. In the following example, three T:System.Single values are converted to strings and saved in a file. As the output shows, although the values appear to be identical, the restored values are not equal to the original values.

    using System;
    using System.IO;
    
    public class Example
    {
       public static void Main()
       {
          StreamWriter sw = new StreamWriter(@".\Singles.dat");
          Single[] values = { 3.2f/1.11f, 1.0f/3f, (float) Math.PI };
          for (int ctr = 0; ctr < values.Length; ctr++) {
             sw.Write(values[ctr].ToString());
             if (ctr != values.Length - 1)
                sw.Write("|");
          }      
          sw.Close();
    
          Single[] restoredValues = new Single[values.Length];
          StreamReader sr = new StreamReader(@".\Singles.dat");
          string temp = sr.ReadToEnd();
          string[] tempStrings = temp.Split('|');
          for (int ctr = 0; ctr < tempStrings.Length; ctr++)
             restoredValues[ctr] = Single.Parse(tempStrings[ctr]);   
    
    
          for (int ctr = 0; ctr < values.Length; ctr++)
             Console.WriteLine("{0} {2} {1}", values[ctr], 
                               restoredValues[ctr],
                               values[ctr].Equals(restoredValues[ctr]) ? "=" : "<>");
       }
    }
    // The example displays the following output:
    //       2.882883 <> 2.882883
    //       0.3333333 <> 0.3333333
    //       3.141593 <> 3.141593
    

    In this case, the values can be successfully round-tripped by using the "R" standard numeric format string to preserve the full precision of T:System.Single values, as the following example shows.

    using System;
    using System.IO;
    
    public class Example
    {
       public static void Main()
       {
          StreamWriter sw = new StreamWriter(@".\Singles.dat");
          Single[] values = { 3.2f/1.11f, 1.0f/3f, (float) Math.PI };
          for (int ctr = 0; ctr < values.Length; ctr++) 
             sw.Write("{0:R}{1}", values[ctr], ctr < values.Length - 1 ? "|" : "" );
    
          sw.Close();
    
          Single[] restoredValues = new Single[values.Length];
          StreamReader sr = new StreamReader(@".\Singles.dat");
          string temp = sr.ReadToEnd();
          string[] tempStrings = temp.Split('|');
          for (int ctr = 0; ctr < tempStrings.Length; ctr++)
             restoredValues[ctr] = Single.Parse(tempStrings[ctr]);   
    
    
          for (int ctr = 0; ctr < values.Length; ctr++)
             Console.WriteLine("{0} {2} {1}", values[ctr], 
                               restoredValues[ctr],
                               values[ctr].Equals(restoredValues[ctr]) ? "=" : "<>");
       }
    }
    // The example displays the following output:
    //       2.882883 = 2.882883
    //       0.3333333 = 0.3333333
    //       3.141593 = 3.141593
    
  • Single values have less precision than Double values. A Single value that is converted to a seemingly equivalent Double often does not equal the Double value because of differences in precision. In the following example, the result of identical division operations is assigned to a Double value and a Single value. After the Single value is cast to a Double, a comparison of the two values shows that they are unequal.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Double value1 = 1/3.0;
          Single sValue2 = 1/3.0f;
          Double value2 = (Double) sValue2;
          Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, 
                                              value1.Equals(value2));
       }
    }
    // The example displays the following output:
    //        0.33333333333333331 = 0.3333333432674408: False
    

    To avoid this problem, either use the T:System.Double data type in place of the T:System.Single data type, or use the M:System.Math.Round(System.Double) method so that both values have the same precision.

To be considered equal, two T:System.Single values must represent identical values. However, because of differences in precision between values, or because of a loss of precision by one or both values, floating-point values that are expected to be identical often turn out to be unequal due to differences in their least significant digits. As a result, calls to the M:System.Single.Equals(System.Single) method to determine whether two values are equal, or calls to the M:System.Single.CompareTo(System.Single) method to determine the relationship between two T:System.Single values, often yield unexpected results. This is evident in the following example, where two apparently equal T:System.Single values turn out to be unequal, because the first value has 7 digits of precision, whereas the second value has 9.

using System;

public class Example
{
   public static void Main()
   {
      float value1 = .3333333f;
      float value2 = 1.0f/3;
      Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, value1.Equals(value2));
   }
}
// The example displays the following output:
//        0.3333333 = 0.333333343: False

Calculated values that follow different code paths and that are manipulated in different ways often prove to be unequal. In the following example, one T:System.Single value is squared, and then the square root is calculated to restore the original value. A second T:System.Single is multiplied by 3.51 and squared before the square root of the result is divided by 3.51 to restore the original value. Although the two values appear to be identical, a call to the M:System.Single.Equals(System.Single) method indicates that they are not equal. Using the "R" standard format string to return a result string that displays all the significant digits of each T:System.Single value shows that the second value is .0000000000001 less than the first.

using System;

public class Example
{
   public static void Main()
   {
      float value1 = 10.201438f;
      value1 = (float) Math.Sqrt((float) Math.Pow(value1, 2));
      float value2 = (float) Math.Pow((float) value1 * 3.51f, 2);
      value2 = ((float) Math.Sqrt(value2)) / 3.51f;
      Console.WriteLine("{0} = {1}: {2}\n", 
                        value1, value2, value1.Equals(value2)); 
      Console.WriteLine("{0:R} = {1:R}", value1, value2); 
   }
}
// The example displays the following output:
//       10.20144 = 10.20144: False
//       
//       10.201438 = 10.2014389

In cases where a loss of precision is likely to affect the result of a comparison, you can use the following techniques instead of calling the M:System.Single.Equals(System.Single) or M:System.Single.CompareTo(System.Single) method:

  • Call the M:System.Math.Round(System.Double) method to ensure that both values have the same precision. The following example modifies a previous example to use this approach so that two fractional values are equivalent.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          float value1 = .3333333f;
          float value2 = 1.0f/3;
          int precision = 7;
          value1 = (float) Math.Round(value1, precision);
          value2 = (float) Math.Round(value2, precision);
          Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, value1.Equals(value2));
       }
    }
    // The example displays the following output:
    //        0.3333333 = 0.3333333: True
    

    Note that the problem of precision still applies to rounding of midpoint values. For more information, see the M:System.Math.Round(System.Double,System.Int32,System.MidpointRounding) method.

  • Test for approximate equality instead of equality. This technique requires that you define either an absolute amount by which the two values can differ but still be equal, or that you define a relative amount by which the smaller value can diverge from the larger value.

    System_CAPS_warningAviso

    Single.Epsilon is sometimes used as an absolute measure of the distance between two Single values when testing for equality. However, Single.Epsilon measures the smallest possible value that can be added to, or subtracted from, a Single whose value is zero. For most positive and negative Single values, the value of Single.Epsilon is too small to be detected. Therefore, except for values that are zero, we do not recommend its use in tests for equality.

    The following example uses the latter approach to define an IsApproximatelyEqual method that tests the relative difference between two values. It also contrasts the result of calls to the IsApproximatelyEqual method and the M:System.Single.Equals(System.Single) method.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          float one1 = .1f * 10;
          float one2 = 0f;
          for (int ctr = 1; ctr <= 10; ctr++)
             one2 += .1f;
    
          Console.WriteLine("{0:R} = {1:R}: {2}", one1, one2, one1.Equals(one2));
          Console.WriteLine("{0:R} is approximately equal to {1:R}: {2}", 
                            one1, one2, 
                            IsApproximatelyEqual(one1, one2, .000001f));   
       }
    
       static bool IsApproximatelyEqual(float value1, float value2, float epsilon)
       {
          // If they are equal anyway, just return True.
          if (value1.Equals(value2))
             return true;
    
          // Handle NaN, Infinity.
          if (Double.IsInfinity(value1) | Double.IsNaN(value1))
             return value1.Equals(value2);
          else if (Double.IsInfinity(value2) | Double.IsNaN(value2))
             return value1.Equals(value2);
    
          // Handle zero to avoid division by zero
          double divisor = Math.Max(value1, value2);
          if (divisor.Equals(0)) 
             divisor = Math.Min(value1, value2);
    
          return Math.Abs(value1 - value2)/divisor <= epsilon;           
       } 
    }
    // The example displays the following output:
    //       1 = 1.00000012: False
    //       1 is approximately equal to 1.00000012: True
    

Operations with floating-point values do not throw exceptions, unlike operations with integral types, which throw exceptions in cases of illegal operations such as division by zero or overflow. Instead, in these situations, the result of a floating-point operation is zero, positive infinity, negative infinity, or not a number (NaN):

  • If the result of a floating-point operation is too small for the destination format, the result is zero. This can occur when two very small floating-point numbers are multiplied, as the following example shows.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          float value1 = 1.163287e-36f;
          float value2 = 9.164234e-25f;
          float result = value1 * value2;
          Console.WriteLine("{0} * {1} = {2}", value1, value2, result);
          Console.WriteLine("{0} = 0: {1}", result, result.Equals(0.0f));
       }
    }
    // The example displays the following output:
    //       1.163287E-36 * 9.164234E-25 = 0
    //       0 = 0: True
    
  • If the magnitude of the result of a floating-point operation exceeds the range of the destination format, the result of the operation is F:System.Single.PositiveInfinity or F:System.Single.NegativeInfinity, as appropriate for the sign of the result. The result of an operation that overflows F:System.Single.MaxValue is F:System.Single.PositiveInfinity, and the result of an operation that overflows F:System.Single.MinValue is F:System.Single.NegativeInfinity, as the following example shows.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          float value1 = 3.065e35f;
          float value2 = 6.9375e32f;
          float result = value1 * value2;
          Console.WriteLine("PositiveInfinity: {0}", 
                             Single.IsPositiveInfinity(result));
          Console.WriteLine("NegativeInfinity: {0}\n", 
                            Single.IsNegativeInfinity(result));
    
          value1 = -value1;
          result = value1 * value2;
          Console.WriteLine("PositiveInfinity: {0}", 
                             Single.IsPositiveInfinity(result));
          Console.WriteLine("NegativeInfinity: {0}", 
                            Single.IsNegativeInfinity(result));
       }
    }                                                                 
    
    // The example displays the following output:
    //       PositiveInfinity: True
    //       NegativeInfinity: False
    //       
    //       PositiveInfinity: False
    //       NegativeInfinity: True
    

    PositiveInfinity also results from a division by zero with a positive dividend, and NegativeInfinity results from a division by zero with a negative dividend.

  • If a floating-point operation is invalid, the result of the operation is F:System.Single.NaN. For example, F:System.Single.NaN results from the following operations:

    • Division by zero with a dividend of zero. Note that other cases of division by zero result in either F:System.Single.PositiveInfinity or F:System.Single.NegativeInfinity.

    • Any floating-point operation with invalid input. For example, attempting to find the square root of a negative value returns F:System.Single.NaN.

    • Any operation with an argument whose value is F:System.Single.NaN.

The T:System.Single structure does not define any explicit or implicit conversion operators; instead, conversions are implemented by the compiler.

The following table lists the possible conversions of a value of the other primitive numeric types to a T:System.Single value, It also indicates whether the conversion is widening or narrowing and whether the resulting T:System.Single may have less precision than the original value.

Conversion from

Widening/narrowing

Possible loss of precision

Byte

Widening

No

Decimal

Widening

Note that C# requires a cast operator.

Yes. T:System.Decimal supports 29 decimal digits of precision; T:System.Single supports 9.

Double

Narrowing; out-of-range values are converted to F:System.Double.NegativeInfinity or F:System.Double.PositiveInfinity.

Yes. T:System.Double supports 17 decimal digits of precision; T:System.Single supports 9.

Int16

Widening

No

Int32

Widening

Yes. T:System.Int32 supports 10 decimal digits of precision; T:System.Single supports 9.

Int64

Widening

Yes. T:System.Int64 supports 19 decimal digits of precision; T:System.Single supports 9.

SByte

Widening

No

UInt16

Widening

No

UInt32

Widening

Yes. T:System.UInt32 supports 10 decimal digits of precision; T:System.Single supports 9.

UInt64

Widening

Yes. T:System.Int64 supports 20 decimal digits of precision; T:System.Single supports 9.

The following example converts the minimum or maximum value of other primitive numeric types to a T:System.Single value.

using System;

public class Example
{
   public static void Main()
   {
      dynamic[] values = { Byte.MinValue, Byte.MaxValue, Decimal.MinValue,
                           Decimal.MaxValue, Double.MinValue, Double.MaxValue,
                           Int16.MinValue, Int16.MaxValue, Int32.MinValue,
                           Int32.MaxValue, Int64.MinValue, Int64.MaxValue,
                           SByte.MinValue, SByte.MaxValue, UInt16.MinValue,
                           UInt16.MaxValue, UInt32.MinValue, UInt32.MaxValue,
                           UInt64.MinValue, UInt64.MaxValue };
      float sngValue;
      foreach (var value in values) {
         if (value.GetType() == typeof(Decimal) ||
             value.GetType() == typeof(Double))
            sngValue = (float) value;
         else
            sngValue = value;
         Console.WriteLine("{0} ({1}) --> {2:R} ({3})",
                           value, value.GetType().Name,
                           sngValue, sngValue.GetType().Name);
      }
   }
}
// The example displays the following output:
//       0 (Byte) --> 0 (Single)
//       255 (Byte) --> 255 (Single)
//       -79228162514264337593543950335 (Decimal) --> -7.92281625E+28 (Single)
//       79228162514264337593543950335 (Decimal) --> 7.92281625E+28 (Single)
//       -1.79769313486232E+308 (Double) --> -Infinity (Single)
//       1.79769313486232E+308 (Double) --> Infinity (Single)
//       -32768 (Int16) --> -32768 (Single)
//       32767 (Int16) --> 32767 (Single)
//       -2147483648 (Int32) --> -2.14748365E+09 (Single)
//       2147483647 (Int32) --> 2.14748365E+09 (Single)
//       -9223372036854775808 (Int64) --> -9.223372E+18 (Single)
//       9223372036854775807 (Int64) --> 9.223372E+18 (Single)
//       -128 (SByte) --> -128 (Single)
//       127 (SByte) --> 127 (Single)
//       0 (UInt16) --> 0 (Single)
//       65535 (UInt16) --> 65535 (Single)
//       0 (UInt32) --> 0 (Single)
//       4294967295 (UInt32) --> 4.2949673E+09 (Single)
//       0 (UInt64) --> 0 (Single)
//       18446744073709551615 (UInt64) --> 1.84467441E+19 (Single)

In addition, the T:System.Double values F:System.Double.NaN, F:System.Double.PositiveInfinity, and F:System.Double.NegativeInfinity covert to F:System.Single.NaN, F:System.Single.PositiveInfinity, and F:System.Single.NegativeInfinity, respectively.

Note that the conversion of the value of some numeric types to a T:System.Single value can involve a loss of precision. As the example illustrates, a loss of precision is possible when converting T:System.Decimal, T:System.Double, T:System.Int32, T:System.Int64, T:System.UInt32, and T:System.UInt64 values to T:System.Single values.

The conversion of a T:System.Single value to a T:System.Double is a widening conversion. The conversion may result in a loss of precision if the T:System.Double type does not have a precise representation for the T:System.Single value.

The conversion of a T:System.Single value to a value of any primitive numeric data type other than a T:System.Double is a narrowing conversion and requires a cast operator (in C#) or a conversion method (in Visual Basic). Values that are outside the range of the target data type, which are defined by the target type's MinValue and MaxValue properties, behave as shown in the following table.

Target type

Result

Any integral type

An T:System.OverflowException exception if the conversion occurs in a checked context.

If the conversion occurs in an unchecked context (the default in C#), the conversion operation succeeds but the value overflows.

Decimal

An T:System.OverflowException exception,

In addition, F:System.Single.NaN, F:System.Single.PositiveInfinity, and F:System.Single.NegativeInfinity throw an T:System.OverflowException for conversions to integers in a checked context, but these values overflow when converted to integers in an unchecked context. For conversions to T:System.Decimal, they always throw an T:System.OverflowException. For conversions to T:System.Double, they convert to F:System.Double.NaN, F:System.Double.PositiveInfinity, and F:System.Double.NegativeInfinity, respectively.

Note that a loss of precision may result from converting a T:System.Single value to another numeric type. In the case of converting non-integral T:System.Double values, as the output from the example shows, the fractional component is lost when the T:System.Single value is either rounded (as in Visual Basic) or truncated (as in C#). For conversions to T:System.Decimal and T:System.Single values, the T:System.Double value may not have a precise representation in the target data type.

The following example converts a number of T:System.Single values to several other numeric types. The conversions occur in a checked context in Visual Basic (the default) and in C# (because of the checked keyword). The output from the example shows the result for conversions in both a checked an unchecked context. You can perform conversions in an unchecked context in Visual Basic by compiling with the /removeintchecks+ compiler switch and in C# by commenting out the checked statement.

using System;

public class Example
{
   public static void Main()
   {
      float[] values = { Single.MinValue, -67890.1234f, -12345.6789f,
                         12345.6789f, 67890.1234f, Single.MaxValue,
                         Single.NaN, Single.PositiveInfinity,
                         Single.NegativeInfinity };
      checked {
         foreach (var value in values) {
            try {
                Int64 lValue = (long) value;
                Console.WriteLine("{0} ({1}) --> {2} (0x{2:X16}) ({3})",
                                  value, value.GetType().Name,
                                  lValue, lValue.GetType().Name);
            }
            catch (OverflowException) {
               Console.WriteLine("Unable to convert {0} to Int64.", value);
            }
            try {
                UInt64 ulValue = (ulong) value;
                Console.WriteLine("{0} ({1}) --> {2} (0x{2:X16}) ({3})",
                                  value, value.GetType().Name,
                                  ulValue, ulValue.GetType().Name);
            }
            catch (OverflowException) {
               Console.WriteLine("Unable to convert {0} to UInt64.", value);
            }
            try {
                Decimal dValue = (decimal) value;
                Console.WriteLine("{0} ({1}) --> {2} ({3})",
                                  value, value.GetType().Name,
                                  dValue, dValue.GetType().Name);
            }
            catch (OverflowException) {
               Console.WriteLine("Unable to convert {0} to Decimal.", value);
            }

            Double dblValue = value;
            Console.WriteLine("{0} ({1}) --> {2} ({3})",
                              value, value.GetType().Name,
                              dblValue, dblValue.GetType().Name);
            Console.WriteLine();
         }
      }
   }
}
// The example displays the following output for conversions performed
// in a checked context:
//       Unable to convert -3.402823E+38 to Int64.
//       Unable to convert -3.402823E+38 to UInt64.
//       Unable to convert -3.402823E+38 to Decimal.
//       -3.402823E+38 (Single) --> -3.40282346638529E+38 (Double)
//
//       -67890.13 (Single) --> -67890 (0xFFFFFFFFFFFEF6CE) (Int64)
//       Unable to convert -67890.13 to UInt64.
//       -67890.13 (Single) --> -67890.12 (Decimal)
//       -67890.13 (Single) --> -67890.125 (Double)
//
//       -12345.68 (Single) --> -12345 (0xFFFFFFFFFFFFCFC7) (Int64)
//       Unable to convert -12345.68 to UInt64.
//       -12345.68 (Single) --> -12345.68 (Decimal)
//       -12345.68 (Single) --> -12345.6787109375 (Double)
//
//       12345.68 (Single) --> 12345 (0x0000000000003039) (Int64)
//       12345.68 (Single) --> 12345 (0x0000000000003039) (UInt64)
//       12345.68 (Single) --> 12345.68 (Decimal)
//       12345.68 (Single) --> 12345.6787109375 (Double)
//
//       67890.13 (Single) --> 67890 (0x0000000000010932) (Int64)
//       67890.13 (Single) --> 67890 (0x0000000000010932) (UInt64)
//       67890.13 (Single) --> 67890.12 (Decimal)
//       67890.13 (Single) --> 67890.125 (Double)
//
//       Unable to convert 3.402823E+38 to Int64.
//       Unable to convert 3.402823E+38 to UInt64.
//       Unable to convert 3.402823E+38 to Decimal.
//       3.402823E+38 (Single) --> 3.40282346638529E+38 (Double)
//
//       Unable to convert NaN to Int64.
//       Unable to convert NaN to UInt64.
//       Unable to convert NaN to Decimal.
//       NaN (Single) --> NaN (Double)
//
//       Unable to convert Infinity to Int64.
//       Unable to convert Infinity to UInt64.
//       Unable to convert Infinity to Decimal.
//       Infinity (Single) --> Infinity (Double)
//
//       Unable to convert -Infinity to Int64.
//       Unable to convert -Infinity to UInt64.
//       Unable to convert -Infinity to Decimal.
//       -Infinity (Single) --> -Infinity (Double)
// The example displays the following output for conversions performed
// in an unchecked context:
//       -3.402823E+38 (Single) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       -3.402823E+38 (Single) --> 9223372036854775808 (0x8000000000000000) (UInt64)
//       Unable to convert -3.402823E+38 to Decimal.
//       -3.402823E+38 (Single) --> -3.40282346638529E+38 (Double)
//
//       -67890.13 (Single) --> -67890 (0xFFFFFFFFFFFEF6CE) (Int64)
//       -67890.13 (Single) --> 18446744073709483726 (0xFFFFFFFFFFFEF6CE) (UInt64)
//       -67890.13 (Single) --> -67890.12 (Decimal)
//       -67890.13 (Single) --> -67890.125 (Double)
//
//       -12345.68 (Single) --> -12345 (0xFFFFFFFFFFFFCFC7) (Int64)
//       -12345.68 (Single) --> 18446744073709539271 (0xFFFFFFFFFFFFCFC7) (UInt64)
//       -12345.68 (Single) --> -12345.68 (Decimal)
//       -12345.68 (Single) --> -12345.6787109375 (Double)
//
//       12345.68 (Single) --> 12345 (0x0000000000003039) (Int64)
//       12345.68 (Single) --> 12345 (0x0000000000003039) (UInt64)
//       12345.68 (Single) --> 12345.68 (Decimal)
//       12345.68 (Single) --> 12345.6787109375 (Double)
//
//       67890.13 (Single) --> 67890 (0x0000000000010932) (Int64)
//       67890.13 (Single) --> 67890 (0x0000000000010932) (UInt64)
//       67890.13 (Single) --> 67890.12 (Decimal)
//       67890.13 (Single) --> 67890.125 (Double)
//
//       3.402823E+38 (Single) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       3.402823E+38 (Single) --> 0 (0x0000000000000000) (UInt64)
//       Unable to convert 3.402823E+38 to Decimal.
//       3.402823E+38 (Single) --> 3.40282346638529E+38 (Double)
//
//       NaN (Single) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       NaN (Single) --> 0 (0x0000000000000000) (UInt64)
//       Unable to convert NaN to Decimal.
//       NaN (Single) --> NaN (Double)
//
//       Infinity (Single) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       Infinity (Single) --> 0 (0x0000000000000000) (UInt64)
//       Unable to convert Infinity to Decimal.
//       Infinity (Single) --> Infinity (Double)
//
//       -Infinity (Single) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       -Infinity (Single) --> 9223372036854775808 (0x8000000000000000) (UInt64)
//       Unable to convert -Infinity to Decimal.
//       -Infinity (Single) --> -Infinity (Double)

For more information on the conversion of numeric types, see Type Conversion in the .NET Framework and Type Conversion Tables in the .NET Framework.

The T:System.Single structure and related types provide methods to perform the following categories of operations:

  • Comparison of values. You can call the Equals method to determine whether two Single values are equal, or the CompareTo method to determine the relationship between two values.

    The T:System.Single structure also supports a complete set of comparison operators. For example, you can test for equality or inequality, or determine whether one value is greater than or equal to another value. If one of the operands is a T:System.Double, the T:System.Single value is converted to a T:System.Double before performing the comparison. If one of the operands is an integral type, it is converted to a T:System.Single before performing the comparison. Although these are widening conversions, they may involve a loss of precision.

    System_CAPS_warningAviso

    Because of differences in precision, two T:System.Single values that you expect to be equal may turn out to be unequal, which affects the result of the comparison. See the Testing for equality section for more information about comparing two T:System.Single values.

    You can also call the M:System.Single.IsNaN(System.Single), M:System.Single.IsInfinity(System.Single), M:System.Single.IsPositiveInfinity(System.Single), and M:System.Single.IsNegativeInfinity(System.Single) methods to test for these special values.

  • Mathematical operations. Common arithmetic operations such as addition, subtraction, multiplication, and division are implemented by language compilers and Common Intermediate Language (CIL) instructions rather than by Single methods. If the other operand in a mathematical operation is a Double, the Single is converted to a Double before performing the operation, and the result of the operation is also a Double value. If the other operand is an integral type, it is converted to a Single before performing the operation, and the result of the operation is also a Single value.

    You can perform other mathematical operations by calling static (Shared in Visual Basic) methods in the T:System.Math class. These include additional methods commonly used for arithmetic (such as M:System.Math.Abs(System.Double), M:System.Math.Sign(System.Double), and M:System.Math.Sqrt(System.Double)), geometry (such as M:System.Math.Cos(System.Double) and M:System.Math.Sin(System.Double)), and calculus (such as M:System.Math.Log(System.Double)). In all cases, the T:System.Single value is converted to a T:System.Double.

    You can also manipulate the individual bits in a T:System.Single value. The M:System.BitConverter.GetBytes(System.Single) method returns its bit pattern in a byte array. By passing that byte array to the M:System.BitConverter.ToInt32(System.Byte[],System.Int32) method, you can also preserve the T:System.Single value's bit pattern in a 32-bit integer.

  • Rounding. Rounding is often used as a technique for reducing the impact of differences between values caused by problems of floating-point representation and precision. You can round a Single value by calling the Math.Round method. However, note that the Single value is converted to a Double before the method is called, and the conversion can involve a loss of precision.

  • Formatting. You can convert a Single value to its string representation by calling the ToString method or by using the composite formatting feature. For information about how format strings control the string representation of floating-point values, see the Cadeias de caracteres de formato numérico padrão and Cadeias de caracteres de formato numérico personalizado topics.

  • Parsing strings. You can convert the string representation of a floating-point value to a Single value by calling the Parse or TryParse method. If the parse operation fails, the Parse method throws an exception, whereas the TryParse method returns false.

  • Type conversion. The Single structure provides an explicit interface implementation for the IConvertible interface, which supports conversion between any two standard .NET Framework data types. Language compilers also support the implicit conversion of values for all other standard numeric types except for the conversion of Double to Single values. Conversion of a value of any standard numeric type other than a Double to a Single is a widening conversion and does not require the use of a casting operator or conversion method.

    However, conversion of 32-bit and 64-bit integer values can involve a loss of precision. The following table lists the differences in precision for 32-bit, 64-bit, and T:System.Double types:

    Type

    Maximum precision (in decimal digits)

    Internal precision (in decimal digits)

    Double

    15

    17

    Int32 and UInt32

    10

    10

    Int64 and UInt64

    19

    19

    Single

    7

    9

    The problem of precision most frequently affects T:System.Single values that are converted to T:System.Double values. In the following example, two values produced by identical division operations are unequal, because one of the values is a single-precision floating point value that is converted to a T:System.Double.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Double value1 = 1/3.0;
          Single sValue2 = 1/3.0f;
          Double value2 = (Double) sValue2;
          Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, 
                                              value1.Equals(value2));
       }
    }
    // The example displays the following output:
    //        0.33333333333333331 = 0.3333333432674408: False
    

Plataforma Universal do Windows
Disponível desde 8
.NET Framework
Disponível desde 1.1
Biblioteca de Classes Portátil
Com suporte no: plataformas portáteis do .NET
Silverlight
Disponível desde 2.0
Windows Phone Silverlight
Disponível desde 7.0
Windows Phone
Disponível desde 8.1

All members of this type are thread safe. Members that appear to modify instance state actually return a new instance initialized with the new value. As with any other type, reading and writing to a shared variable that contains an instance of this type must be protected by a lock to guarantee thread safety.

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